IPI
Bulletin 13

International Potash InstituteBasel/Switzerland

1995

IPI-Bulletin No. 13

Nutrient and Fertilizer
Management in Field
Grown Vegetables
A. Scaife, Ph. D. (Chapters I to 8.1)
Horticulture Research International,
Wellesbourne, Warwick, UK

B. Bar-Yosef, Ph. D. (Chapter 8.2)
Agricultural Research Organization,
Bet Dagan 50250, Israelg@International Potash Institute
P.O. Box 1609
CH-4001 Basel/Switzerland
1995

Contents
Page
Introd uctio n ..............................................................................

7

l.I.
1.2.
1.3.
1.4 .

Economic and environmental factors governing vegetable.. 7grow ing ...................................................................................
7
The importance of a market ......................................................
Temperature and geographical distribution ................................ 8
10
Radiation and rainfall ...............................................................
. . 10
So il ..........................................................................................

2.
2.1.
2.2.
2.3.
2.4.

Principles of crop mineral nutrition ......................................... 11
11
Essential elem ents ........................................................................
Capacity and intensity factors in plant nutrition ....................... 12
13
Consequences for field grown vegetables .................................
Genotypic differences in response to nutrients .......................... 14

3.
3.1.

Diagnosis of nutrient and fertilizer requirements ................ 17
17
Crop response to fertilizer nutrients .........................................
17
Field experimentation ...........................................................
17
Fertilizer response curves .........................................................
19
Simulation models .................................................................
Which elements are deficient or toxic? ................. . . .. .. .. . .. .. . .. . . . 20
20
Indication of nutritional disorders ...........................................
Determination of the nutritional status of plants ...................... 27
27
Plant analysis ........................................................................
28
Tissue and sap tests ...............................................................
29
Diagnostic sprays .................................................................
29
Soil analysis ............................................................................

1.

3.2.
3.2.1.
3.2.2.

3.3.
4.
4.1.
4.1.1.

How much to apply, when, how, and in what form? .... . .. .. . . 29
29
Nitrogen ...................................................................................
29.
Estimating application rates .........................................................
32
ADAS method ........................................................................
33
The German "Nmi n " system ....................................................
33
The "KNS" system .................................................................
33
the
KNS
method............................
Possible modifications to
Simulation models and Expert Systems ................................ 34
34
Sap testing ............................................................................
34
The "Diingefenster" . ..............................................................
Conclusions regarding N prediction methods ....................... 353

4.1.2.

4.4.
4.4.1.
4.4.2.
4.4.3.
4.4.4.
4.5.
4.6.

Choice of N fertilizer ...................................................................
35
Materialsavailable ..............................................................
35
Nitrate versus ammonium .....................................................
36
Slow release N-fertilizers ......................................................
37
Nitrification inhibitors ..........................................................
37
Aqueous ammonia, anhydrous ammonia and"ammonium-depots". ...........................................................
37
M ethods of applying nitrogen .................................................
38
Single broadcast base dressing .............................................
38
Split dressings .......................................................................
38
Starter fertilizers, placement and banding ...........................
38
Foliar feeding .......................................................................
40
Phosphorus ...............................................................................
40
Application philosophy for P and K ........................................
40
Phosphorus fertilizers ..............................................................
41
M ethods of applying P ............................................................
42
Potassium ...............................................
42
Amounts of K to apply ............................................................
42
Potassium-containing fertilizers ...............................................
44
The best potash fertilizer and methods of application ............. 45
Chloride or sulphate ofpotash? ..........................................
45
Methods of application ..........................................................
45
Secondary nutrients ................................................................
46
Calcium-related physiological disorders ..................................
46
M agnesium deficiency ............................................................
46
Sulphur ....................................................................................
47
Sodium ......................................................................................
47
M icronutrients (trace elements) ...............................................
47
Soil pH adjustment ..................................................................
48

5.

The organic approach ............................................................

50

6.

Vegetable nutrition and crop quality ....................................
Nitrogen ...............................................................................
Other elements ......................................................................

51
51
53

7.

Interaction with pests, diseases, and environmental stress ..... 53

8.
8.1.

Crop specific fertilizer management and recommendations .. 54
Vegetables grown under temperate conditions ........................
54

8.2.
8.2.1.

Fertigated vegetables in arid and semi-arid zones ....................
Principles of com bined irrigation and fertilization ..................

4.1.3.

4.2.
4.2.1.
4.2.2.
4.2.3.
4.3.
4.3.1.
4.3.2.
4.3.3.

4

66
66

8.2.1.1. Introduction ..............................................................................
8.2.1.2. Quantity considerations ..........................................................
8.2.1.3. Intensity considerations ..........................................................
8.2.1.4. Importance of flux-concentration relationships .......................
8.2.1.5. Coupling quantity and intensity factors ..................................
8.2.1.6. Root growth in soils .................................................................
8.2.2. Managing vegetables fertigation .............................................
8.2.2.1. N, P, K target consumption rates [Q(t)] and supply ..........
8.2.2.2. Nutrient concentrations in irrigation and soil solutions ...........
8.2.2.3. Selecting fertilizers for fertigation ...........................................
Fertigationundersaline conditions ........................................
Fertigationsolution pH ..........................................................
Nutrient mobility in soils ..........................................................
Ready-mix fertilizers .................................................................
8.2.3. M onitoring the plant-soil system .............................................
8.2.4. Concluding remarks .................................................................

66
66
67
68
70
70
74
74
82
84
85
85
86
87
87
88

References (Chapters I to 8.1) ...............................................

89

References (Chapter 8.2) ...........................................................

100

5Introduction
Vegetables are mostly high value crops and small yield losses due toimperfect mineral nutrition, which would be difficult to measure in a field
experiment, can result in a substantial loss of profit. If this is to be avoided,
the grower must use every means at his disposal to optimise nutritional
practices, and this is most likely to be achieved by a thorough understandingof the principles involved.
Very often, vegetable growers are forced by the market to achieve
exaggerated crop standards, like very specific size and appearance, total
freedom from blemishes or complete absence of pesticide residues andextremely low concentrations of nitrate, which is in fact a normal constituentof plants.
At present, questions of flavour, texture and dietary value of vegetables
receive very little attention from either scientists or supermarkets but there
are signs that this attitude is changing.
Finally, it has to be recognised that a successful nutrient management invegetable growing is characterized by minimal water and air pollution.
Information about the influence of mineral nutrition and fertilizer
management on these factors will be given in the following chapters.

1. Economic and environmental factors governing vegetable
growing1.1. The importance of a market
In the past, the predominant factor which governed commercial
vegetable growing was the proximity of a suitable market. With ingenuity
and perseverence, it is possible to grow vegetables almost anywhere,
although a warm sheltered site and a light, well-drained soil with a goodorganic matter content are desirable. The availability of a substantial labour
force, primarily for the harvesting and preparation of the crop for sale, isalso essential, although mechanisation of these processes is steadily
increasing. At the end the the second world war, UK vegetable production
was concentrated on the fringes of major towns and in certain climaticallyfavoured areas such as the Vale of Evesham. This was no doubt the situationin most industrialised temperate countries, and it is still found in many partsof the world.

7

With the rapid advance of mechanisation and the use of agrochemicals,
however, and the ability to deliver the produce by road, rail and plane overconsiderable distances, production moved more to areas where the mostfavourable environmental conditions for vegetable growing are found.
Meanwhile, in most industrialised countries, sale of the produce
gradually switched from the greengrocer or market stall to the supermarket,
and consumers, who before the fifties were accustomed to eating quite
different vegetables in each season, began to expect to be offered a complete
range of produce throughout the year. At first, this demand was satisfied by
the processing industry, which by the establishment of canning and freezing
plants, also influenced the siting of production of certain crops. However,with the growth of the "affluent society", the consumer demanded fresh
produce, and supermarkets responded by importing produce, often by plane,from all over the world. These and other recent trends in the vegetableindustry have been described for the UK by Wright (1994).
1.2. Temperature and geographical distribution
This world trade is a reflection of the fact that the most important
climatic factor in vegetable growing, particularly for winter supplies intemperate regions, is temperature. Vegetable plants tend to be more widely
spaced apart than those of arable crops and to have smaller seeds.
Particularly when they are grown as direct-drilled crops, therefore, they havea long exponential growth phase when they grow at about 15-25% per day,this rate being determined by temperature rather than radiation receipt.
Development is also highly temperature-dependent. The minimum
temperature for growth is between 0 and about 60 C (much higher for "warmseason" species such as tomato), and the optimum is generally in the mid20s (Table 1). An increase of 2-3°C (such as is obtained by the use of plastic
covers) can have a very marked effect on maturity date, and because of thedemand for year-round production of each type of produce, these effects
dominate the profitability of production and influence the movement ofareas of production around the world. For example, although California
produces most of the summer vegetables for the USA, Florida producesthem for the winter (Maynard and Locascio, 1982). In Europe, The Netherlands provides a very large share of the field-grown summer vegetables andthe protected crops (tomatoes, cucumbers, peppers), whilst Spain and Italy
provide much of the winter produce (Hinton, 1991). In Sweden and Finland,horticultural production is concentrated in the southernmost part of eachcountry (Vesanto and Lehtimaki, 1993), whereas in Norway it is confined by
the topography and proximity of the main markets (Balvoll, 1989).
8

Table 1. Temperature requirements (0C) for vegetable crops (Maynard andLorenz, 1988).
Optimum

Minimum

Maximum

13-24

7

29

16-18

4

24

16-18

7

24

16-21
16-24
18-24
18-24
21-24
21-29

10
10
10
16
18
18

27
35
32
32
27
35

Vegetable
Chicory, chive, garlic, leek, onion,
shallot
Beet, broad bean, broccoli, Brussels
sprout, cabbage, kohlrabi, parsnip,
radish, swede, spinach, turnip
Carrot, cauliflower, celeriac, celery,
Chinese cabbage, endive, Florence
fennel, lettuce, parsley, pea
French bean
Sweet corn, New Zealand spinach
Pumpkin, squash
Cucumber, muskmelon
Sweet pepper, tomato
Eggplant, chilli pepper, okra, watermelon

After the exponential growth phase, there is usually a linear phase when
1 -1
the growth rate is about 250 kg dry matter ha- d , and for many species
which are harvested whilst still growing, this may be the final phase(Greenwood et al., 1977), although the growth of species which remain in
the ground into the winter may slow down because of low temperature andlack of light. Others, notably onions, mature and stop growing as a result of
ontogeny, and the same would apply to other determinate crops such asbeans if they were allowed to grow beyond their normal harvesting time asgreen vegetables.
Whilst low temperatures often set the northern geographical limits ofproduction (in the northern hemisphere), or an altitude limit in mountainous
regions, the high temperatures (especially at night) of tropical regions meanthat the "cool-season" vegetable crops traditionally grown in Europe may
only be grown in the "winter", or at high altitude, in the tropics.
Another temperature-related aspect is freedom from severe frosts. For
example, there are coastal zones, such as south-west England, south-west
Wales, Brittany and Long Island (USA), which enjoy mild winters becauseof the Gulf Stream effect and are therefore used for the production of wintercrops like winter cauliflower, which cannot tolerate severe frost.
91.3. Radiation and rainfall
Climatic factors other than temperature are less important in restricting
production. If rainfall is at all marginal, irrigation is essential for many
species. The total water requirement is determined largely by theevaporative demand of the atmosphere, and there are various systems
available for calculating it, using the principles established by Penman(1948). Water quality, i.e. salinity or the toxic effects of particular elements
such as boron, are not normally a problem in temperate zones, but in thesemi-arid and arid subtropics and tropics, poor water quality might be aserious limitation. To manage these difficulties, the reader should refer toLorenz and Maynard (1988).
Solar radiation is of course the prime source of energy for crop growth,and its efficient interception (for example by the use of transplanting rather
than direct drilling into the field) is the key to high productivity per unit landarea. However, radiation only becomes a factor limiting growth once thecrop is fairly advanced, and leaves begin to shade one another (Bierhuizen etal., 1973).

1.4. Soil
In general, well-drained soils such as deep silts, fine sandy loams,
organic soils or strongly weathered permeable soils, are usually preferred forvegetable production because of their suitability for working at most timesof the year. Clay soils are rarely used except for some brassica crops such as
Brussels sprouts, and light sandy soils are favoured for root crops,
particularly carrots and parsnips, which are easily harvested from such soils
with minimal washing problems. Peat (muck) soils have been much used forcelery, onions, carrots, and salad crops, but their extent is decreasing
because vegetable growing is linked with intensive soil aeration and tillage,
which accelerates unfavourable peat oxidation.
Inherent low nutrient supplying capacity of the soil and an acid soil
reaction can usually be corrected. A clear example of how soils with nutrient
deficiencies can be made productive in an area with favourable wintertemperatures is the state of Florida, where 161 000 ha of poor soils (inplaces mere rock) supply the USA with most of its winter vegetable needs(Maynard and Locascio, 1982). Lime-induced iron chlorosis is much rarer invegetables than in fruit crops, but other micronutrient deficiencies associatedwith high pH can be troublesome, so that alkaline soils are best avoided,
except for brassica crops.

l0

2. Principles of crop mineral nutrition
2.1. Essential elements
Plants require 12 or 13 mineral elements (Table 2) in order to grow (seeMengel and Kirkby, 1987; and Marschner, 1986 for a full description of thefunctions of these elements and their behaviour in soil, etc.).
If the supply of any one of these fails to keep pace with the demand, its
average concentration in the plant will fall due to dilution by growth, which
may slow down. In the case of certain immobile elements such as calcium
and boron, new growth will exhibit symptoms of the deficiency, such as
necrosis. To avoid these effects, the grower must either supplement thenatural supply of nutrients from the soil with inorganic fertilizers, organic
manures, or foliar feeds, or else modify it by adjusting the pH. The element
most often deficient (although representing 80% of the atmosphere) is
nitrogen (N), and despite the objections of the environmentalists, it is
impossible to imagine world agriculture without "bag" nitrogen. Many soils
also require regular additions of phosphorus (P) and potassium (K), but it isperhaps surprising that most soils continue to supply the other 9-10 elements
without quickly becoming quickly exhausted.
Table 2. Essential elements for plant growth and their approximate criticalconcentrations (see Fig. 4) in "Youngest fully-expanded leaves" (YFEL) in
mid-growth. Concentrations marked* have no diagnostic value but are
simply fairly typical. Fuller details, applicable to different species, are given
by Reuter and Robinson (1986).
Element
Nitrogen (N)Phosphorus (P)Potassium (K)Calcium (Ca)
Magnesium (Mg)
Sulphur (S)Iron (Fe)Manganese (Mn)
Zinc (Zn)
Copper (Cu)Boron (B)
Molybdenum (Mo)
Chloride (CI)

Critical concentration (in dry matter)
3.5 %0.35 %
2.0%
1.0 %*
0.2%
0.2 % (0.35 for Crucifers)
100 pig g-'*
20 pg g-I
20 pig g-1
5 pig g-1
20 pig g-1
0.1 pag g-1
100 pg g-1
I1

2.2. Capacity and intensity factors in plant nutrition
In order to understand crop demand for nutrients, it is helpful to consider
a plant growing in a large tank of vigorously stirred nutrient solution. Some
classical experiments (Olsen, 1950; Clement et al., 1978; Williams, 1961)
have shown that in such a situation, only very low concentrations (such as
0.1 mg N [I-) are required to satisfy the demand of the plant. This is because
the root surfaces have a powerful affinity for the nutrient ions, which arecarried to them by the "mass flow" created by the stirring. If the stirring
stops, a depleted zone forms around the roots, which then depend on the ion
diffusing from the bulk solution to the root surface. This means that a higher
concentration is then needed in the bulk solution in order the "drive" the ions
down a concentration gradient, and still provide the necessary critical concentration at the root surface (Milthorpe and Moorby, 1974). In soil-growncrops, such "downhill" gradients exist for most nutrient ions at most times,
except those, such as calcium and magnesium, which exist at such highconcentrations in the soil solution that they are swept to the root by the mass
flow of the transpiration stream faster than they are needed by the plant.
These ions may actually accumulate at the root surface (Barber, 1962).
For "unbuffered" nutrients, such as nitrate, this tank analogy represents
the situation in soil quite well: most of the nutrient in the rooting zone isaccessible to the plant, so the total amount of nutrients measured in the soil
is a good indication of availability.
However, most nutrients, notably cations such as ammonium, potassium,
calcium and magnesium, are not only present in the soil solution, but arealso "adsorbed" by electrical attraction, to the clay and humus particles inthe soil. Some, such as phosphate and borate, may also be present as
sparingly soluble salts which may enter the soil solution (and thus become
available for uptake) only very slowly, and only when the pH favours theirsolution. These adsorbed or insoluble forms act as a "buffer" or reserve,
which tends to replenish the soil solution when it is depleted of an ion byroot adsorption. Those fractions of a nutrient which are dissolved in the soil
solution or very readily exchangeable with it are referred to as the "labilepool" of that nutrient. The soil solution concentration, which is what theplant senses, is called the "intensity factor" whereas the reserve available forreplenishing the soil solution fairly quickly is called the "quantity" or"capacity" factor. Analytical methods for these buffered nutrients usually
represent the quantity rather than the intensity, but in clayey soils, this may
give an overestimate of the concentration in the soil solution (see Fig. I).

12

A
0

sand

clay

pat

Quantity factor (e.g. exchangeable K/g soil) >Fig. 1. Formalised quantity-intensity relationships for different soil types. In
the sandy soil, the soil solution concentration is high but the quantity
available to buffer it is low: clay and peat soils hold a lot of P and cations
but the soil solution concentration tends to be low.
The upper concentration limit in the rhizosphere for many nutrient ionsis determined by the "salt effect", i.e. the total osmotic strength of thesolution, which should not exceed 1-2 bars (0.1-0.2 MPa) (Kramer, 1949).
Some, such as the borate ion, may have specific toxic effects far in excess ofthat due to osmotic pressure (Lorenz and Maynard, 1988). The point to bemade here is that the secret of optimising crop nutrition is to maintain theroot surface concentration of all nutrient ions above their critical level whilst
avoiding the build-up of damaging salt concentrations. The latter isaggravated by soil drying.

2.3. Consequences for field grown vegetables
From the above, it can be seen that for cations, which are adsorbed onto
clay, and indeed for phosphate, which is not only adsorbed but alsoprecipitated, it is necessary, right from the earliest stage of plantestablishment, to raise the equilibrium concentration around the roots to thepoint where the soil solution concentration is above the critical level which
they need. For phosphorus, this appears to be about 1.4 VaM (0.04 ppm P) for
P-efficient species, and 7 piM (0.2 ppm P) for inefficient ones (Fbhse el at.,1988) (see 2.4.).
13

This may require a substantial, albeit localised, application of thenutrient, the amount of which will depend on the adsorbing properties of thesoil. Thereafter, depletion of these ions from the rhizosphere may haverather little effect on the soil solution concentration because of desorption
from the exchange medium.
Because of these effects of nutrient adsorption and desorption, it iscommon in fertilizer experiments to see a response to buffered nutrients very
early in crop life, even to high rates of application. For nitrate-N, which is
not buffered by the soil, the benefit of the high rates, which at the seedlingstage sometimes may retard the growth, only becomes apparent during theso-called "grand period of growth" when the crop is depleting the soil
mineral N to a low concentration (Scaife et al., 1986). In order to understandthe timing of these effects (and hence make enlightened decisions about
fertilizer placement, etc.), it is useful when doing fertilizer experiments tomake weekly destructive or non-destructive estimates of plant size, and toplot their logarithms against time. In the example shown in Fig. 2, this formof plot suggested that P response was complete soon after emergence, after
which plants on all P treatments grew with the same relative growth rate,
although their absolute growth rate was governed by the size differences
established when they were young.
It should be clear from the above that while crops are growing they exert
a demand for nutrients which means that a rather high soil solution
concentration is needed to drive the nutrients across the diffusion barrier tothe root surface. What distinguishes many vegetable crops from most arable
crops is that the former are still growing, often very fast, at the time of
harvest, whereas most arable crops have stopped. Vegetable crops therefore
need to be given enough fertilizer, notably N, to maintain growth at harvest
time, and this is why they leave much higher residues nutrient in the soil
than arable crops.

2.4. Genotypic differences in response to nutrients
Relatively little research work has been done to explain why one species
or variety differs from another in its response to nutrients under field
conditions. The subject has been reviewed by Barker (1989). Plant
physiologists working with stirred nutrient solutions have attempted tocharacterise the response of different genotypes in terms of kinetic
parameters. Clarkson and Hanson (1980) reviewed this approach andconcluded that plants have a very high affinity for nutrients and that theamount transported is regulated largely by demand.
14

200

(a)
M0 p
A 140 kg Pz0 5 /ha

-C

150

7

880 kg P2O5/ha

-

'A

C

'I/

C

100 "

7/

5
0~

0.05

0.5

40

30

20

10
500

50

(bI

4

-

0

Days from emergenceFig. 2. Lettuce growth with 3 levels of broadcast basal P fertilizer, plotted(a) on a linear scale, and (b) on a logarithmic scale. The latter makes it clearthat response occurred within 19 d of emergence (Scaife, unpublished data).
In the case of nitrogen, because of the unbuffered nature of nitrate in thesoil, differences can be explained to some extent in terms of the total amountof N in the crop when it reaches physiological maturity. However, certain
species seem not to fit this view: for example, the root crops, carrots,
parsnips, swedes and turnips remove 150-350 kg N ha - 1, but are very
unresponsive to applied N (NVRS, 1980; Sorensen, 1993).
15

One factor which might explain some such cases is the dynamics of thesystem: a crop requiring 100 kg N ha-1 over a six-month growth period
might be fully satisfied by natural soil mineralization (see 4.1.1.), whereas
one needing the same amount over a shorter growth period might require
some extra N as fertilizer, because its needs outpace the mineralization rate.
For buffered elements, such as P and K, the dissimilarity between uptake
and responsiveness is even more striking. For example, lettuce and spinach
are highly responsive to P, but only take up about 16 and 30 kg P20 5 ha-1
respectively, whereas summer cabbage, which is unresponsive, takes up 50
kg ha-t (Greenwood et al., 1980b). F6hse et al. (1991) have shown thatspecies differences in P efficiency are attributable to uptake factors such as
root length or uptake rate per unit root length, rather than the amount ofgrowth made per mg P taken up. Root hairs were the characteristic feature ofefficient species. Claasen (1992) referred to work showing how acidificationof the rhizosphere by the roots can influence P uptake. Variable infection by
vesicular-arbuscular mycorrhizae (VAM), which infect most species apartfrom Cruciferae and Chenopodiaceae (Marschner, 1986), could also be
relevant (Mayer et al., 1989; Krikun et al., 1990).
Micronutrients are normally present in soils in large quantities (relative
to crop demand) but their availability to plants is limited by their solubility.
For iron uptake, certain genotypes are strikingly "iron-efficient" and thisefficiency is induced by iron stress and may be controlled by a single gene
(Brown, 1978). Excretion of H' and HCO 3 ions, which is enhanced byammonium as opposed to nitrate uptake, is responsible for most of these"solubilizing" effects of roots (Marschner, 1986).
Breeding for efficiency of nutrient uptake is clearly worthwhile for thoseelements which are present in large quantities in the soil, and can be madeavailable by root exudates, etc; it is less likely to work for unbufferedelements like nitrogen and sulphur.
NOTE
In this book, we have frequently expressed amounts of phosphorus andpotassium as their oxides, P 20 5 and K2 0, as is customary on fertilizer bags.
To convert amounts or concentrations in these units to P and K, multiply by
0.44 and 0.83 respectively.
Nitrate concentrations in plants and soils are sometimes expressed as
nitrate (NO 3) (e.g. by the European Union authorities) and sometimes asnitrate-N (NO 3N). To convert from the former to the latter, multiply by 0.23.
The word "nitrate" should mean NO 3.
Whenever these units are discussed, it is important to make clear which
form of expression is being used.
16

3. Diagnosis of nutrient and fertilizer requirements
3.1. Crop response to fertilizer nutrients
Field experimentation
Not enough is known about crop demand for nutrients, and their releasefrom soil, to enable us to calculate optimal fertilizer requirements from firstprinciples. Since fertilizers were invented in the mid-19th century, therefore,
the empirical approach of experimenting in the field or with pots has beenmuch used. The two questions which such experiments seek to answer are"which elements are deficient?" or "how much of element X should I
apply?"
The first is best answered by a "factorial" experiment of 2n design, i.e.
including several nutrients, each at two levels (absent and present). For thesecond, at least five levels of application are needed to define the "response
curve". In both cases, great attention to correct statistical technique is needed
unless large responses can be expected.

Fertilizer response curves
Assuming that we have carried out a response-curve type of experimentwith five or more levels of a nutrient X, recorded the yields obtained, andminimised the error (for example, by covariance on plant density), the next
problem is to find the optimal level of X (giving the highest yield Y) or the
economic optimum (giving the highest financial profit from the use of X).
One method, not favoured by statisticians, is to simply plot Y against X,
indicating the magnitude of the error calculated from the analysis ofvariance, and to use a flexible plastic rule to draw a smooth curve whichconnects the points as closely as seems to be required by the size of theerror. It may be necessary to make certain rules about the shape of the curve(e.g. it should never level out and then turn upwards), and to ask an unbiased
colleague to draw the curve to ensure impartiality. The horizontal tangent to
the peak of the curve gives the position of the optimum on the X-axis. If the
Y-axis is expressed in monetary values, and the cost of the fertilizer isshown as a straight line (Fig. 3), then the economic optimum may be foundwhere a line parallel to this line makes a tangent to the crop response curve.
With vegetable crops, it is often the case that the economic optimum isvirtually the same as the optimum for yield, because of the high value of thecrop compared with the cost of fertilizer.
17

20 '

"Ceiling yield, A

15000
D

S15-

0
10000
C

o
-6

N

10Cotrol yield

4,U

5000
5- -0

Cost of fertilizer

0
-50

0

Soil N (x,)

50

100

150

200

250

0

300

0

a

U

N applied, kg/ha (x,)

Fig. 3. Mitscherlich response curve and its use to find the optimum fertilizer
dressing. The equation of the curve is Y = A (I - eC(xs xf)), where:
A is the ceiling yield when x = o, (20 t/ha),
xf is the amount of nutrient applied,
xs is the amount of this nutrient supplied by the soil, expressed in thesame units as xf, (40 kg/ha),c is the "curvature term" calculated from Ilni- (= 0.0125)
xi it
The economic optimum occurs where the slope of the response curve
equals that of the cost curve, i.e. at about 300 kg/ha. Figures apply tocauliflower grown on a light soil.
The advantage of using one of the numerous mathematical equations
available to define such curves (such as that of Mitscherlich, 1909) is thatthey provide parameter values which describe the shape of the curve (seecaption to Fig. 3). If a large number of experimental results from scatteredsites are available, this enables one to relate these parameter values toappropriate soil or environmental measures which may then provide a systemfor predicting responses over a large geographical area (Scaife, 1968).
A complication is that fertilizer response curves often show a "downturn"at high application levels. Mitscherlich observed this, and modified his
equation accordingly (Mitscherlich, 1928). The downturn may manifest
itself in a great variety of ways. Salt damage to emerging seedlings,
including actual loss of plant stand, is common when vegetable crops are
drilled into a seedbed treated with nitrate, especially in dry weather. As little
as 50 kg N ha-1 can depress lettuce yields because of this (Page and Cleaver,1983). This is a major reason for using split nitrogen applications.
18Mitscherlich was adamant that c (the parameter describing the sharpnessof curvature of his response curve) should not vary for a particular nutrient,
but it is not difficult to think of reasons why it should. In the case ofphosphorus, for example, we know that highly P-fixing soils require hugequantities of P (unless it is suitably placed) to reach maximum yield,
whereas this is less true on non-fixing soils. For nitrogen, it is clear that if
heavy rain washes a large proportion of the nitrate out of the rooting zone, amuch higher initial dose will be needed to produce maximum yield than if
no such leaching occurs.

Simulation models
This last example can help to explain why various workers (Scaife, 1974;
Hansen et al., 1993; Greenwood et al., 1974) came to the conclusion that the"curve-fitting" approach to interpreting fertilizer experiments wasinadequate. If the leaching event occurs shortly after the N is applied, it will
obviously have a big effect on the final response, but if it occurs after thecrop has absorbed most of the N, there will be little or no effect. The timingof the rainfall in relation to the stage of development of the crop is therefore
important, and this suggests that a dynamic approach is needed. Indeed,
consideration of the numerous nitrogen transformations taking place in thesoil leads one to the same conclusion.
Another reason for needing a dynamic approach in the case of vegetable
crops is that unlike most arable crops, they are often still growing rapidly at
the time of harvest. For certain crops such as leeks and carrots, there is no
particular moment of maturity, and the grower may wish to know whether
fertilizer requirement for an early harvest is the same as for a late one.
Others, such as lettuce and cauliflower, are harvested shortly before they"bolt", and the question arises as to whether the yield shortfall due toinadequate nutrition can be made good by deferring harvest for a few days
(Bums, 1990). If maturity date is unaffected by crop nutrient status, itcannot. As a general rule, all field experiments with this type of vegetable
crop (not merely nutritional ones) should be harvested in such a way as toprovide not only the yield but also the "50% maturity date". The moreobjective way to find the latter is by means a of series of destructive
harvests, bracketing the maturation period for all the treatments, but thisgreatly increases the size of the experiment. Most research workers adopt a"cut-over" policy similar to commercial practice, whereby the person cutting
the heads makes a subjective judgement, either by eye or by "feel" as towhether a plant is ready to cut.
19

The dynamic approach means that a complex mathematical model isbuilt up as a series of relationships connecting what the modeller considers
to be relevant parts of the system. Typically, the growth of the crop
(unlimited by water and nutrients) is a function of initial plant weight,
density, temperature and radiation. Growth of the root system down the soil
profile is simulated, although few, if any, models allow for the known
adaptation of root growth to soil water and nutrient "pockets" which has
been known about since 1892 (Barley, 1970). Nutrient demand is the
product of the growth rate (unlimited by the nutrient) and an optimal
nutrient percentage which varies with growth stage (Greenwood et al.,1978). Estimating the supply is more difficult, and tends to be based on thewhole rooted zone at any given moment rather than the rhizosphere. For
nitrogen (which has been the main interest of these models) the varioustransformations, including leaching through successive layers of soil (Bums,
1974) are modelled. The computer proceeds in daily (or smaller) time-steps
to update the values of each variable in the system.
Although these simulation models offer a possible solution to thecomplexities of crop nutrition, they also confront the modeller with a host of
new problems, not least of which is that of predicting the growth curves ofplants over as much as five orders of magnitude. For the user, they offer the
possibility of simulating various scenarios, and perhaps of making use of theexperience to plan field experiments. It is unwise to use them as a "blackbox": the user should find out what assumptions are built into them.

3.2. Which elements are deficiint or toxic?
3.2. 1. Indication of nutritional disorders
Growers and their advisers should familiarize themselves with thesymptoms of nutrient deficiencies and toxicities; which are illustrated inseveral publications (Scaife and Turner, 1983; Sprague, 1964; Bergmann
and Neubert, 1983; Wallace, 1961). Some symptoms may be confused withthose of virus attack or pesticide damage, and it is important, whenattempting to diagnose such problems, to visit the field concerned, to spend
time talking over the various possibilities, and to confirm the diagnosis byleaf analysis, if this is appropriate. Susceptibility of species to each disorder
is indicated in Table 3, together with a brief description of the symptoms.
Plates 1-6 show some common deficiency symptoms.

20

Table 3. Nutritional disorders in vegetables and predisposing factors.
Nutrient/mineralelements
Deficiency
Nitrogen

Deficiency and toxicity symptoms - Predisposing factors

Poor growth; pale leaves, especially old ones; pink and purple tinges on leaves and petioles ofbrassicas; red beet leaves deep purple and spotted; petiole or midrib "sap" nitrate concentration
The most ubiquitous nutrient
measured with "Merckoquant" test strips will be below 250 mg NO3 1-1.
deficiency throughout the world on all but highly organic soils.

Phosphorus

Sometimes older leaves show purple tinges (on undersides for brassicas) especially in cold weather;but growth, especially of seedlings, may be severely restricted with virtually no symptom; leaf and soil
analysis useful.

Potassium

Marginal scorch and upward curling of older leaves; shrivelling of old carrot, onion, and leek leaves;leaf and soil analysis useful. As for P deficiency, rarely seen because of liberal PK applications.

Calcium

Necrosis of growing point or young leaf edges (lettuce tip-bum; brassicas, internal browning ofBrussels sprout buttons; blackheart of celery); leaf cupping and puckering of edges. In practice, thedisorders are usually due to localised failure of calcium transport; soil analysis not useful; plant
analysis only if soluble Ca measured in susceptible tissues.

Magnesium

Interveinal chlorosis (yellowing) of older leaves; sometimes leaf edges stay green (e.g. pea); red tints
may move in from leaf margins (carrot, swede); or chlorosis moving in from leaf margin (celery); leaf
blistering in red beet; in lettuce, chlorosis can be confused with beet western yellows virus attack: leaf
and soil analysis useful.
I~/Table 3. (continued).
Nutrient/mineralelements
Deficiency
Sulphur

Deficiency and toxicity symptoms - Predisposing factors

May resemble nitrogen deficiency but sap nitrate concentration will be normal or high; pale colours on
young rather than old leaves; in brassicas bronzing and cupping of new leaves; leaf analysis useful;soil less so. Becoming commoner as atmospheric sulphur dioxide falls.

Iron

Very rare in vegetables; whitening of young leaves, with veins remaining green initially; can occur inhydroponic systems. In soil, it may be induced by heavy metal toxicity (e.g. Cu, Ni, Zn from sewage
sludge - see Archer, 1988), or if the soil is calcareous and waterlogged. Soil analysis not useful (except
to indicate free CaCO 3 or excess heavy metals); leaf analysis for total Fe not useful; some authors (Raoet al., 1987) advocate measuring ferrous iron in fresh tissue.

Manganese

Similar to magnesium deficiency but usually a finer and fainter interveinal chlorosis, often over thewhole plant or especially on young leaves. Longitudinal chlorotic striping of older onion leaves.
"Marsh spot" (hollows or discolouration inside seeds) of peas and beans. Common in UK, especiallyon peaty or organic soils above pH 6.0 or on sands above pH 6.5 (Archer, 1988). Leaf analysis very
useful, but not soil.

Zinc

An important deficiency in many countries notably USA, Australia, India and in the Middle East, butmuch less common in Europe; causes longitudinal chlorotic striping and leaf twisting in onions, andinterveinal striping leading to pure white young leaves in sweet corn ("white bud"); pitcher-shaped
leaves in cabbage; aggravated by high pH, heavy P fertilization, and cool, overcast weather (Thome,1957). Soil (especially DTPA extraction) and leaf analysis useful (Lindsay, 1972).

Table 3. (continued).
Nutrient/mineralelements
Deficiency
CopperF-)

Deficiency and toxicity symptoms - Predisposing factors

Common on newly reclaimed peat soils, irrespective of pH, throughout the world; young carrot leaves
dark green, do not unfold; older leaves limp; lettuce leaves elongated, chlorotic at edges, limp; onion
bulbs pale with thin yellow scales (Purvis and Carolus, 1964). Soil analysis (DTPA or EDTA extract)
useful; leaf analysis not so; ADAS (UK advisory service) recommends test spraying of small area ofcrop, which shows a response in 7-10 d (Archer, 1988).

Boron

Suspected of involvement with numerous disorders but proof is often lacking: causes death of growing
point, brittleness and thickening of tissues, corky lesions on midribs, petioles, stems; transverse cracks("cat-scratch") on petioles; brown heart of swede roots; cankerous skin and hard black lesions inside
beetroots; brown or undeveloped curd on cauliflower; hollows in tissues (but see Scaife and Wurr,
1990, re. hollow stem of cauliflower). Occurs on light soils generally above pH 6.5 or recently limed,particularly in dry summers following a wet spring (Fatrer, Caldwell and Archer, 1976). Soil (hot watersoluble B in UK) and leaf analysis useful, though critical concentrations rather doubtful.

Molybdenum

Affects cauliflower, causing "whiptail" - leaf lamina is reduced leaving mainly midribs; lettuce
occasionally affected - leaves turn pale, papery and ovate in shape, necrotic at edges; plants fail to heartand may die (Plant, 1956). Mo is the only micronutrient deficiency to occur on acid soils, andcorrection of pH prevents it for all crops except occasionally cauliflower. Leaf analysis preferred to soil
"1.
analysis, but great analytical precision needed because critical concentration is only 0.1 mg Mo kg

Chloride

Essential element but for practical purpose it can be ignored.

Table 3. (continued).
Nutrient/mineralelements
Toxicity
Manganese

Aluminium

Boron

Ammonia

Chloride
Copper, Nickel,
Zinc

Deficiency and toxicity symptoms - Predisposing factors

May occur as part of "soil acidity complex" (Wallace, 1961; Hewitt, 1983) if pH falls below 5.0.
Brassica crops show inward rolling of leaf edges, interveinal chlorosis, and necrotic spotting. Lettuce
older leaf edges become golden yellow. Mn concentrations above 500 mg kg-I in the affected leaf
margins would indicate the problem (MacNicol and Beckett, 1985). Bussler (1958) described themicroscopic effects.
Whereas brassicas suffer Mn toxicity on acid soils, certain crops, notably sugar beet and celery are
resistant to it, but instead suffer from aluminium toxicity, to which brassicas are tolerant (Hewitt,1983). Symptoms are mainly on the roots - thickening, clubbing, and blackening, although celeryshows petiole collapse and necrosis of the growing point.
This occurs mainly as a result of over-dosing when attempting to correct B deficiency (which is very
easily done) and when irrigation water contains more than about 0.75 mg B I- (Lorenz and Maynard,
1988). Lettuce is rather susceptible: older leaves show pale margins.
Wilting, interveinal and marginal necrosis (scorch) of leaves; brown roots. Tissue NH 4+ concentration
is diagnostic but critical value is genotype-dependent (Barker, 1989). May occur in compost-grownplants following steam sterilisation, or storage of the compost (Bunt, 1976).
May occur in saline conditions. Causes marginal leaf scorch similar to K deficiency.
See iron deficiency.

Nttj'nCfl d<ItLdrc

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26

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.2.2. Determination of the nutritional status of plants
Plant analysis
The introduction of leaf analysis as a diagnostic technique is attributed to
Lagatu and Maume (1924). Leaves (usually defined as those which are"youngest fully-expanded") are sampled from at least 25 randomly-scatteredplants in the crop, preferably at a definable growth stage. For the immobile
elements calcium, copper and sulphur, young leaves should be sampled. For
details of sample preparation, see Bould (1983). After analysis,
interpretation depends on the "critical concentration".
The classical "text-book" explanation of critical plant nutrient
concentrations is as shown in Fig. 4. A pot or field experiment is done withincreasing levels of the nutrient of interest, and the final yields are plottedagainst the concentrations of that nutrient measured in particular, carefully
defined tissues analysed either at harvest, or at an earlier stage of growth(the latter is obviously more useful for diagnostic purposes). The criticalconcentration is defined as that corresponding to a final yield which is 95%(say) of the ceiling yield.

1 Critical concentration Upper critical concentration

LI-

Deficient
range

Luxury range

Toxic range

Concentration of nutrient in tissue
Fig. 4. Relationship between yield and nutrient concentration in tissue at an
earlier stage of growth. The critical concentrations shown are for 95% of the
maximum yield.
27

However, there is a great deal of variation in published criticalconcentrations for each species and element (Chapman, 1966; Reuter andRobinson, 1986) and in view of the possible changes in nutrient supply
which might occur between leaf sampling and harvest, it seems likely thatleaf analysis results should be used for "diagnosis" of current growth, rather
than for "prognosis" for final yield (Scaife and Barnes, 1977).
Despite the above limitations, leaf analysis, if properly conducted, is themost reliable method of detecting nutrient deficiencies. The criticalconcentrations given in Table 2 are applicable to the "youngest fully
expanded leaves" of semi-mature plants of most species, but the reader isreferred to Reuter and Robinson (1986) for information on individual
species. Clearly, values which are well above or below the critical value will
give the most reliable diagnosis.

Tissue and sap tests
The concentrations given in Table 2 are for the total amount of eachelement in dry tissue, measured by any laboratory method which gives near
100% recovery. However, some nutrients are present in the plant in several
forms, notably as "raw materials" which are not yet assimilated (e.g. nitrate,sulphate, inorganic phosphate). The concentration of these ions varies much
more than those of the assimilated, organic forms, in response to changes inthe balance of supply and demand (Peck et al., 1974) and can thus bemeasured by much simpler, cruder techniques than are employed inlaboratories. In the 1930s these "tissue tests" or "sap tests" were already inuse in the USA (Carolus, 1936). In 1976, the firm E. Merck, of Darmstadt,
FRG, introduced nitrate test strips into UK, and these were found to be
useful for measuring the nitrate concentration in vegetable petiole sap(Scaife and Bray, 1977; BDH, 1984). In view of the great difficulties in
optimising crop nitrogen nutrition, several authors have since used thesestrips and attempted to establish critical sap nitrate concentrations forvarious crops. However, there has been rather little take-up of thesetechniques, and the reason is no doubt because of the difficulties posed byapparent variation in the critical concentration due to light intensity, age ofplant, etc. For example, Schrage (1990) showed that the sap nitrateconcentration of lettuce varied by as much as three-fold during five days,
whilst the soil nitrate hardly changed.
Nevertheless, the strips are useful for distinguishing between possible
causes of chlorosis, and if users and experimenters were willing to takereadings at dawn it might lead to greater reliability.

28

Diagnosticsprays
If a nutrient deficiency is suspected, individual elements (such as copperin the ADAS method mentioned above) or a "trace element cocktail" may be
sprayed onto the crop in patches, or better, long strips. If symptoms
disappear, or at least are absent in the new growth on the treated patches, but
not on the rest of the crop, this is the most certain diagnosis possible. It may
be too late to prevent yield loss in the current crop, but it should at least
confirm or disprove other methods of diagnosis, which is useful for future
crops. Even if no clear symptoms are apparent, it may be worth trying thismethod on a slow-growing crop, which may be in the "hidden hunger" zone.
To establish a meaningful yield difference between the treated and untreatedareas in the absence of any visible effect, however, would require the use of
rigorous statistical methods.
3.3. Soil analysis
Soil analysis has the obvious advantage over plant analysis that it can bedone before basal fertilizer is applied, and hence used to adjust the basedressing. Unlike plant analysis, where the total amount of each nutrient
element is usually extracted from the leaf (except as mentioned above), soil
analysis aims to imitate the plant by extracting only that fraction of theelement which is available to the crop. Having chosen a promising
extractant, the researcher has to show that the results correlate well with crop
response. This was done for phosphorus by Van der Paauw (1971) who usedwater as an extractant. Different extractants will remove quite different
amounts of nutrients from soils, so the grower or adviser must realise that it
is essential to check that the analytical method used is the same as the oneused to establish the criteria he is using to interpret the figures. Anotherprecaution is to ensure that the soil sample is truly representative of the
field: it should be made up of at least twenty subsamples, normally takenwith an auger to plough depth over the whole field. Special methods havebeen developed for nitrogen, as will be discussed later.

4. How much to apply, when, how, and in what form?
4.1. Nitrogen
4. 1.1. Estimating application rates
The optimisation of fertilizer nitrogen use has absorbed the attention ofvery many agronomists and others for at least a century.

29

Fig. 3 illustrates the extraordinary profitability of applying N to a highvalue crop such as cauliflower. If one knew exactly where the optimum lay,
there would be no problem, but because of the numerous transformations of
N in the soil, the effect of weather on these and on crop growth and hence N
demand, no system yet devised seems able to predict this optimum dressing
with an accuracy (i.e. a coefficient of determination, R2 , between prediction
and observation) much better than 30%. In the past, growers tended to "erron the high side" with N applications to avoid the risk of yield loss, but they
are now under pressure from all quarters not to do this, because it leads toexcessive nitrate in the produce and in the soil at harvest. This latter
eventually pollutes water sources, and the cost of removing nitrate fromwater is about US$ 15 (kg N)-' (Bums, personal communication).
The "Nitrogen Cycle" in soil (Fig. 5) is described in detail elsewhere(e.g. Mengel and Kirkby, 1987). Nitrogen in crop residues, organic manures,and the "old" organic matter in soil, is primarily in organic form (e.g.
protein) and as such it cannot be taken up by plants. It must be mineralisedby bacterial action, first to ammonia, then via nitrite to nitrate, in which
form the great majority of uptake occurs. Only some 2-3% of "old" organic
matter is mineralised each year, whereas vegetable crop residues are entirely
mineralised in any time from 10 d to a few months depending on species andthe temperature, moisture, and aeration status of the soil (Schrage, 1990).

The Nitrogen Cycle"Denitrification"
conversion to
N Gas

Fertiliser NCops
N inRainI
P

Los...
r

J2€FYM

DN

gas fixed by(tpeas,nodulo beans)bacteria

inorganic. 1Mineralisation
N
Immobilisation(Nitrate'Ammonia)

Leaching of nitrate(in drainage water)
Fig. 5. The nitrogen cycle.

30

FM

l

Soil organic
matter

These large quantities of rapidly-mineralisable residues are, from thenutritional point of view, the most significant feature of vegetable cropping(Table 4). In a survey of 132 farms in lower Saxony in spring 1977, Bdhmer(1980) found an average amount of soil mineral N (0-100 cm) of 78 kg/ha
after cereals, 185 after I year of vegetables, and 316 kg/ha after several
years of vegetable cropping.
Table 4. Fresh weight and nitrogen content of vegetable crop residues (after
Schrage, 1990).
Crop
Cabbage
Cauliflower
Broccoli
Kohlrabi
Lettuce
Leek
SpinachFresh weight, t/ha

% N in fresh wt

kg N/ha

65
55
66
I5
15
25
10

0.30
0.36
0.32
0.32
0.36
0.35
0.45

195
198
211
48
54
88
45

Once in the form of nitrate, the N can be leached through the soil profile.
For non-cracking soils, the rate of leaching through a soil layer can be fairly
well estimated by assuming that the water percolating through the layer
mixes thoroughly with that already in the layer: once field capacity is
exceeded, part of the water "overflows" to the next layer, taking with it acorresponding proportion of the nitrate (Bums, 1974). Needless to say,leaching is most severe when precipitation exceeds evapotranspiration, andwhen there little or no crop cover, as in a European winter, or in the humid
tropics. Other processes which may occur are denitrification, ammonia
volatilization (Terman, 1979), and ammonium fixation. The first is again amicrobial process, in which nitrate is converted via nitrous oxide to nitrogengas, rendering it useless to plants. It is promoted by anaerobic conditions,high temperatures, and high nitrate concentrations.
Ammonium-N, whether applied as fertilizer or occurring as an intermediatein mineralisation, can be lost if soil pH is above 7.2 (Barker, 1980).
Ammonium fixation is a form of cation adsorption which may "lock up"
ammonium nitrogen in large quantities if2:1 lattice clay minerals are present.
Unlike most nutrient elements, therefore, nitrate nitrogen in the soil isonly "buffered" in the sense that it may revert from the inorganic (mineral)
form to the organic form under certain circumstances. So excess nitrate not
only accumulates in the crop (see Fig. 6), but is leached out of the soil in
winter. It may also damage the current crop in various ways.
31

It is little wonder that so many attempts have been made to find ways of
optimising nitrogen dressings, and some of these will now be described.

1800
1600

W May 28

E 1400 -ENJune 9

L

June 17
June 23 (mature)

LL
1000
800
8600 --

c
0N
C)

CN

N

o, 600z

400 200
0

50

100

200

400

Nitrogen applied, kg ha- 1
Fig. 6. Nitrate concentration in spinach leaves at 4 sampling dates with 5
levels of applied N (applied as ammonium nitrate) (Scaife, unpublisheddata). Such a pattern is typical of all crops (although actual concentrations
differ from crop to crop - see Scharpf, 1991) and reflect a similar pattern of
nitrate variation in the rooting zone of the soil.

ADAS (UK Agricultural Development and Advisory Service) method
This involves categorising fields (0, 1, 2) according to the previous cropgrown, and adjusting N recommendations accordingly (MAFF, 1994). Index
0 thus represents a "low N residue" situation (e.g. cereals, sugar beet, poor
pasture) needing more N fertilizer than index 2 "high residues" (e.g. liberal
FYM, long high-N leys, lucerne). Index I is intermediate. The adjustments
are usually about 50 kg N ha-l for a unit change in the index, but they varywith crop and soil type.

32

The German "Nmin" system
This is based on work carried out by Wehrmann and his colleagues andstudents at Hanover University since the 1970s (Scharpf, 1991). The essenceof the method is that a soil sample is taken before applying the basal N
dressing, to the depth expected to be exploited eventually by the crop (0-30,
0-60, or 0-90 cm), and analysed for mineral N (NO 3N + NH 4 N). The total N
requirement (initial soil Nmin plus optimum fertilizer, kg ha-I) is termed the"Sollwert" (Target value). The N fertilizer requirement is calculated bysubstracting the mineral N originally present in the soil from the Sollwert.
Scharpf (1991) also gives tables of rooting depth for each species,
allowances for freshly incorporated crop residues, etc.
The "KNS"system
This is a development of the Nmin system, described by Scharpf (1991);
and Lorenz et al. (1989). Unlike the original Nmin system, it takes account of
the N mineralised during the growth of the crop. In its present form, it
involves soil sampling at least twice for Nmin determination. The firstsampling is made to 30 cm depth prior to basal N application, and enoughextra N is given to take the crop to the top-dressing stage. A second samplingis then made to the full crop rooting depth, and this time the amount found is"topped up" to the amount needed to carry the crop to maturity. Target
values are provided for both stages. In the Pfalz district of the Rhineland, thecost to the grower was subsidised until 1994 and there is a very quick
turnround time for the soil analysis. The system is being recommended in the
Netherlands for gherkins, fennel, leek, and lettuce (Soorsma, 1992).
Possible modifications to the KNS method
Soil sampling to these depths is arduous, and on some soils, quite
impractical. It can be argued that the first sampling in the KNS system is
unnecessary, provided that enough N is added to ensure the supply until the
top-dressing stage (the desirability of splitting N dressings has already been
mentioned). Since that stage should be at the beginning of the "grand periodof growth" (to permit the passage of the machinery without damage to thecrop) it follows that the total amount of N needed before then is very little.
However, it is frequently observed in fertilizer experiments with broadcast
basal N that an optimum level of about 100 kg N ha-1 is apparent when theplants are far too small to have used this amount (e.g. Scaife and Turner,
1984).This suggests that they are responding to the concentration of mineral33

N in the root zone, and that if this concentration could be achieved by"banding" or placing the N close to the plants, less would be needed at thisstage. Such techniques are used for maize in the USA, where a "Presidedress soil nitrate test" (PSNT) is being tried. The advantage of thisapproach is that the soil test measures mineral N after previous crop
residues, organic manures, etc., have had an opportunity to mineralise, andafter the main leaching danger is past. Furthermore, it should be easier toestimate yield potential at this stage than before planting. This idea was alsosuggested by Scharpf and Weier (1988) and Nmin sampling before topdressing is being practised in Denmark (Sorensen, personal communication).
Simulation models andExpert Systems
By the use of simulation models, it is hoped to avoid soil sampling
altogether. Such models ought to improve on tabular approaches to the
problem because they take account of the timing of events. For example,
cauliflower residues might be in organic form, and hence immune toleaching, one day, and almost entirely as nitrate, and thus susceptible toleaching, 10 days later. "User-friendly" versions of these models are now
being developed, which the grower can use as a day-by-day management tool.
Expert systems are computer programs which provide advice based on
numerous relevant factors, whilst not attempting to calculate growth, etc., ona daily basis (Fink and Scharpf, 1993).
Sap testing
Sap nitrate testing as a guide to N top-dressing has been tried (Scaife andTurner, 1987) but with disappointing results. There is no doubt that sap
nitrate concentration is a sensitive indicator of the N supply/demandsituation, nor that the commercially-available test strips are adequate for useon the farm. The problem has been to establish reliable criticalconcentrations for each growth stage. Some authors (e.g. Nitsch and Varis,
1991) appear to have had success with them.
The "Diingefenster"This is a German word meaning "fertilizer window" and refers to thenotion of leaving small marked patches of a crop with somewhat lessnitrogen than the rest of the crop. The idea is that as the crop "runs out" ofthe nutrient, these patches will be the first to show deficiency symptoms, andtherefore provide early warning of the need for a top-dressing.

34

It was tested on numerous vegetable species for nitrogen top-dressingsby Schrage (1990) who found that in most cases, the indication of deficiency
came too late to permit top-dressing with conventional machinery, andyields were therefore lower than with the "Nmin" system.
Conclusions regardingN prediction methods
Although most of these methods would appear to be eminently sensible,
they should be tested in extensive, preferably on-farm, field experiments toprove that they really work. When this has been done the results have often
been far from satisfactory. For example, Neeteson (1985) showed that for 77
potato experiments on clay and loam soils in the Netherlands, the Nmin
method was no better, as regards profit, than if a fixed recommendation of
245 kg N ha- t had been used on all sites. It did however result in an average
reduction of 40 kg N ha-' in the amount of N fertilizer needed. In view of
the importance of nitrogen optimisation, it is vital to know whether thesesystems do work, and if not, why not. Some possible reasons why theymight not are:- Failure to locate the true optimum in the fertilizer experiments,- Nmin sampling coincided with a short period of immobilisation,- Actual crop yield, and hence N demand, were not as expected,- Mineralisation between sampling and peak demand was not as
estimated,- Errors in Nmin analysis, or changes occurring between sampling andanalysis.
There is little doubt of the value of Nrin measurements when very highor very low values are found. Intermediate values are less useful.
Soil nitrate can be measured quite satisfactorily on the farm using
Merckoquant test strips and a reflectometer (Nitsch, 1984).
4.1.2. Choice of N-fertilizer
Materials available
Types of N-fertilizers which are used in vegetable growing and their N
percentage are listed below.
Ammonium fertilizers:- Ammonia (80% N), ammonium sulphate (21% N).
Nitrate fertilizers:- Calcium nitrate (16% N), sodium nitrate (16% N).

35

Ammonium nitrate fertilizers:- Ammonium nitrate (about 34% N), calcium ammonium nitrate, which is a
mixture of ammonium nitrate and calcium carbonate (21-27% N),
ammonium sulphate nitrate (26-30% N).
Amide fertilizers:- Urea (45-46% N), calcium cyanamide (20% N).
Solutions containing more than one form of N:- Urea ammonium nitrate solution (28-32% N).
Archer (1988) gives more information about these materials.
Ammonium sulphate has an acidifying effect on the soil and may be
useful on alkaline soils, or where sulphur is needed. Urea should not be usedon such soils, since large quantities of N may be volatilized as ammonia(Fenn and Miyamoto, 1981). Calcium nitrate, particularly when used as afoliar spray, has been shown to control various calcium-related vegetable
disorders (Maynard, undated). Calcium cyanamide ("Kalkstickstoff') may
limit the damage to Brassica crops caused by clubroot (Plasmodiophorabrassicae) (Mattusch, 1978). Other things being equal, the choice of N
source is governed by cost and convenience.
Nitrate versus ammonium
Apart from urea, these materials contain varying proportions ofammonium and nitrate nitrogen. Unless nitrification inhibitors (see below)
are used, ammonium is converted by soil bacteria to nitrate very quickly atneutral pH and favourable temperatures, so that most crops obtain most of
their nitrogen as nitrate.
Barker and Mills (1980) reviewed the pros and cons of nitrate andammonium use. Ammonium is absorbed onto the soil cation exchange
surfaces and cannot be leached, but it can be toxic (as when ammonia gas isevolved under alkaline conditions), or can compete with other cations suchas potassium and calcium, possibly causing physiological disorders, such as
tipbum of Chinese cabbage (AVRDC, 1985). Although some authors haveshown that a small proportion of ammonium-N can enhance yields of certain
crops (Ikeda, 1988), Barker concludes that the inclusion of ammonium inthe fertilizer needs to be carefully regulated. The presence of a certain
amount of nitrate can reduce the toxic effects of ammonia.

36

Slow release N-fertilizers
To reduce the risk of leaching and salt damage, various "slow-release" or"controlled release" nitrogen fertilizers have been developed over the years,
including Nitroform, or Ureaform (Urea-formaldehyde), "Gold-N" (sulphurcoated urea), "Osmocote" (resin-coated NPKMg + trace el. compounds),"Ficote" (polymer-coated compounds), etc. Some of these products are in
regular use for nursery stock etc., but for field-grown crops they are
generally too expensive, and indeed may be too slow for quick-maturingcrops (Lorenz et al., 1972; Kolota, 1984). Controlled-release N sources andnitrification inhibitors were reviewed by Prasad et al. (1971) and Maynard
and Lorenz (1979).
Nitrification inhibitors
Several materials such as nitrapyrin (N-serve), and dicyandiamide (Didin
or DCD) have been found to inhibit nitrification (Prasad et al., 1971), thus
keeping the N in the ammonium form, and reducing the leaching risk. Thisrisk is probably minimised more cheaply by using a split dressing of normal
N fertilizer such as ammonium nitrate (AN) (Kolota, 1984). There has also
been interest in inhibitors to reduce the nitrate concentration in vegetables atharvest time, which it may do (e.g. Venter, 1984), but the question arises as
to whether the residues of the inhibitor in the crop are any less harmful tothe consumer than the nitrate. According to Maynard and Lorenz (1979),
nitrapyrin has low mammalian toxicity and is not taken up by plants.
Aqueous ammonia, anhydrous ammonia and "ammonium-depots"
Aqueous and anhydrous ammonia appeared in the USA in the forties andtheir use in the UK increased rapidly in the sixties (Page, 1972) although it
was then only 1% of UK N use compared with 35% in USA and 18% in
Denmark. The raw material is cheap, but to avoid gaseous losses it must be
injected into the soil using special equipment, which is normally done bycontractors. Page et al. (1974) found that both forms were as effective as
ammonium nitrate for Brussel sprouts.
The "ammonium-depot" system was developed by Sommer (1991).
Localised zones of aqueous ammonia, with a DCD inhibitor, are placed near
the crop roots, which proliferate around them. The author reports 24
experiments with six vegetable species in which the depot system iscompared with calcium ammonium sulphate in split dressings. He found no
reduction in yield or quality, and a reduction in crop nitrate levels at harvest.

37

4.1.3. Methods of applying nitrogen
Single broadcast base dressing
All or much of the N for vegetable crops is often applied broadcast onto
the soil shortly before drilling or planting the crop, either as a "straight" N
fertilizer, such as ammonium nitrate (AN), or as a compound containing P,
K, etc. This is a cheap and simple approach, and has the advantage that withmoderate rainfall, the N should be fairly well spread through the rooting
zone by the time it is needed. If part of the N is in the form of ammonium(e.g. 50% in AN), this part is protected against leaching for a few weeks,
depending on soil temperature. "Spinners" or pneumatic full-width
distributors are used to broadcast the material, preferably just before seedbed
preparation.
Split dressings
Many growers split their nitrogen dressings into a basal application andone or more top-dressings (= side-dressings). Although there are reports(Everaats, 1993) which lend little support to this practice, there is every
reason to believe that it is sensible, because we know, for example, thatbasal N dressings of 100 kg N ha-1 or even less can be harmful, particularly
to drilled crops in dry conditions (Page and Cleaver, 1983). On the other
hand, one cannot omit the basal N dressing, because in moist seedbed
conditions the optimum N rate may be quite high (Greenwood et al., 1989).
There seems to be little justification for more than one top-dressing, and thebest time for this is at the beginning of the "grand period of growth" which
is roughly when broad-leaved plants are about 10 cm across. At that time itis still possible to get into the crop with machinery, and there is very little
danger of further leaching. A 50:50 split (base:top-dressing) is normallyappropriate. Unless rain is expected, top-dressing should be followed byirrigation to wash it into the soil and minimize leaf scorch. Late top-dressing
should be avoided as it increases the nitrate content of the crop.
Starter fertilizers, placement and banding
Seeds contain a limited reserve of nutrients which is sufficient for only
7-10 days' growth (Hole and Scaife, 1993). It is therefore essential toprovide a favourable nutrient environment around the germinating seed.
Costigan (1988) has shown that broadcasting may sometimes fail in thisrespect, and has reviewed the work done on placement at the National
Vegetable Research Station, UK (now HRI, Wellesboume) prior to 1988.

38

Fertilizer placement hiis been mtich used in tile ISA, espccia l for P and K
fertilizers (Randall atnd floe ft. 1)88) bt mUch less so in I urope. Cooke CI
a/ (1956) described tLK experiments %ith 8 Negetable species. most ofvl ich benefitted greatl from placement of IPK and NPK Recent ork , Ifh
onions and lettuce (Stone and Rose., 1992) shoied benefits of injecting 20
kg N ha-I as a solution of diammonium and illonOaImimOnlll phosphate
below the seeds, ev en wN
hen ample N. P and K had been broadcast (Plates 7
and 8) Lettce c icids were increased fron 5t ha- t on the control plots to 23
I ha- on the plots wNith 20 kg N ha-t as starter fistlifizer, representing an
uptake elficiency of about 2009%. (l[his mihil of course be due to theaccompanying P. but tile "primin" effect of N f'brtilivCr is a known
phenomenon: Jenkinson ct oU.. 1985).

v"e

Sl tu it N till titi iu/liticdl lto
p l c e lq u id ztild i/e r 2 5trim
tfl
t .'ccd I he stolIon
ilIII
ito i I n) Is titreev

bcl

102

h% inlul-heet-drien pistak
lic pump d own it vtbc ittaliched

to tle trailing cd el thetinc

on 1h lIi

LomIprC-thefi soil

Icd b the press Myikccl bcltc
Ith sed is drilled

l lice (it st~irtvt Iyitihtcr oi

vti1(11tS,1ii
ittv-lttld

-.ii

il

sl' tuetdidd vIetHi Il(11t 1P

tnd 60 k P ()5t hiNh~rimdcaist ii,,nlrillon/]osim wt ito
1

N hi

I)

,( butItitik" N

hl

TInI halrvcs,[

S

itebulbs %v al:,
ije-

,l20

I8 t i%itt
v%uk 91t ke N ha
/
a,I',

180

alflcr),t tti

1111P tre'd 'I vluaA ;tlllirte11/t59

(wher>pe(iwt.

1o111tiUticttol t

hiit\[Plans

tt+r,

It

tr

t2'5$ t& potl1t'te

tel yit il artiotturi

Nhizophere. and this helps twt keep the acctmlaritne(Stonie+pe rontll

tend io awciit
theP in solution. N itrate'ipt-ke genetill, eitlts at an increase in hivosphere pl (P,,latschtnct. IP6)Stnltetrtil/el can he used to >atist he NPK need, of the crop tw theitt Ionlth or soiol iltCl driiled crops [here xvould appea to be"'npieoable s.ope t combihirt tie teehultque x,,th the "KNS" (ir "PSNI"'
St \tetIit

to tlijtitlise N use.

Ilhe poblen , tith
top-drcssed \ is that ther. ma not be sufficient
raintall to xxash it into
the moil Fobair applic aion or lrttilizeTs is thouclit to
Ivoid this prioblen, burt (ioodig and !)aaies (I9092) consdeled that fir
toll" urea sptax- onl cereals, this question is tillopen. IheIC authors statethat the danger ot lc
et scorch is less mxillthaitbv, other tornlws of NIcitili.ers Although 15 kg N ha- isa It ue olten quoted as an appropriate
anlouu to ailppx as liar tted
re[at ~irhard and Literin (19S6) applied 100
kb N ha t as an NPK comn pound to the foliage of sexen ,cgetalbleecrops.
increasnme yields by 12-74"s %%ithout leaf damage.

42. Phosphorus
4.21 Applicat ion pliloso!h} ior P atd K
Ihtee ateo Ixo posiblte approache.s to P (and K) fertilization. [lie Iirst ist' "lertilii lot the crop" xviiich mncurs applying the amtioutt \xhich, On tihe
iasi s oft a ,ohI ndtmsts and the ktiovn Iespons cLharcteristics ol the cropalhout to b gto\\ n,x%ill he optimal for ptofit. The other it to "tetlilize lor thesoil". ie to appi a "maintenance dressiiitt P.tnot necessarily exT-,+ sear,t) keep the sotl P oncttratiotn at a Iee vhich is known to satisl th

requiremeits olfit tile crops in the rotatton. [his is done b replaciq the 1P
itctru ed beile crops. whici.

aks wme itax e seen. nomay be veor, u l ow Och[!
t1nt eld onI I o - sodil. Ihe second

ie l"totdcast dtessing gi\ ing aluinuim

approach i, pos,dle, because. unlike mineral N, P is stronlsg

held in the soil
bhoth by union exochlange and it+sparinhgl soluble orni) and is not,ignilicantl leached out fom tmineral soils) in the wointer
Although tihe
national ligures hit P and K in [able 8 x ould hnplx that'+luli/ing Ior tile
Crop'" is otlicialI,% ncottraled. most of woo correspondents
xxele inhavl,,r of the "llulintentance" approach+ w
xhich isobviousl, tihe
lIo!e

4,
0

convenient (Scharpf, Gysi, Sorensen, personal communication). Scharpf (forGermany) considers that a suitable long-term annual average for vegetable
farms is 60 kg P 20 5 ha-1 , which is in close agreement with the mean P
1removal of 15 species in the UK listed by Greenwood (1974a) of 55 kg ha- .
Gysi (for Switzerland) says that average P application should equal theexport, and is currently too much. The figure given by him (Gysi, 1993) for
the amount exported in 1990 from a 19 hectare mixed vegetable farm was
49 kg P 20 5 ha- 1. Sorensen recommends 70-90 kg P2 0 5 ha- I for vegetables
grown in Denmark on soils of medium P status.
In the past, vegetable growers in the UK and elsewhere in Europe haveadded more P than was removed, and soil P indices have risen to very highlevels as a consequence. By maintaining these high levels, they may hope to
avoid the risk of P deficiency even in highly responsive crops such as
spinach and lettuce. Costigan (1985) has shown that this may not be so,
because these crops require a very high soil solution P concentration soonafter emergence. Alt (1984) summarised the results of 24 P/K/Mg
experiments with twelve species grown over 15 years at Osnabrulck, andshowed that the average optimum level of P20 5 was 104 kg ha- 1, whereas
the amount removed in the edible parts was only 44 kg ha - I . This might
explain why growers add more than is removed, and lends support to the useof P-containing starter fertilizers, which satisfy plant demand with minimal
quantities of P. The question is whether there any disadvantage, either forthe grower or for the environment, in maintaining a very high soil P status.
According to Mengel and Kirkby (1987), very little P is leached frommineral soils, but there is a danger that on certain soil types P will be "fixed"
i.e. rendered unavailable by conversion to insoluble forms such as apatite. P
can be leached from peat soils and this is creating a eutrophication problem
in the Florida Everglades (Espinoza et al., 1993). It is the element causing
most eutrophication, and although the major source of P in rivers is ofdomestic and industrial original, surface soil runoff is undoubtedly also
responsible (Sharpley and Menzel, 1987). On some soils the use of excessive
P can run the risk of inducing zinc deficiency (Mengel and Kirkby, 1987).
4.2.2. Phosphorus fertilizers
The materials most used, and their P 20 5 percentages are:Water-soluble types (quick-acting):- single superphosphate (18-20% P 20 5 + 11-14% S);- triple superphosphate (45% P20 5).
- ammonium phosphates:41

* monoammonium phosphate (11% N, 52% P2 0 )5* diammonium phosphate (18% N, 46% P20 5)* ammonium polyphosphate (10-15% N, 35-62% P 025).

Partly water-soluble types (quick- and slow-acting):- partly acidulated phosphate (23-26% P20 5 at least one-third water-soluble).
Slow-acting types:- dicalcium phosphate (citrate-soluble; 40% P20 5).
Very slow-acting types:- rock phosphate (finely-powdered soft type, e.g. 30% P20 5), with reactivity
indicated by formic acid-solubility; permitted minimum is about one-halfof total P2 0 5 content).
Follett et al. (1981) and Archer (1988) give further details. The great
majority of fertilizer P is applied as NPK compound fertilizers (which
chemically are mixtures), in which triple superphosphate (monocalcium
phosphate) is the main P-containing ingredient. The use of rock phosphatecannot be recommended for vegetable crops because of its low solubility(Khasawneh and Doll, 1978). The same applies to all other slow-acting
forms. Single, or normal superphosphate contains sulphur ( as gypsum) andis therefore valuable where this element may be deficient.
4.2.3. Methods of applying P
By now it should be clear that, if it is feasible, it is desirable to place P,
preferably in company with some ammonium, e.g. as ammonium phosphate,near the young seedling. It this is not possible, the next best option would
appear to be to apply the maintenance P dressings in large doses for the P
responsive crops in the rotation, with none for the others.

4.3. Potassium
4.3. 1. Amounts of K to apply
As with P, K is strongly adsorbed onto soil colloids and the response ofindividual species is not related to the amounts they take up (Greenwood etal., 1974a). Thus, the same approach, that of applying "maintenancedressings" equal to offiake, is recommended in most countries. Scharpf(personal communication) suggests 200 kg K 2 0 ha- 1 as an average annual
dressing for German conditions with high yields: in Switzerland, Gysi's 19
ha farm showed an average annual removal of 141 kg K 20 ha-1 .
42

For a more precise calculation of the average annual dressing of K to
apply, the reader should refer to Table 9, from which it is possible, byconsidering the proportion of different crop species in the rotation, andmaking appropriate adjustments for yields actually obtained, to arrive at an
average annual K dressing which closely balances the K offtake.
However, the question arises with the maintenance approach "what levelof soil K should I maintain?"; i.e. before settling down to a programme
which replaces the K sold off in the crop, should one increase or decrease
the soil K status by applying more or less than the "offtake" amounts forseveral years in order to establish a higher or lower soil K status than alreadyexists? If very high levels are maintained, it is likely that crops will take up"luxury" amounts of K, as vegetables readily do, and this is wasteful.
Furthermore, it will increase the risk of K leaching, as it can on light or
peaty soils (Mengel and Kirkby, 1989). On the other hand, if very low soil K
levels are maintained there is a possibility that the more responsive crops,
such as spinach, (which apparently has a high K intensity requirement)
might not achieve maximum yield when the maintenance dressing is applied.
Little is known about the K intensity requirements of different vegetablespecies, but the NPK predictor (NVRS, 1980) was intended to try to throw
light on this problem by providing an estimate of the responsiveness ofnumerous vegetable species when grown on soils of varying N, P, or K
status. It was based on the work of Greenwood et aL (1974a). Table 5 shows
the predicted percentage of maximum yield (i.e. that obtainable with
optimum K fertilizer) which 19 vegetable crops might be expected to giveon soils at three levels of K status, when not given any K fertilizer. The
crops are ranked in increasing order of responsiveness. If a rotation consistsof crops near the top of the list, one can allow the soil K level to fall to as
little as 60 mg K 1-1 (measured by the ADAS method, using ammonium
nitrate as extractant) whereas if it includes crops at the bottom of the list, soil
K levels should exceed 150 mg 1l.If responsive and non-responsive crops
are to be grown in rotation, large amounts of K should be applied for the
responsive crops, with less, or none, for the non-responsive ones, so that the
average annual dressing balances the average annual offtake.

43

Table 5. Percentage of maximum yield expected from various vegetablespecies when grown on soils of different K status (derived from NVRS, 1980).
Available* soil K<60
60-150>150----- --------------mg I-1 - - - --- - - - - - - Calabrese
100
100
Pea
98
98
Winter Cabbage
95
98
Swede (Rutabaga)
95
98
Summer Cabbage
95
98
Brussels Sprout
95
98
Lettuce91
98
Red beet87
98
Carrot83
95
Parsnip
83
95
Broad bean
80
95
Leek
80
95
Potato77
91
Dwarf bean
75
91
Onion
75
91
Radish75
91
Cauliflower
72
87
Turnip58
80
Spinach34
53
ADAS method K extracted by ammonium nitrate.

100
100
100
100
100
100
98
98
98
98
98
98
98
98
98
98
95
91
75

From the work of Alt (1984), it seems that the optimal dressing of K for
most vegetable crops is much closer to the maintenance dressing than is thecase for P, suggesting that there is no particular benefit to be expected fromboosting K concentrations near the plants by means of placement.
4.3.2. Potassium-containing fertilizers
Apart from some low grade unrefined products, all substances used as
potash fertilizers are high analysis products, water soluble and quick-acting.
They can be grouped as:
Cl-containing potash fertilizer:- potassium chloride or muriate of potash - MOP - (40-60% K20), the lower
grades provide Na in addition to K2 0 and with or without Mg.
44

Cl-free potash fertilizer:- potassium sulphate - SOP - (50% K 20; 18% S)- potassium magnesium sulphate (30% K 20, 18% S, 6% Mg).
4.3.3. The best potash fertilizer and methods of application
Chloride or sulphate ofpotash?
The main choice is between chloride and sulphate of potash. Zehler et al.
(1981) summarised research comparing the two forms of potash fertilizers.
According to them, SOP is to be preferred due to its advantageous side
effects if:- sulphur application is needed (low S-supply from the soil and highsulphur requirements of the vegetable crops as for instance, thosebelonging to the family Cruciferae);- chloride-sensitive vegetables are grown, i.e. french beans, broad beans,
onion and chillies;- vegetables are grown which are chloride neutral but prefer sulphate,i.e. tomato, radish, kohlrabi, cauliflower, spinach and peas;- soil salinity is a problem, because sulphate has a lower "salt index" perion of K (Yadav and Tomar, 1990);- very high rates of fertilizers are used as in intensive vegetable growing;- quality parameters are favoured by sulphur (chap. 4.4.3.).
The majority of K is applied as compounds which are available in thechloride-containing and chloride-free form. The use of both potassium
chloride (MOP) is common if no restrictions due to undesirable side effectsof this type of K fertilizer are expected and the sulphur supply of the soil isabundant.
The sodium-containing sources are useful for those crops which respondto it (see 4.4.4.).
Methods of application
It is generally agreed that K fertilizers are best broadcast onto the soil
and worked in before planting. This can be done in the autumn if necessary
except on organic or sandy soils, through which some leaching can occur.
Placement is not generally advisable: in particular potassium chloride cancause salt damage to germinating seedlings. If potassium is to be placed near
the seeds, SOP should be used.

45

Top-dressing of K salts, particularly on clayey soils, is unlikely to beeffective because of adsorption of K very near the soil surface.
Split application should only be considered if highly responsive
vegetables are to be grown on soils low in available potassium and low
sorption capacity.

4.4. Secondary nutrients4.4. 1. Calcium-related physiological disorders
There are several physiological disorders of vegetable crops which arethought to be due to a localised deficiency of calcium in the tissues. These
are tipburn of lettuce (Collier and Tibbits, 1982) (see Plate 5) and cabbage,internal browning of Brussels sprouts (Maynard and Barker, 1972), andblackheart of celery (Geraldson, 1954) and chicory.
Each is a form of necrotic breakdown of young leaf tissue. Their severity
is influenced by such factors as soil compaction, irregular irrigation, rapid
growth, and cation antagonism. The last-named may be the chief cause in
the case of tipburn of Chinese cabbage, which is now said to be a kind ofammonia toxicity (AVRDC, 1985). In the case of iceberg lettuce thepractical solution in the UK has been the adoption of the tipburn resistantvariety Salinas from the USA. Use of resistant varieties also seems to havelargely eradicated internal browning of Brussels sprouts. In Florida, thedisorders have been overcome by the use of high quality (i.e. low salinity)
irrigation water, and appropriate nutritional practices (Locascio, 1987).
4.4.2. Magnesium deficiency
It is usually considered that there is very little "hidden hunger" zone formagnesium, which means that there is no need to worry about Mg deficiency
unless symptoms are seen. These can be very striking in brassicas (Plate 3).
The diagnosis should be confirmed by leaf analysis, and immediate treatment
is possible by foliar sprays every two weeks of 2% Epsom salts(MgSO 4 .7H20) at 500-1000 I ha- 1 (a suitable wetting agent should always
be included in foliar feeds). However, this should only be used as an
emergency measure: for future crops either magnesian limestone (10% Mg),
Kieserite (16% Mg; 23% S), Epsom salts (10% Mg) or other Mg-containing
fertilizers should be incorporated into the soil, either at the rate recommended
for the next crop, or as a "maintenance dressing" of 15-20 kg ha-1 year-t .

46

4.4.3. Sulphur
Certain vegetable crops, notably crucifers, have a high sulphur
requirement, and since atmospheric levels of sulphur dioxide have beenfalling, we are beginning to see cases of sulphur deficiency in these andother crops. Apart from its effect on yield, sulphur is an important
contributor to flavour in brassicas (Freeman and Mossadeghi, 1972) andpungency in alliums (Freeman and Mossadeghi, 1970). Growers,
particularly of these crops who farm well away from industrial centres,
would be well advised to carry out periodical leaf samplings, and if S
concentrations fall below 0.35% (in d.m. of young leaves) they should use
sulphur-containing fertilizers, such as single superphosphate or sulphate ofpotash. The concentration of sulphate-S in rainfall varies from 0.5 to 4 mg S
I-I depending on the distance from industrial centres (Zehler et al., 198 1).
4.4.4. Sodium
It is doubtful whether sodium is essential for any higher plants, but
sodium can beneficially replace part of the potassium for crops of the family
Chenopodiacae (beets); also turnips, celery, and carrots (Archer, 1988). In
the UK, ADAS recommends the use of 150 kg Na ha-1 for carrots, and areduction of 60 kg ha- I in the K 20 dressing on light soils: for celery, on all
soils except fen peats and silts, the same amount is recommended without
reduction in the K application. The salt must be ploughed in at least a month
before sowing. There are also reports of sodium improving the flavour ofroot crops e.g. swedes (Truog et al., 1953). Na may be applied either as
sodium chloride, as Chilean potash nitrate (9-18% Na), Kainit (9-18% Na),
Sylvinit (25-28% Na) or sodium nitrate (26% Na). A sufficient amount may
also be present in irrigation water, and in rain (especially near coasts).

4.5. Micronutrients (trace elements)
Vegetable growers are often familiar with one or two micronutrient disorders (e.g. manganese deficiency in Eastern England), but they are easily persuaded that there may be others present in a symptomless form, which may
be reducing yield or quality. The cost ofapplying a "cocktail" spray, containing
several micronutrients, is seen as a cheap insurance against this risk.
To such growers the best advice would seem to be:- Have a complete leaf analysis done: if the results are well above thecritical values (Table 2), and the crop looks healthy, a response is mostunlikely,47

- If you do decide to spray, leave two or three clearly marked untreatedstrips for comparison.
Certain vegetable growing areas are subject to numerous micronutrient
deficiencies: such a one is Florida. The history of the discovery andcorrection of these problems has been related by Locascio (1987) andLocascio and Fiskell (1987).
If particular deficiencies or toxicities are diagnosed (see Table 3), thefollowing treatments are recommended:- Iron (most unlikely): if induced by other heavy metals (e.g. fromslurry), spray crop with .05% Fe EDTA at 500-1000 1 ha-1 .
- Manganese: spray with manganous sulphate at -10 kg ha-1 in 500 I ofwater every two weeks. Soil Mn application is not considered effectivein the UK, because Mn is precipitated at high pH. On Florida histosols,
Mn included in broadcast fertilizer is effective if pH is below 6.5:
above this pH, band placement of Mn below the drill is effective(Sanchez et al., 1989).
- Zinc deficiency: apply zinc sulphate (ZnSO 4 .7H20). at 5 kg ha-1 as ahigh volume foliar spray. See "Zinc in Crop Nutrition (undated)" forfurther details.
-Copper deficiency: apply copper sulphate (CuSO 4.51-120) to soil at 60kg ha-1 . Such a dressing should last for 10 years. See Shorrocks andAlloway (undated) for details.
- Boron deficiency: foliar spraying with "'Solubor" at 10 kg ha-1 ispossible but usually too late if symptoms already present: otherwise use
a boronated fertilizer or apply Solubor or borax to soil to supply 2 kg B
ha-t during seedbed preparation. See Shorrocks (undated).
- Molybdenum deficiency: for cauliflowers only: drench transplants with
a 0.03% solution of sodium or ammonium molybdate before planting
out. Seed treatment with 35 g of sodium or ammonium molybdate ha-1
is also feasible. Maintain correct soil pH.
- Manganese and aluminium toxicity: do not allow soil pH to fall below
6 (5.5. for peat soils).

4.6. Soil pH adjustment
Soils should never be limed without carrying out a pH measurement, or
better, a proper lime requirement measurement on each field to be limed, oreven on separate parts of fields. A lime requirement test takes into accountnot only the pH, but the amount of lime needed to bring about a change of48

one pH unit, which differs with the clay and organic matter content of thesoil. For mineral soils the aim should be to keep the pH near to 6.5: for peatsoils, 5.8 (Archer, 1988). If this is done, there will be a satisfactory supply of
Ca to the roots, but this does not ensure the absence of physiologicaldisorders (see 4.4.1.). Above pH 7 there is an increasing risk of traceelement deficiencies. The acceptable pH range for most vegetable species is5.5-7.0. For peas, broad and French beans, celery and lettuce, it should not
be below 6: cabbage, chicory, mustard, parsnip, swede and turnip cantolerate values just below 5.5 (MAFF, 1994). If clubroot is present, pH for
brassicas must be above 7. All these values refer to water extraction: if
CaCI2 extraction is used, pH values will be about 0.5 units lower. Table 6
shows the amounts of ground limestone needed to adjust the pH of different
soil types. It takes several months for liming to thoroughly correct the pH:much longer on very acid soils or with coarsely ground liming materials.
Table 6. Limestone (t ha-') needed to change the soil reaction of the plough
layer (adapted from Lorenz and Maynard, 1988).
Change in
pH needed*

Sand

Sandy
loam

Loam

Silt
loam

Clay
loam

Peat
(muck)

14
11
9.4
7.8
5.6
2.9
4.0-6.5
11
9.4
7.8
6.5
4.7
2.5
4.5-6.5
7
7.4
6.3
5.2
3.8
2.0
5.0-6.5
3
5.2
4.5
3.8
2.9
1.3
5.5-6.5
0
2.7
2.5
2.0
1.6
0.7
6.0-6.5
For peat soils, the target pH is 5.8.
N.B. If burned lime, hydrated lime, or dolomitic limestone are used, theamounts required will be 64%, 82%, or 86% respectively of the amounts
shown here.
Large pH adjustments with high amounts of lime have to be avoided. A
step-by-step approach is recommended.
Soil pH can be reduced by the use of elemental sulphur. The quantity
needed to lower pH from 7.5 to 6.5 varies from 500 kg ha-t on sands to1000 kg ha-1 on clays (Lorenz and Maynard, 1988). Sulphur has also beenband-placed to reduce pH locally below the seed (Sanchez et al., 1989).
On many soils, especially tropical oxisols, aluminium toxicity, and theeffect of soil aluminium on P uptake, are critical factors governing liming
practice. These questions have been discussed in detail by Haynes (1984).

49

The materials used for liming are ground or screened limestone ormagnesian limestone, ground or screened chalk, sugar beet or waterworks
lime sludge, and burnt or hydrated lime. The neutralising value of thesematerials varies from about 20% of that of pure CaO for the sludges, to 8095% for burnt lime (see Archer, 1988, for more details).

5. The organic approach
So far, nothing has been said about organic materials or organic farming
methods. A feature of vegetable farming is that it produces large quantities
of very valuable crop residues.
On commercial farms, they are usually ploughed in where they grew. It
seems to have been only recently realised that the "softer" of these residues
are decomposed within a very few weeks at summer soil temperatures(Schrage, 1990) and their N, P and K content (roughly 3, 0.3 and 2% of their
dry weight) should be available to the following crop, unless winterintervenes in which case much of the N may be lost by leaching.
Bulky organic manures, in which we will include cattle and pig slurry
and sewage sludge, must be returned to the land in the most effective way,
and their nutrient content allowed for. These contents are shown in Table 7.
For P and K, one can calculate the amounts being returned from this table
and count these towards the "maintenance" amount of roughly 60 kg P2 0 5
ha -1 and 200 kg K20 ha - 1 already mentioned as typical offlakes in intensive
vegetable production. For nitrogen, the position is more difficult because therate of mineralization of these bulky materials is rather unpredictable.
Typically, organically grown crops are likely to suffer from a deficiency ofnitrogen in early growth (Keipert et al., 1990) and a surfeit of it towards
harvest. Hence it should not be imagined that such crops will necessarily be
low in nitrate: the opposite sometimes happens.
The "biodynamic" method of organic fruit and vegetable production wascompared with "conventional" production in large-scale trials from 1977-85
by Keipert el al. (1990). They found that the method was more expensive,
more labour-demanding, lower-yielding, and more prone to failure thanconventional methods. They stated that there were no significant differencesin quality from the two methods.

50

Table 7. Typical nutrient content of animal manures (from MAFF, 1994).
Available nutrients
Total nutrientsDM% Nitrogen Phosphate Potassium Nitrogen 4 Phosphate Potassium
kg/t
kg/t
Fresh FYM 2
4.8
2.1
1.2
8.0
3.5
6.0
25
Cattle
3.0
4.2
1.4
5.0
7.0
7.0
25
Pig
kglt
kg/t
Poultry manures
6.8
7.8
5
9.0
13
15
Layer manure 30
14
15
10
18
29
25
Broiler/turkey 60
manurekg/m 3kg/m 3Slurries
3
3.2
0.60
I
3.5
1.2
3.0
6
Dairy
Beef 3
6
2.3
1.2
2.7
0.7
0.60
2.4
Pig 3
6
5.0
3.0
3.0
2
1.5
2.7
next
crop.
Notes: I Nutrients that are available for utilization by the
2 Values of nitrogen and potash will be lower for FYM stored in the
open or for long periods.
3 It is common for farm slurries to contain approximately 6% DM.
Slurries of DM% other than 6% will have greater or lesser
concentrations of nutrients than those shown above. Undiluted
slurry will usually contain approximately 10% DM.
4 This column refers to spring application. See the source reference
for more details.
Vogtmann et al. (1992) compared the use of "biogenic waste compost"
and farmyard manure compost, both supplemented or not with concentratedorganic NPK fertilizers, with inorganic NPK materials for cabbage andcarrots. Inorganic NPK (120-240 kg N ha-1 including Nmin) gave the highest
yields but also (in cabbage) much the highest crop nitrate concentrations. As
regards post-harvest quality and sensory properties (not described) thecontrol (no fertilizer) and other low-N treatments ranked highest.

6. Vegetable nutrition and crop quality
Nitrogen
Nitrogen is necessary to produce plants of suitable size for the market:
without it, growth is slow and the produce may be tough.
High nitrogen supply normally lowers the sugar content of plants, andzero-N plants are sometimes noticeably sweeter than the others (Plate 1).
51

N top-dressings increased bitterness in Brussels sprouts (Scaife andTurner, 1985) which suggests an increase in the content of certain
glucosinolates (Fenwick et al., 1983). Fischer (1992) showed that, forkohlrabi, volatile flavour compounds were maximised by a low-N moderateK regime. The bitter taste of purde from cooked beetroot grown with highnitrogen is due to pyrrolidone-carboxylic acid (PCA) derived from glutamine(Shallenberger and Moyer, 1958). According to Wedler (1985), high N
reduces storability of carrots, cabbage and dwarf beans, and impairs theflavour of carrots, celery and cabbages. It increases the nitrate concentration in
the produce (Maynard el al., 1976), which has been suggested as a possible
cause of stomach cancer (although the bulk of evidence would discount thisview; Forman et al., 1985); and is undesirable in baby food because of thedanger of methaemoglobinaemia (Maynard el al., 1976). Nitrate is anoxidising agent and can cause detinning of cans (Maynard el al., 1976).
Excessive nitrogen is also implicated in several physiological disorders,such as hollow stem of cauliflower (Scaife and Wurr, 1990) and black
midrib of stored cabbage (Berard, 1990). There is general agreement among
growers that it leads to softer growth. It exacerbates splitting, forking andbolting of carrots (Batra and Kalloo, 1990).
The effects of nitrogen on vitamin content of vegetables are variable andsmall compared with the effects of other factors. High nitrogen usuallydepresses the ascorbic acid content (Sorensen, 1984), but other vitaminlevels are sometimes increased (Miller et al., 1956).
Rather little information about the effects of K on crop quality isavailable relating specifically to field vegetables. The subject was reviewed
by Cummings and Wilcox (1968). They stated that most quality characteristics improved with increasing K over the same range as led to yield increase,and cited work showing that the amounts and proportions of organic acids,
but not their actual chromatograms, are profoundly affected by K. They
pointed out that the characteristic symptoms of K deficiency, namely
marginal necrosis of leaves, may affect the quality of leafy vegetables;
however, this would apply only in cases of fairly extreme deficiency. In
general, K is known to be important for turgor and the strength of stems, etc.
In the same book, Lucas (1968) drew attention to the adverse effects ofexcessive K in increasing the incidence of calcium-related physiologicaldisorders, such as blackheart, brown checking, and magnesium chlorosis ofcelery, and internal tipburn of cabbage. On the other hand, Peck and Stainer(1970) reported a reduced incidence of internal black tissue in late cabbage
with increasing K application. There is considerable evidence for fruit crops
and tomatoes, reviewed by Tsai-fua (1975), that high potassium depresses

52the uptake and translocation of calcium. Other such disorders werementioned in section 4.4.1. It is generally agreed that it is the percentage
saturation by K of the cation exchange capacity of the soil, rather its
absolute value, which would indicate a danger of such antagonistic effects.
As a general principle, the deficiency of one nutrient element will resultin other elements accumulating in crop tissues, often in the inorganic form.
Thus, He el aL (1994) have shown that increasing K applications to cabbage
up to 150 kg K 20 ha- I (which was optimal for yield) reduced its nitrateconcentration by about 50%.

Other elements
The importance of sulphur and sodium for flavour have been referred toin paras 4.4.3. and 4.4.4. respectively, and calcium-related quality problems
in para 4.4.1. Truog et al. (1953) found that celery grown with sodium had abetter (milder) flavour and was less stringy than when sodium was not
given.

7. Interaction with pests, diseases, and environmental stressThis was a subject of an IPI Colloquium held in Turkey in 1976 (IPI,1976). In the opening session, it was observed that there was a shortage of
information on these interactions, probably because of the lack ofcooperation between plant nutritionists and plant pathologists.
The proceedings contain very few references to vegetable crops, but
certain general observations may be relevant. High nitrogen levels appeared
to increase susceptibility of plants to obligate parasites, such as rusts,
mildews, clubroot and viruses, but it tended to reduce susceptibility tofacultative ones such as those causing necrotic leaf spots. Nitrogen form wasimportant, ammonia being toxic to certain soil pathogens, and nitrate toothers (Huber and Watson, 1974). These two forms can also have opposite
effects on the same disease. Potassium generally increased resistance todisease, e.g. soft rot symptoms in brassicae (Leuchs, 1959) but in carrots it
increased susceptibility to Centrospora acerina (Roll-Hansen, 1974). It helps
to protect plants from environmental stresses, and of these, freezing isparticularly important for temperate vegetables. Beringer and Trolldenier53

(1978) have reviewed the effects of K on frost and drought resistance, which
are physiologically related. See Perrenoud (1990) for a recent review ofpotassium effects on plant health. Calcium appears to have a protective
effect against several diseases (Kiraly, 1976). Hahn (1985) reported greater
susceptibility to fungal and bacterial pathogens for boron deficient vegetable
crops in the (then) GDR. Graham and Webb (1991) have reviewed theeffects of micronutrients on disease. They conclude that the effects are
generally beneficial, at least over the deficiency range of the element.
As regards pests, mention has already been made that low-N brassicas
appeal to pigeons. It might be thought that such plants, which contain highsugar levels, would also favour aphids, but Jones (1976) listed several cases(including peach and cabbage aphids on Brussels sprouts) in which N either
increased aphid severity, or had no effect. He also cited many instances whereorganic matter incorporation had beneficial effects as regards pest attack.
In general, it appears that well-balanced mineral nutrition, such as leads
to maximum yields but without luxury consumption, helps the growth of thecrop to keep ahead of that of pests and diseases.

8. Crop specific fertilizer management and recommendations
8.1. Vegetables grown under temperate conditions
Table 8 shows recommendations currently in use in several countries forthe major field vegetable crops grown: most correspondents pointed out that
there is no official national set of figures. In Germany, for example, thevarious "Lander" (states) may have different systems, as is the case with theUSA. Phosphate, potash, and magnesium recommendations mostly apply tosandy loam soils with "medium" levels of soil P, K, and Mg.

54

Table 8. Fertilizer recommendations for temperate vegetables in various
countries (wherever there is a blank space, it means that no information isavailable).
8.1. Amaryllidaceae
P20 5CountryN

Denmark
FinlandGermany
Netherlands
NorwayUK
USA
SwedenSwitzerland

240*
100
220* (60)
270*
170
100
125
170
120

kg ha-

K20

Mg

Leek (Allium ampeloprasum L. Porrum group)

240
145
240
200
200
125
170
195
180

90
150
70
75
135
150
170
105
60

30
20
60
0
30

Onion (Allium cepa L. cepa group)

Denmark
FinlandGermany
Netherlands
NorwayUK
USA
SwedenSwitzerland

135*
70
160* (60)
110
170
60
100
120
80

90
150
90
75
135
150
140
125
40

N

P20 5

220
100
250
150
200
125
140
195
200

25

K 20

Mg

20
60
0
40

8.2. Gramineae
Country

kg ha- 1

Sweet corn (Zea mays var. Rugosa Bonaf)

UK
USA
SwedenSwitzerland

75
155
140
120

50
135
80
60

50
135
160
180

0
30

55

8.3. Liliaceae
CountryN

Germany
UK
USA
SwedenSwitzerland

P2 0 5kg ha - I

K20

Mg

Asparagus (Asparagus officinalis L.)
90* (90)
50
230
50
75
25
60
140
140
30
80
30
120

20

N

Mg

15

8.4. Chenopodiaceae
Country

P20 5

Denmark
FinlandGermany
NorwayUK
USA
SwedenSwitzerland

K2 0
kg haRed beet (Beta vulgaris var. Esculenta L.)
200*
80
240
70
80
110
250* (60)
70
260
110
80
200
200
100
200
100
110
110
150
115
230
120
50
220

Germany
Netherlands
UK
USA
SwedenSwitzerland

195* (30)
240*
100
125
100
100

56

Spinach (Spinacea oleracea L.)
45
245
75
200
200
200
140
140
105
195
40
150

30
35
0

70
15
60
0

15

8.5. Compositae
P20 5

K20

Mg

CountryN

Germany
Netherlands
Switzerland

Endive (Cichorium endiva L.)
20
250
40
180* (60)
60
100
125
165*
30
180
50
100
Witloof (Chicory, Radicchio) (Cichoriunz intybus L.)

Germany
Netherlands
UK
Switzerland

80* (60)+75
0Denmark
FinlandGermany
Netherlands
NorwayUK
USA
SwedenSwitzerland

170*
100
140* (30)
150*
110
150
80
100
80

kg ha- I

190
50
150
50
150
150
150
50
Lettuce (Lactuca saliva L.)
180
70
100
80
150
40
150
125
150
135
100
250
170
170
135
70
100
30

25
60
0
30
15
12
60

10

8.6. Cruciferae
Country

Finland
NorwayUK
SwedenDenmark
FinlandGermany
Netherlands
NorwayUK
USA
SwedenSwitzerland

N

P2 0 5kg ha- I

K 20

Mg

Swede (Rutabaga) (Brassica napus L. Aapobrassica group)
180
90
110
150
60
75
0
150
50
50
200
105
140
Cauliflower (Brassica oleracea L. Botrytis group)
25
240
90
280*
110
60
145
25
300
90
300* (60)
60
200
75
300*
240
80
240
0
125
75
200
140
140
140
195
90
180
30
180
50
130
57

8.6. Cruciferae (continued).
CountryN

Denmark
FinlandGermany
NorwayUK
USA
SwedenSwitzerland

275*
200
350* (90)
240
250
140
250
220

Denmark
Germany
NorwayUK
Switzerland
Germany
Switzerland
Denmark
Germany
UK
USA
Switzerland
Denmark
FinlandGermany
NorwayUK
SwedenSwitzerland
NorwayUK

58

P2 0 5K 20
Mg
kg ha- I
Cabbage (Brassica oleracea L. capitata group)
90
115
50
80
75
140
140
80

305
170
190
240
175
140
290
300

30
25
0

60

Brussels sprouts (Brassica oleracea L. Gemmifera group)
250*
90
265
30
250* (90)
140
370
30
170
80
240
250
75
125
0
160
60
200
20
Kohlrabi (Brassica oleracea L. Gongylodes group)
200* (30)
80
210
15
120
60
180
50
Broccoli (Calabrese) (Brassica oleracea L. ftalica group)
220*
90
240
25
300* (60)
70
200
25
200
60
75
200
140
140
140
40
170
20
Chinese cabbage (Brassica rapa L. Pekinensis group)
200*
70
220
20
130
70
120
250* (60)
70
230
20
110
80
150
250
75
175
180
115
230
120
60
200
30
Turnip (Brassica rapa L. Rapifera group)
110
60
150
50
50
150
0

8.6. Cruciferae (continued).
N

Country

P20 5

kg ha- I

K2 0

Mg

Radish (Raphanus sativus L.)

Germany

100* (30)

40

180

20

NorwayUK
Switzerland

75
25
40

60
25
20

100
100
80

20

N

P20 5

K 20

Mg

8.7. UmbelliferacCountry

Denmark
Finland
NorwayUK
USA
Denmark
Germany
Netherlands
NorwaySwitzerland
Denmark
FinlandGermany
Netherlands
NorwayUK
USA
SwedenSwitzerland
GermanyUK

kg ha"1Celery (Apium graveolens L. var. dulce (Mill.) Pers.
25
220
90
230*
120
90
110
200
100
110
300
125
75
200
200
154
(Mill.) Gaud-Beaup.
rapaceumvar.
Celeriac (Apium graveolens L.
40
280
90
250*
20
330
140
220* (60)
60
200
125
220*
240
135
170
30
200
50
130
Carrot (Daucus carota L.)
30
240
80
120*
170
115
100
21
230
70
100(60)
60
200
125
80*
200
100
110
150
150
25
It0
110
75
240
105
90
40
220
60
130
Parsnip (pastinaca sativa L.)
30
300
80
0
150
75
75
Parsley (Petroselinum crispum (Mill.) Nyman ex A.W. Hill

Germany
Switzerland

80

Germany

170*

180
60
160
40
Fennel (Foeniculumn vulgare Mill.)
50

180

20
20
20

59

8.8. Leguminosae
CountryN

P2 0 5kg ha- I

FinlandGermany
Netherlands
NorwayUK
USA
Switzerland
FinlandGermany
Netherlands
NorwayUK
USA
SwedenSwitzerland

K2 0

40
80*
50*
75
0
60
15

Pea (Pisum sativum L.)
45
30
50
120
125
150
60
100
25
25
90
90
40
100

40
140*
165"
110
100
70
180
20

Dwarf bean (Phaseolus vulgaris L.)
60
75
60
190
125
150
100
150
150
100
70
70
90
195
30
80

Mg

25
60
0
20

15
60
0

20
Broad bean (Viciafaba L.)
Netherlands
0-50
125
150
60
UK
25
150
100
0
German, Danish and most Dutch N recommendations include the initial
Nmin value: see the source publication for details of sampling depth, etc.
+ see source publication.
Figures in brackets after the German N recommendations are the soil
sampling depth (cm) for Nmin measurements.
As already mentioned, some European countries have adopted the"Nmin" approach to N fertilization, and where this is the case, as indicated byan asterisk, the figures shown include the amount found in the soil atplanting or sowing time.
The figures for Denmark were supplied by J.N. Sorensen of the Danish
Institute of Soil Science. There it is recommended for N to measure soil
Nmin before crop establishment, but they are experimenting withmeasurements made about eight weeks later. Splitting of N applications into
several doses is recommended.

60

The Finnish figures were obtained from the Viljauuspalvelu (soilanalysis service), 00410 Helsinki. N recommendations vary slightly withsoil texture.
The German N recommendations are from Scharpf (1991), who gives
full details of their Nmin system. The P, K and Mg figures apply to class C(medium P, K, Mg analysis) soils in Bavaria (Anon., 1985). They should be
multiplied by 1.5, 1.2, 0.5, or 0 respectively for class A, B, D and E soils(very low.., very high).
The Dutch N figures are taken from Sieling (1992) which should be
consulted for details of the Nmin sampling system recommended in Holland.
The P, K and Mg data are from Anon. (1984), which give adjustments tothese levels for seven categories of P, K and Mg status of the soil.
In Norway there are no official recommendations. The very variable
rainfall means that N and K leaching differs locally: spring Nmin levels are
so low that it is not considered worthwhile to measure them. The figures arefrom Balvoll (1989).
In the UK, the Nmin method is rarely used: all the figures quoted arefrom MAFF (1994), which give the official ADAS recommendations. Those
for N are for index I soils; higher or lower rates apply to index 0 and 2.
Likewise the P, K and Mg figures would vary according to the level of thesenutrients in the soil.
The USA figures are from Lorenz and Maynard (1988) p. 151, and are as
used in the mid-Atlantic states. Values given there for low and high statussoils have been averaged.
Sweden also has no official recommendations; those shown are asprovided by "Hydro Supra" and were kindly passed on by G. Erlandsson of
the Swedish University of Agricultural Sciences. The P 20 5 amounts may be
adjusted ± 25 kg and the K20 amounts reduced by 35 kg according to soil P
and K status. There is some interest among growers in the Nmin system.
The Swiss recommendations are taken from Gysi et al. (1993), p. 77.
The N recommendations apply to soil of "adequate N status", corresponding
to about 120 kg mineral N ha - 1. This can be checked with a quick test. P and
K recommendations are based on exports, and are under review.
The quantities of N, P 20 5, K2 0, and Mg exported from the field withvegetable crops of given yields are shown in Table 9. These amounts do notinclude the non-marketable parts and therefore, are less than the total uptakeof the crop. They should be used to determine the long-term nutrient balance
for a farm.

61

Table 9. Amounts of nutrients removed from the field by vegetable
cropping (from Gysi, 1993) (kg ha-').
If yields differ from these, removal figures should be adjusted
proportionately. Crops marked * are taken from NVRS (1980). Yields shown
are marketable parts: it is assumed that the residues remain in the field.
Crop
Asparagus
Black radish
Broad bean*
Broccoli
Brussels sprouts
Carrots
Cauliflower
Celeriac
Chicory
Chinese cabbage
ChivesCourgette
CucumberDwarf bean
EndiveFennelKohlrabiLamb's lettuce
Leek
Lettuce
Onion
Parsnip*
Peas
RadishRed beet
Red cabbage
Rhubarb
Scorzonera
SpinachSummer cabbage*
Sweet corn
Swede (rutabaga)
Turnip
Winter cabbage

62

Yield, t ha- iN

P2 0 5

K2 0

Mg

6
50

20
85
80
80
130
80
80
85
10
115
170
I 15
20
95
85
80
110
30
110
50
100
146
105
70
150
110
50
55
65
210
95
250
80
180

6
35
30
30
35
40
25
65
3
110
50
25
10
25
40
25
40
10
30
20
50
80
25
25
80
30
30
45
20
48
45
60
35
65

15
195
60
85
90
175
80
135
10
150
155
190
35
75
125
120
160
50
80
70
105
220
35
120
240
145
160
95
120
210
65
175
90
190

1
8

t16
15
18
50
20
35
50
60
30
45
20
25
30
20
35
10
30
25
50
44
10
40
60
45
50
25
16
62
18
60
30
50

-

4
4
9
3
3
1
7
13
9
2
6
3
10
15
1
5
3
6
-

3
3
15
8
7
6
9
-

9
-

It is possible to make certain generalisations about individual crop
species or families. For example:
The alliums (leek, onions, chives, garlic) have thick, sparsely-branchedroots without root hairs: they are concentrated in the top 20 cm of soil:
this is thought to be the reason why, despite having a lower relative
growth rate than most species, they are inefficient at taking up nutrients,
especially P and K (Brewster, 1990). Certainly onions and leeks have
proven to be very responsive to NP starter fertilizer (Plate 8), and thishas reduced the amount of broadcast N required (Stone and Rowse,
1992). Onions are quite susceptible to copper and zinc deficiency, bothof which cause twisting and chlorosis of leaves.
*

Sweet corn requires relatively high temperatures and in Northern Europe
the aim is to accelerate maturity. The work of Peck and MacDonald(1975) at Geneva, New York State, shows that young plants are
responsive to high levels of P and K, and that P hastens maturity. As wehave seen in other examples, response to these high levels of seed-bed P
in such small plants indicates that placement of nutrients near the seed isdesirable. Shrivelled kernels may indicate exhaustion of nitrogen. Sweet
corn is susceptible to zinc deficiency (Lingle and Holmberg, 1957; Table
3) whereas lack of boron can cause barren or partly barren ears.

*

Asparagus is a perennial crop whose shoots (or "spears") are harvested asthey emerge from the soil in the spring. European yields are about 6
tonnes/ha (Gysi et al., 1993) which would imply very low nutrient
removals, but in the high radiation conditions of Arizona, with yields of
12 tonnes/ha, as much as 300 kg N/ha (applied in the irrigation water)
has been found profitable (Gardner and Roth, 1989). Those authors
found a critical N% in the fern of 3.5 in early summer, falling to 2.6 inlate summer. These figures would probably apply elsewhere in theworld.

*

Red beet and spinach belong to the family Chenopodiacae, whose
members are generally salt-tolerant. However, Greenwood et al. (1980a)
showed that, despite belonging to the same family, their potassium
requirements were opposite; spinach having a very large requirement andred beet a very low one. This is in spite of the fact that a red beet crop
contains about three times as much K per hectare as a spinach crop.
Strangely, these differences in responsiveness are not reflected in thenational recommendations in Table 8.4. Their response to P was similar
to that to K, i.e. spinach was extremely responsive and red beet not at all

63

(Greenwood et al., 1980b). Spinach might be expected to respond well toan NPK starter fertilizer, but is usually grown in very close rows which
do not permit the use of the drill unit shown in Plate 7. Excessive use of
N results in a rapid build-up of nitrate in both crops (e.g. Fig. 6): forspinach, this is particularly undesirable when the produce is intended forbaby food. Red beet quite often suffers from boron deficiency, which ismanifested as black cankerous zones in the root tissue.
" Lettuce (family Composilae) is characterized by a high demand forphosphate when very young, and is very responsive to starter solutions
containing N and P. Seedlings are sensitive to salinity, germination being
completely prevented by an osmotic potential of -8 bars as comparedwith -16 bars for cabbage (Page and Cleaver, 1983). Nitrogenrequirement is not large (about 150 kg/ha including Nmin) but plants failto heart if given insufficient N. If more than 50 kg/ha is broadcast as
nitrate for drilled crops, regular watering is advisable until emergence iscomplete. A common nutritional problem with lettuce is tipbum (para
4.4.1. and Plate 5) which occurs unexpectedly and has been estimated tocause $ 2M loss/year in the UK alone (Collier and Tibbits, 1984). Choiceof resistant cultivars, avoidance of soil compaction and excessive soil
cation levels (K, Mg, NH4 ), and early harvesting all help to contain the
problem. Lettuce has also been known to suffer molybdenum deficiency
on acid soil and in slightly acid peat composts.
*

64

Cruciferae, including particularly the Brassica family, have a very highnitrogen requirement but are generally unresponsive to P and K(Greenwood el al., 1980a and 1980b). They have not been responsive to
NP starter solutions in the UK, whether drilled or transplanted. Growers
should look out for signs of magnesium, sulphur, and boron deficiency,
and periodically have leaves analysed for these elements. Brassicas leavelarge residues in the field, which quickly rot down and mineralise inwarm soil. Hence if a second crop per year is taken (e.g. of cauliflowers)
it will require much less fertilizer than the first (Rahn et al., 1992). Thisis a situation where a banded application of N providing a concentration
round the plants equivalent to a broadcast application of 100 kg N/hawould probably be enough to supply them until the residues of theprevious crop have mineralised. If the bands cover 50% of the soil
surface, this would be an average application of 50 kg N/ha.
Cauliflowers are the vegetable crop most sensitive to molybdenum
deficiency, which causes "whiptail" (see Table 3).

Carrots, celery, parsnip, etc., belong to the family Umbelliferae. Carrots,
and to a lesser extent parsnip, require little N: not only is emergence
depressed, but so is the root/shoot ratio, so that abundant top growth may
not signify an equally heavy crop of roots. Carrots are extremely
responsive to P when young, but an experiment at Wellesboume, UK,showed that a two-fold response to P in mid-July had completely
disappeared by late October. Hence an NP starter fertilizer is likely to be
most useful for early carrots.
Members of the family Leguminosae (peas, beans, etc.) are able, by
virtue of the symbiotic bacteria on their roots, to fix atmosphericnitrogen in organic forms. For peas (Pisum sativum) and broad beans(Vicia faba), the bacterium concerned is Rhizobium legurninosarum,
which is common in temperate soils so that these species very rarely
respond to fertilizer N in temperate areas. Dwarf or snap beans, however(Phaseolus vulgaris) and runner beans (Phaseolus coccineus) areassociated with Rhizobium phaseoli, which is less predictable as a sourceof nitrogen. Unless deliberately inoculated, therefore, they should
receive about 150 kg N/ha as fertilizer.
Peas: Fertilizer nitrogen may actually depress the yield of peas anddelays the formation of root nodules. Attempts to restore greenness of
pea crops affected by the pea weevil (Sitona lineatus) or by waterlogging
by applying nitrogen have rarely been successful. Peas are unresponsive
to P but K is very important, and up to 50 kg/ha of K2 0 can safely be
combine-drilled at rows widths up to 20 cm. Amounts in excess of this(e.g. on low-K soils) should be broadcast. Broadcast P and K should be
deeply incorporated into the soil well in advance of drilling.
Dwarf or snap beans: Taylor (personal communication) considers thatthe nitrogen requirement of the crop can be satisfied more reliably by
Rhizobium than by fertilizer provided (a) that the correct strain of
Rhizobium is used (which may be cultivar-specific), and (b) a small
amount of fertilizer N (about 40 kg ha- 1) is broadcast on the seed-bed tocover the period before the roots nodulate. He found that nitrogen
responses were small in UK except on sandy soils.

658.2. Fertigated vegetables in arid and semi-arid zones
8.2. 1. Principles of combined irrigation and fertilization
8.2.1.1. Introduction
Irrigation and fertilization are the most important management factors bywhich farmers control plant development, and fruit yield and quality. The
introduction of trickle irrigation and fertilization (fertigation) (Goldberg etal., 1976; Dasberg and Bresler, 1985) opened up new possibilities forcontrolling water and nutrient supply to crops, and maintaining the desiredconcentration and distribution of ions and water in the soil. The improved
control under drip fertigation compared with sprinkler irrigation andbroadcast fertilization is due to several factors: (a) accurate and uniform
application under all circumstances; (b) application of nutrients to the wettedarea only, where the active roots are concentrated; (c) easy adaptation ofamounts and concentrations of specific nutrients to crop requirements
according to the stage of development and climatic conditions; (d) crop
foliage is kept dry, thus retarding the development of plant pathogens(Yarwood, 1978) and avoiding leaf burn; (e) convenient use of compound,ready-mix and balanced liquid fertilizers with minute concentrations ofminor elements which are otherwise very difficult to apply accurately to thefield.
8.2.1.2. Quantity considerations
To exploit the advantages offered by fertigation systems, two plantrelated quantity factors must be known:
a. Expected dry matter production rate by the plant and the optimal nutrient
concentration in plant tissues which together define the daily nutrient
consumption rate during the growing season that results in maximum yieldand product quality. Such a function [Q(t)] determines the minimal daily
application rate of a given nutrient which is required to maintain a steadystate nutrient concentration in the soil. The actual fertilization rate should
account for the fertilizer use efficiency by the plants (EF<I) and should
therefore be Q/EF. Under good management EF exceeds 0.80 (Shevah andWaldman, 1989).
b. Optimum daily water consumption rate during the season which facilitates
uninhibited photosynthesis by the plants. The transpiration function depends
on meteorological conditions and plant characteristics (Stanhill, 1985;
Hatfield and Fuchs, 1990). The actual irrigation rate exceeds the66transpirational demand as it accounts also for evaporation from the soil
surface and leaching of salts accumulated in the root zone.
8.2.1.3. Intensity considerations
There are two major intensity factors that must be known for proper
fertigation management:a. Target root density distribution in the soil and total root weight.
b. The nutrient concentrations in the soil solution enabling plants to absorb
nutrients according to the prescribed Q(t). Root and nutrient concentrations
have complementary effects, since uptake rate is the integral of the flux xroot surface area (or length) in a given soil sub-volume, over the total
number of sub-volumes in the soil profile. The flux F (mol [cm root] - s- 1) isdetermined by the nutrient concentration in the soil solution at the root
surface, Cr (mol L-1), as shown by the Michaelis-Menten equation:[I]
F = Fma C(Km + Cr)
where Fm (mol [cm root] - s-1) and Km (mol L-') are plant coefficientsobtained in flowing or well stirred nutrient solution experiments.
Representative values of Km and Fmax (eq. [1]) for various crops arepresented in Table 10.
Table 10. Values of Fmax and Km of NO 3, P and K for several plant species
using intact plants in well stirred solution culturea.
NO3

K

5.02

10

3.0

16

1

-

-

-

4

-

-

-

0.88

-

1.0
2.0
6.0

258

-

I
1
19
36

NO 3

K

1.16

0.50

-

6.1
0.10
0.18

(mol cm- 1 s- 1x10 13)

Maize
Soybean
Wheat
Tomatob
Barley

-

5.1
-

Ref.c

Km
P

Fma
P

Crop

-

349

(mol L-1 x10 6)

-

7
-

15

a Subject to the following assumptions: root radius = 0.02 cm; Cmin in
Barber's data disregarded.
b Recalculated.
c Ref.: Barber (1984); Bar-Yosef (1971); Ben Asher et al. (1982); Fried
and Broeshart (1967).
The integration of uptake over the root zone and eq. [1] form the basis
for most models simulating nutrient uptake and plant growth (e.g. Tillitson67

et al., 1980; Marani and Baker, 1981; Jones and Kiniry, 1986, Fishman and
Bar-Yosef, 1995). Such models can be modified into fertigation decision
tools, by comparing the computed uptake rate based on current soil
variables, and the target uptake rate at each time step during the simulation
process. If the computed uptake and the target Q(t) do not match, acorrection (e.g. enhanced or reduced fertigation) must be applied.
8.2.1.4. Importance of flux-concentration relationships
Even without management models, equation [1] can be used to definesome threshold concentrations in the irrigation water. When Cr>Km, theincrease in flux (F) due to an incremental increase in Cr diminishes rapidly,
and hence it is unadvisable to maintain at the root surface a concentration
which sustains a F which exceeds 0. 7 5Fm (namely, Cr= 3 Km). Above thisthreshold concentration any unexpected increase in Cr may cause pollution
and reduced influx of other nutrients (Fried and Broeshart, 1967; Fishman
and Bar-Yosef, 1995).
Another possible application of eq. [1] is to estimate the minimal active
root weight (or length) (Rm) as a function of time, which is required tofacilitate uptake rates according to Q(t):Rm = Q(T)/Frna[2]
The concentration of a non-adsorbing nutrient in the irrigation water(C,) is a first approximation of its concentration in the bulk soil solution(Cb), but not at the root surface. For adsorbing nutrients (P, K), C. should
be corrected for the expected adsorption, based on the partitioning functionof the nutrient between the solution and solid phases in the soil. The
difference between Cr and Cb stems from the rapid depletion of nutrients inthe vicinity of the root, and the slower transport of the nutrients from thebulk soil to the root surface. The difference between C, and Cb diminishes
as fertigation frequency increases. Assuming no mass flow and steady state
concentrations in the soil, the relationship between Cb and Cr is defined by
eq. [3], which was derived from Olsen and Kemper (eq. [61], 1968), and by
eq. [I]:
Cb = Cr [I .+S/(Km + Cr)]
[31
Here, S = Fmaxln(b/a)/(6.28 Dp), b and a are the mean midway distance
between roots and root radius (cm), respectively, and Dp (cm 2 s-1) is the
diffusion coefficient in the soil solution, defined as Dp = K Do exp(ct 0)(Olsen and Kemper, 1968). Here, Do is the diffusion coefficient in water, 0
is the volumetric water content and cc (-10) and K (-0.001 to 0.005) are soil
constants; K decreases as the soil surface area increases. Under regular68fertigation conditions, S may vary between 100 Km and 0.01 Km. For
example, when a = 0.02 cm, b = 2.0 cm, Dp = 1.0 E-8 cm 2 s-1 (a clay soil)and Fma(NO 3) = 5.1 E-13 mol cm- 1 root s-I (tomato, Table 10), S = -30
mM, and is -1 15-fold greater than Km(NO3) of tomato. Under suchconditions, and assuming Cr = K., eq [3] predicts that the Cb/Cr ratio is -50.
Accepting that Cw=Cb, the NO 3 concentration in the irrigation water should
therefore be 50 Km. For thicker (a = 0.04 cm) and denser (b = 0.2 cm) roots,
which grow in a sandy soil (Dp = 2.7 E-6 cm 2 s-1), and for the same F..,S = -50 pM, which is 65-fold smaller than the Km(N0 3) of tomato. In thiscase, the Cb/Cr ratio is -1.1 (eq [3]), and C, is a good estimate of NO 3
concentration at the root surface.
Since mass flow was assumed to be zero in the above approximations, theactual Cb which is required to furnish a certain Cr is less than estimated above.
In several works the parameters in eq [1] were determined in unstirred
solutions, or in growth substrates. Under such circumstances, Km isexpressed as concentration in the bulk soil solution (Kms, Table 11). The
disadvantage of this approach is, that Km, depends not only on the crop
properties, but on soil characteristics and fertigation management also.
Comparison between Kms(N) of tomato plants grown in sand (Table 1) andKm (Table 10) shows that the former is approximately 10-fold greater thanthe latter; Fma(tomato) in the soil is two-fold greater than Fma in wellstirred solution, which is a surprisingly good agreement. The Kms/Km ratioof 10 indicates that Cr in sand is approximately one tenth of Cb, or C,. Thisratio is within the Cb/CT ratios range estimated above.
Table II. Michaelis-Menten constants for N and P of pepper and tomato
plants grown in unstirred solution cultures and in two growth substrates.
Ref

Crop

Nutrient

Fmaa(mol cm- 1 s-1 1013)

Kmsa
(pM)

SystemPepper

N
P
N
P
K

14.0
17.0
11.0
1.8
3.0

550
25
3000
320
1000

Unstirred solution b 2
2
Unstirred solution
13
Sand
15
Rockwool3
AerophonicTomatoa To distinguish from Fmax and Km in well stirred solutions. To transformfrom mol g-' to mol cm- 1, a root radius of 0.02 cm was assumed.
b NH 4 -N:NO 3-N in solution = 1:3; 20- to 30-day-old seedlings.

69

8.2.1.5. Coupling quantity and intensity factors
Under ideal conditions, the quotient Q(t)/(daily irrigation rate) (=C)
should equal the above estimated Cb. The daily irrigation rate (mm/day), is
determined according to estimated reference evapotranspiration multiplied
by a time dependent crop coefficient (Hatfield and Fuchs, 1990). The
irrigation scheduling is determined according to the soil water potential,
usually monitored with tensiometers at reference points in the rhizosphere(Martin et al., 1990). Reference daily evapotranspiration can be estimatedfrom class A pan evaporation or calculated from meteorological data (Hatfieldand Fuchs, 1990). When irrigation quantity is large (e.g. in summer) and theroot system is confined (e.g. high frequency drip irrigation), C may be too
low to furnish the required uptake rate by the plants, as the integral of flux xroot length is too low. In this case, the nutrient application rate should beraised above the target Q(t). This operation is wasteful and environmentally
undesirable. To avoid such problems, plants can be grown with larger rootsystems, such that lower Cr may be sufficient to maintain the target Q(t).
Expanded soil root volumes have a high buffer capacity for water andnutrients, which reduces possible stresses stemming from unexpecteddisrupted supply. However, large root volumes cannot be rapidly enriched ordepleted of nutrients, thus accommodating easy control of uptake according
to time-specific plant needs. Plants with large root volumes usually have lower
water and nutrient use efficiencies than those with confined root systems.

8.2.1.6. Root growth in soils
Factors affecting root growth depend on carbohydrate and other canopysynthesized products, and on physical and chemical conditions prevailing inthe soil root zone. Primary factors affecting root proliferation are (i) soil
resistance to root penetration, (ii) oxygen, P and N concentrations in the soil,and (iii) the presence of elements toxic to root growth. Factor (i) is strongly
dependent on soil water content (0) via the effect of 0 on soil strength, 02
concentration in the soil, and 02 and nutrient transport to roots (Bar-Yosef
and Lambert, 1981). Factors (i) and (ii) explain how fertigation rate andfrequency, which determine 0 and nutrient concentrations and distributionsin the wetted zone (Bresler, 1975), affect root growth and spatial andtemporal distribution in the soil. Characteristic root distributions in soil ofdrip fertigated tomato, pepper, muskmelon and sweet corn, which gave highyields, are presented in Tables 12 and 13. The four root systems werebounded within a soil cylinder 40 cm in radius, which coincided with the70lateral water front position in the soils (data not shown). The depth oftomato and pepper root systems was shallower than sweet corn andmuskmelon, apparently due to differences in root growth characteristics. The
experimental root weight of tomato (Table 12) can be compared with thetheoretical minimum root weight which is necessary to furnish the tomato
1
plant with its maximum Q(N) (eq. [2]). Assuming a Q(N) of 2.5 kg N ha1
1day- (see below), Fm(NO3 ) of (5 mol cm- s-1) E-13 (Table 10) and 8%
1
root dry matter content, a minimum dry root weight of 400 kg ha- is obtained.
The close agreement between the calculated and experimental root weights
indicates that at the time of peak N consumption rate, the roots of drip
fertigated tomato plants must absorb N at a flux which approaches its
maximum capacity. To achieve Fma, the N concentration in the soil solution
at the root surface must be -3 Km.
When calculating the minimal root weight for N uptake by sweet corn
(Q=6 kg N ha-1 day-') (eq. [2]), and using the available Fmax of grain corn
(Table 10), a fresh root weight of 54,000 kg ha-1 is obtained. This root
weight is appreciably higher than the sweet corn fresh root weight which
was found under field conditions (9000 kg ha- 1 , Table 13). The discrepancy
may indicate that sweet corn, which has a much shorter growth season,might have a considerably higher Fmax and lower Km than grain corn.
It is noted that the presented root weight of pepper plants is appreciably
1more than the dry tap root weight of chili pepper (600 kg ha- at acomparable plant age) reported by Beese et al. (1982). However, total dry
matter production in the chili pepper was also considerably lower than in thecurrent case. The presented root weight of tomato plants is similar topreviously published data (Bar-Yosef, 1990).

8.2.2. Managing vegetables fertigation
8.2.2. 1. N, P, K target consumption rates [Q(t)] and supply
Daily nutrient uptake rates that result in optimum yield and product quality[Q(t)] are crop specific and depend on climatic conditions, but are independentof soil characteristics and of irrigation technique. Optimum N, P, K consumption rate vs. time functions for several vegetables grown under normal weather
conditions characteristic of the Middle East region, and the conditions
pertinent to their derivation, are presented in Tables 14, 15 and 16,
respectively.

71

-2

Table 12. Root distribution in a sandy soil and total root weight of drip fertigated pepper and greenhouse tomato plants
which gave optimal yields. Note the different units of root density, presented in their original forma.
Pepperc
Lateral distance (cm)b
Depth (cm)

0-10

11-20

21-30

31-40

0-10

% of total dry root wt in sampled grid

TomatoLateral distance (cm)b
11-20
21-30
31-40
mg dry root/kg dry soil

41-50

0-10

15

12

11

5

320

87

39

9

103

11-20

6

11

7

6

45

72

63

36

103

21-30

5

8

9

4

45

34

43

85

62

31-40

2

1

2

2

28

45

60

75

63

41-50
51-60

-

-

-

22

60

15

28

I

I

I

I

22
I

-

-

--

Total dry roots weightc:

I

1900 kg ha- I

a Sources: Pepper: Bar-Yosef (1991); tomato: Bar-Yosefet aL (1992).
b From the stem towards the edge of the bed, perpendicular to the row.
c Plants stand: pepper 100,000; tomato 23,000 plants/ha.
Sampling times: pepper 120, tomato 90 days after planting.

400 kg ha-1

Table 13. Relative root densitya distribution in the soilb and total fresh root weightC of drip fertigated sweet corn and muskmelon
plants which gave optimal yields.

Depth (cm)
0-10
11-20
21-30
31-40
41-50
51-70
71-90

Sweet corn
Lateral distance (cm)d
21-30
11-20
0-10
Relative root density (%)
48
100
90
67
30
11
10

Total fresh roots weight:

94
84
78
42
50
24
5

47
82
110
52
58
9
6

9000 kg ha-'

31-40
77
104
50
50
36
28
0

Muskmelon
Lateral distance (cm)d
11-20
0-10
Depth (cm)
Relative root density (%)
0- 10
11- 2526- 4041- 6061- 8081-100

100
73
19
92
38
53

54
54
42
35
38
23

21-30
50
46
35
42
23
7

1000 kg ha- I

Relative root density = root density (mg dry root/kg soil) in a given soil cube/root density in a reference soil cube.
The reference root density is: 133 mg dry root/kg soil for sweet corn and 13 mg dry root per kg soil for muskmelon.
b Sweet corn in loess soil; muskmelon in sandy soil.
c Total root weight was estimated by multiplying root density by soil weight represented by the soil cube and summingover the sampled soil volume.
d From the stem towards the edge of the bed, perpendicular to the row.
Source: Bar-Yosef and Sagiv (1985).
t-4

Table 14. Daily nitrogen consumption rate by various vegetable crops grown under drip fertigation as a function of time after
emergence or planting.
Days after
emergenceor planting

Processing
tomatoesGreenhousetomatoesFreshtomatoes

1- 10
11- 20
21- 3031- 4041- 5051- 6061- 7071- 8081- 9091-100101-110111-120

0.10
0.50
1.00
2.80
4.50
6.50
7.50
3.50
5.00
8.00

0.30
0.30
0.30
0.40
0.40
0.45
0.50
1.70
2.80
1.30
2.70
4.60

121-130-131-150
151-180
181-220

-

-

1.00
1.00
1.00
2.00
2.50
2.50
2.50
2.50
1.50
1.50
1.00
1.00
1.50
1.50
4.00
2.00

393

450

-

1

Total (kg N ha- )Bell pepperbakg N ha- I day-1

Eggplant

Potatoes

0.25
0.35
0.40
2.10
2.00
2.10
2.90
2.20
1.40
1.50
0.80
1.00

170

3.90

-

-

2.70

7.00

-

-

-

-

-

-

-

0.05
0.10
0.20
0.25
3.20
2.90
0.25
0.25
0.25
0.25
0.25
1.20
2.40
2.60
2.30
1.90

250

380

205

290

0.10
0.60
2.30
4.00
4.50
5.50
6.00
2.00
1.00
4.00
1.00
-

0.10
0.50
1.50
1.60
1.70
1.60
1.70
2.60
2.80
2.50
2.50
1.50

-

-

Table 14. Continued (Crop and site specific information).

Maor

Black Oval

Desirea

18 Sept' +Selective

26 Aug +14 Jul +Selective

10 Sept +Selective

19 Feb +I Jul

12,00090,000100,000

12,500Freshtomatoes

Variety
Seeding/
planting
Harvesting

VF M82-1-2

675

27 Mar +18 JulF-144(Daniela)
25 Sept"
Selective

Plants ha-1

50,00023,000+ Seeding'SI

PotatoesGreenhousetomatoes

Soil
Marketableyield (t ha-1 )Reference-J.

Eggplant

Processing
tomatoes

Clayey

Sandy

Sandy

160
24

195
14

127
10

++ Planting

Bell pepper
b

a

Sandy
65
47

75
5

Sandy

Sandy

51
6

57
29

-4

Table 14. Daily N consumption rate by various vegetable crops often grown under drip irrigation, as a function of time after
emergence or planting.
Days after
emergenceor planting

Lettuce

CeleryChinesecabbage

Broccoli

I- 10
11- 20
21- 3031- 4041- 5051- 6061- 7071- 8081- 9091-100101-110111-120121-130131-140
141-150
151-160
161-170
Total (kg N ha-1)

0.15
0.45
3.00
3.40
2.20
1.80

0.74
1.11
1.85
2.96
2.24
2.70
1.08
0.84
0.37

-

-

-

0.02
0.07
1.08
1.22
1.75
1.04
3.02
3.41
2.79
2.09
0.93
0.20
0.18
0.15
0.06

0.50
1.00
1.50
3.50
4.50
6.00
4.00
3.00

-

0.17
0.21
0.70
0.88
1.03
0.99
0.99
0.83
0.83
1.00
1.47
1.78
2.00
2.25
-

-

-

-

-

202

-

-

110

150

-

-

0.30
0.07

111

Sweet
corn
kg N ha- I day-I

CarrotMuskmelon

0.15
0.20
0.35
0.90
1.30
2.50
4.30
2.40
1.20
1.00
0.50
0.30

-

0.45
0.87
0.54
0.56
0.93
0.71
1.19
1.09
1.20
1.18
1.54
2.03
2.23
2.34
3.83
3.80
3.47

240

279

151

-

-

-

-

-

Table 14. Continued (Crop and site specific information).

Variety
Seeding/
planting
Harvest date
Plants ha-1
Soil
Marketableyield (t ha-')Reference+ Seeding-4

Lettuce

CeleryChinesecabbage

Broccoli

Sweet
corn

CarrotMuskmelon

Iceberg

FloridaKazomi

WoltamJubilee

Buror

Galia

5 Nov +
25 Jan100,000
Sandy

10 Oct +27 Feb
90,000Loamy

4 Nov +
19 Jan80,000Loamy

30 Aug ++17 Jan33,000Loamy

15 Apr ++5 Jul
75,000Loamy

II Oct +5 Apr
400,000
Loamy

14 JanSelective
25,000
Sandy

45
9

65
27

82
50

13
26

28
49

85
51

56
48

++ Planting

-4

Table 15. Daily P consumption rate by various vegetable crops grown under drip fertigation as a function of time after
emergence or planting.
Days after
emergenceor planting

Processing
tomatoes

1- 10

0.02
0.05
0.16
0.19
0.75
0.80
1.80
0.50
0.50
0.89

11- 20
21- 3031- 4041- 5051- 6061- 7071- 8081- 9091-100101-110111-120121-130131-150
151-180
181-220
Total (kg P ha-')GreenhousetomatoesFreshtomatoes

Eggplant

Bell pepperbakg P ha-I day-I

-

0.10
0.10
0.10
0.20
0.40
0.60
0.30
0.30
0.30
0.10
0.10
0.10
0.20
0.35

0.01
0.02
0.03
0.03
0.03
0.04
0.04
0.18
0.22
0.10
0.30
0.60
0.45
0.17

0.01
0.10
0.25
0.35
0.40
0.20
1.00
0.20
0.50
0.50
0.20
0.10
0.10
0.30

-

050

-

-

-

0.30

-

-

-

0.01
0.01
0.01
0.01
0.02
0.08
0.09
0.05
0.05
0.05
0.09
0.15
0.27
0.31
0.38
0.35

59

65

24

42

31

33

-

0.01
0.10
0.10
0.20
0.25
0.35
0.45
0.35
0.35
0.35
0.25
0.25
0.10
-

Table 15. Daily P consumption rate by various field crops often grown under drip irrigation, as a function of time after
emergence or planting.
Days after
emergenceor planting

Lettuce

CeleryChinesecabbage

Broccoli

I- l0
II- 20
21- 3031- 4041- 5051- 6061- 7071- 80

0.01
0.10
0.50
0.60
0.55
0.45

0.10
0.16
0.31
0.51
0.87
0.81
0.45
0.28

0.00
0.01
0.12
0.13
0.20
0.13
0.36
0.46

81- 90

-

0.28

0.38

91-100101-110

-

0.03
0.04
0.11
0.08
0.20
0.23
0.35
0.29
0.39
0.17
0.18

-

0.32
0.18

0.30
0.54
0.69

-

-

-

-

111-120121-130131-140
141-150
151-160
161-170

Total (kg P ha- )
-.4

22

-

-

36

29

CarrotMuskmelon

0.10
0.15
0.20
0.55
0.85
1.15
0.80
0.20

0.06
0.16
0.12
0.12
0.19
0.20
0.29
0.27

0.03
0.03
0.07
0.18
0.25
0.25
0.35
0.45

-

0.27

0.43

0.24

0.27
0.13

-

0.30

0.09
0.09
0.04
0.01

-

0.07

-

-

0.59
0.58
0.91
1.32
0.88

-

0.81

-

40

73

25

-

-

-

1

Sweet
corn
kg P ha-' day- I

26

-

-

00

Table 16. Daily K consumption rate by various vegetable crops grown under drip fertigation as a function of time after
emergence or planting.
Days after
emergenceor planting

Processing
tomatoesGreenhousetomatoesFreshtomatoes

1- 10
I1- 20
21- 3031- 4041- 5051- 6061- 7071- 8081- 9091-100101-110111-120121-130131-150
151-180
181-220

0.10
0.30
2.00
2.30
8.00
8.50
9.00
4.50
9.20
9.00

0.40
0.50
0.50
0.50
0.55
0.55
0.60
2.20
4.80
2.90
5.70
7.80
7.00
2.00

0.01
1.00
4.00
7.00
7.00
8.00
8.00
3.00
3.00
8.00
6.00
1.00
0.30
0.80

-

-

-

2.00
4.00
3.50
3.50
5.50
5.50
6.00
4.00
6.00
0.10
0.10
1.00
1.00
1.30
3.80
3.00

-

-

520

710

370

580

-

-

Total (kg K ha 1)

Bell pepperab
kg K ha- day -I
0.10
0.90
1.25
1.25
2.50
4.50
5.00
4.50
3.50
5.00
5.50
3.00
-

370

Eggplant

0.00
0.00
0.30
0.80
4.90
7.20
1.30
0.50
0.50
0.50
2.00
3.00
3.00
3.00
1.60
1.60
380

Table 16. Daily K consumption rate by various field crops often grown under drip irrigation, as a function of time after
emergence or planting.
Sweet
corn
kg K ha- day- I

CarrotMuskmelon

1.00
1.50
4.50
5.80
7.20
3.80
6.20
2.00

-

-

-

-

-

-

-

-

-

-

0.40
0.88
0.60
0.60
0.99
0.98
1.62
1.57
1.72
2.14
2.80
5.73
7.00
9.67
11.66
10.19
1.86

0.10
0.25
0.60
1.45
3.00
6.00
7.00
8.00
7.50
3.50
1.00
0.05

-

0.01
0.02
0.74
0.91
1.35
3.04
4.34
3.95
4.09
3.13
2.74
0.96
0.48

219

165

320

604

385

Days after
emergenceor planting

Lettuce

CeleryChinesecabbage

Broccoli

1- 10
II- 20
21- 3031- 4041- 5051- 6061- 7071- 8081- 9091-100101-110111-120121-130131-140
141-150
151-160
161-170

0.20
0.50
5.10
7.80
8.20
3.20.

0.21
0.24
1.33
1.52
2.56
2.78
4.11
4.05
5.56
4.04
5.00
8.60
8.50
10.35

1.70
2.80
4.50
7.20
5.25
5.52
1.37
0.01

-

-

Total (kgK ha-t )

250

224

-

-

-

-

-

-

-

-

-

Considerable differences in uptake rate and in the time at which
maximum consumption rate occurs exist among crops and among varietiesof the same species (e.g. processing, glasshouse, and open-field tomatoes).
In some cases, the consumption function is not monotonic, and exhibits
sharp variation at critical physiological stages. Ignoring temporal variations
in uptake rate may lead to over fertilization, and consequently to salinity
build-up, reduced intake of other nutrients (Fried and Broeshart, 1967) andcontamination of the environment. Sub-optimal supply may result in
depletion of nutrients from the soil and inadequate uptake rate.
Extrapolation of the presented NPK uptake data to environmental
conditions much different from those specified (e.g. different temperaturesor radiation intensities) should be done carefully and treated only as a first
approximation.
8.2.2.2. Nutrient concentrations in irrigation and soil solutions
The suitability of given nutrient concentrations in the irrigation water canbe evaluated if the aforementioned root parameters are known. Let us consider
as an example a fresh tomato (cv. 650) crop grown in a sandy soil and foundat a growth stage of 100 days after planting, at the beginning of January.
According to Table 14, the target N consumption rate (QN) of this cultivar
at this time is 2.7 kg N ha- 1 d- 1. Suppose that the evaporation from class A
pan at that time is 3 mm d- 1 and the crop coefficient is I (= 30 m3 ha-1 d- 1).
Supplying the N through the water yields a concentration (=Cb) of 6.4 mM
N. The question is whether this concentration is appropriate, namely, will it
allow the plants to absorb the amount of N which was added to the soil. To
answer this question we need to estimate N concentration at the root surface(Cr) and compare it with Km. In sandy soils, a C/Gb ratio of 0.1 was shown
to be a sound approximation. If so, C, is expected to be -0.64 mM N, which
is about two-fold greater than Km of tomato (Table 10). Recalling that Crshould preferably be between I and 3 Kin, it can be concluded that theobtained concentration of 6.4 mM N in the irrigation water can safely be used.
A more detailed analysis of the suitability of this concentration would
involve the following steps: (i) calculate FN (eq.[l]) according to Fmax, Km(Table 10) and Cr (= 4.2 10-7 gN cm-1 root d- 1). (ii) Evaluate tomato plantroot weight from data in Table 12, assumed root dry matter content (-5%)
and estimated root radius (0.02 cm) (= 6.4 109 cm root ha-1 ). (iii) Multiply
FN by root length to obtain the rate of N uptake (= 2.7 kg N ha-1 d-1). The
excellent agreement between the calculated uptake and target consumption
rates supports the conclusion obtained above regarding the suitability of 6.4
mM N in the irrigation water. If the crop had a root length which is 70% of82

the above, the agreement between calculated and target uptake rates would
be less impressive, even though 30% difference is still reasonable. If the rootsystem is even smaller and the calculated uptake deviates by more than 30%,
N concentration in the irrigation water should be increased, but should notsurpass 40 Kin, to increase FN. Immediate action should be taken to increase
the plant's root length, as otherwise the excess N application rate over thetarget uptake rate (QN) will cause environmental damage.
If plant parameters are not available, one should take care that Q(t)/(daily
irrigation rate) does not exceed the salinity threshold of the crop of interest,
above which yield and fruit quality decline (Hoffman et al., 1990). An
alternative approach to the direct evaluation of optimal C., is to use
empirical functions relating C, to uptake rate by whole plants. These
functions are specific to soil, crop, plant age and irrigation regime. Two
examples of such functions, for tomato and pepper, are presented in Figs. 7
and 8. According to Fig. 7, C,(NO3) supplied to tomato plants grown in asandy soil and having a root system bounded by a soil cylinder of 30 cm
radius and 60 cm depth should not exceed 100 and 150 mg N L - 1 at the ageof 70 and 140 days after seeding, respectively. These concentrations
correspond to - 2 Kms and - 3 Kms (see Table I1), and to - 2 7 Km and -3 8 K.
(see Table 10), respectively. According to Fig. 8, the optimal Cw(N) of 7696 day old pepper plants grown in two sandy soils is -80 mg L - 1. The
corresponding optimal Cw(K) of the same pepper is 100 mg K L-1 (Fig. 8).
The condition that C. x (daily irrigation rate) = Q(t)/EF must be preserved
also when using the empirical approach.
8-0

A3

Days after seeding 140 - 0

A,

I70-

A
4.0

z

0

-

0

0NO4000

N concentration insoil solution (ppm)Fig. 7. Mean daily nitrogen uptake determined from plant analyses over thetime intervals 60 to 73 and 138 to 165 days after seeding as a function of
average N0 3-N concentration in the solution of a soil cylinder bounded by aradius and depth of 30 and 60 cm, from the trickier, respectively, at specified
times. The curves were fitted by hand (Source: Bar-Yosef and Sagiv, 1982a).
83

I I

I

I

I

I

I

I

I

I

76 -96 days

7

N

0
A

1.04A&
0.407

1.02 A

K<

4
G0

120

180

240

40

80

in0

Ise

4

AA

0

20

Concentration in irrigation solution (mg/L)

Fig. 8. Rates of N and K uptake by pepper plants as a function of theirconcentration in the irrigation water 76 and 96 days after seeding. The
results were obtained at two different sites- Besor and Hazeva, both withsandy soils. Ri is the ratio of seasonal overall irrigation to evaporation froma class A pan (Source: Bar-Yosef et al., 1992).
The required steady state nutrient concentration in the soil that is
expected to be maintained when supply equals optimal uptake rate by theplants, is determined by the pre-seeding basic (usually broadcast)fertilization. To fertilize properly, one must know the relationship between
application rate and nutrient availability to plants on the one hand, andbetween fertilizer dose and nutrient concentration in the soil solution on theother hand. Despite the importance of basic fertilization in creating thebackground nutrient concentrations in the field, it will not be discussed
further in this review.
8.2.2.3. Selecting fertilizers for fertigation
The data in Tables 14, 15 and 16 show the minimal application rates ofN, P and K that must be added to the soil via the water at any growth stage
to satisfy plant demand. The question arises as to what is the recommended
fertilizer to be used for this purpose, and how various conditions in thesystem affect the decision regarding which fertilizer to choose.
84

Fertigation under saline conditions
A 10 meq/L solution has an electrical conductivity (EC) of-I dS/m andan osmotic pressure of approximately 0.30 bar (250C). According to the US
Salinity Laboratory (1954), irrigation water with an EC exceeding 1.44 and2.88 dS/m constitutes a moderate and a high salinization hazard,
respectively. According to Tables 14 and 16, and assuming a daily irrigationof 5 mm (50 m3 ha-l), nitrogen and potassium concentrations in theirrigation water at the time of maximum consumption rate may reach valuesof 15 to 20 meq/L, which correspond to an EC of 1.5-2.0 dS/m. Under suchconditions, and especially where the water EC>I, which is common in aridzones, care should be taken to minimize the amount of accompanying ions
added with the N or K. For example, KCI, which is a cheap source of K,
should be replaced by KNO 3 and K 2HPO 4 , while NH 4NO 3 and urea should
be preferred over (NH4) 2SO 4.
Sodium-based fertilizers (e.g. NaNO 3 or NaH 2 PO 4) are unsuitablesources due to the adverse effect of Na on soil hydraulic conductivity(Bresler el al., 1982) and on plant functioning (Mengel and Kirkby, 1987).
Fertigation solution pH
Different sources of N fertilizers have different effects on irrigation waterand soil pH. High pH values (>7.5) in the irrigation water are undesirable,
because Ca and Mg carbonate and orthophosphate precipitations may occur
in the tubes and drippers. High soil pH may reduce Zn, Fe and P availability
to plants. Consequently, it is not recommended to use ammonia in
fertigation, since it raises the pH when injected into irrigation water.
Compounds which may reduce the irrigation water pH are nitric (NHO 3) andorthophosphoric (H 3PO4) acids. Depending on their price, these sources
may be used to reduce the irrigation water pH down to 5. Lower pH values
are detrimental to root membranes and may increase the Al and Mnconcentrations in the soil solution to toxic levels.
Another factor which affects soil pH, especially at the soil-root interface,is the NH 4-to-NO 3 ratio in the irrigation water. When NH 4 uptake ispredominant, H+ is being excreted from roots. When NO 3 is the major ion
absorbed, OH- is released into the soil (Mengel and Kirkby, 1987). Fluctuations in soil pH around the roots of the order of+ 1.5 pH units due to NH 4 -N
or N0 3-N supply were reported in the literature (Barber, 1984). In tomato
and roses, a stable pH in nutrient solution was maintained when the NH 4 -toNO 3 molar ratio in the solution was between 1:4 and 1:3 (Feigin et al., 1979,1986). Muskmelon which was grown in rockwool with NH 4 as the solesource of N decreased the leachate pH from -7 in the inflowing solution to85

-4 (Bar-Yosef el al., 1995). According to Ganmore-Neumann and Kafkafi(1980, 1983), NH 4 -N is an undesirable source of nitrogen for tomato andstrawberry plants at root-zone temperatures above 30'C, because it isdetrimental to root growth and development.
Nutrient mobility in soils
Spatial distribution of nitrogen in soil is strongly affected by the sourceof N added via the irrigation water. Ammonium is adsorbed by soil colloids
and metal oxides and thus has a restricted mobility relative to theunadsorbed NO3-. Ammonium is nitrified in soil to NO 3 by microbial
mediated reactions, at a rate which depends on soil temperature and moisture
content. The half-life of this process at 25°C and field capacity moisture
content is about 2 weeks (Stanford and Epstein, 1974). In cases of temporary
N application rates in excess of plant consumption, it is advisable to apply
the excess amount as NH 4-N, and thus avoid rapid leaching of theunexploited N outside the root zone.
Urea is a highly soluble, chargeless molecule, which easily moves with
the irrigation water and is distributed in the soil similarly to NO3-. At 25°C,
it is hydrolyzed by soil microbial enzymes into NH 4 within a few days. Thishydrolysis results in an increase in soil pH, which in soils of pH>7.5 may
reduce P availability to plants.
Phosphorus mobility in soil is very restricted due to its strong retention
by soil oxides and clay minerals. Continuous application of orthophosphatethrough the irrigation water was shown to be superior to applying P at
adequate quantities as basic fertilization (Bar-Yosef et al., 1989). This
stemmed from the fact that both P adsorption and P crystallization, which
reduce P concentration in the soil solution and thus decrease P uptake rateby plants and P migration distance in the soil, are time-dependent reactions.
The half-life of these reactions is roughly a few hours and several weeks,
respectively. Due to the frequent P application via the water, the residence
time of P in the soil was reduced appreciably, and P concentration in the soil
solution between successive fertigations was considerably higher than
expected from adsorption and precipitation equilibrium considerations.
When choosing the P fertilizer for fertigation, care must be taken to
avoid P-Ca and P-Mg precipitation in the tubes and emitters (Bar-Yosef andImas, 1995). From this standpoint, acid P fertilizers (e.g. phosphoric acid or
monoammonium phosphate) are recommended, because the monovalent(H 2 PO4-)-Ca and Mg salts are far more soluble than the HP0 42 - Ca and Mg
salts.

86

Ready-mix fertilizers
Commercial ready-mix fertilizers (in solid or liquid form) arecharacterized by their nutrient contents, elements weight ratio, and specificchemicals constituting the fertilizer. The combined data in Tables 5, 6 and 7
may help to define the N, P, K weight ratio of a given compound fertilizer
designed to supply these elements to a given crop during a certain growth
period. The compounds constituting a ready-mix fertilizer (source of N andaccompanying ions) should be evaluated based on the principles discussed
in preceding sections.
8.2.3. Monitoring the plant-soil system
The principles outlined in section 2 allow one to fertilize during thegrowing season in order to sustain optimum crop growth and yield. The
optimal consumption rates by plants as shown in Tables 5, 6 and 7 are theproduct of optimal dry matter production (ODM) times optimum nutrient
concentration in plant tissues (ONC). Both functions are available but notpresented in this review. By monitoring plant dry weight and nutrient
concentrations therein, and comparing the data with the ODM and ONC atcritical growth stages, one can determine whether the crop is developing andabsorbing nutrients according to the required rates. Any deviation from the
ODM and ONP values must be followed by correction of the nutrient andwater supply rates, so that conditions in the soil will conform with therequired concentrations.
The required nutrient concentrations in the soil solution which facilitate
optimal consumption rate by plants can be estimated according to thepreceeding guidelines. By means of soil tests, the deviation between
prevailing and optimum concentrations can be determined, and correction
measures to restore the required concentrations in the soil can be undertaken.
The soil water content (0) must be maintained at a level that will not
limit water and nutrient movement to the roots. Discussion of the principles
of irrigation management (rates and timing), showing how to determine therequired 0, or matric potential (o) in a given soil, and how to obtain andmaintain it there, are outside the scope of this work. For supplementary
information on this subject, the reader is refered to reviews by Bucks et al.
(1982) and Dasberg and Bresler (1985). To ensure that water will not
become an uptake-limiting factor on the one hand, and will not cause
anaerobic conditions due to over-irrigation on the other hand, soil 0, or o,must be monitored periodically. Soil matric potential is being monitored
under field conditions by tensiometers, and 0 by neutrone probes (Gardner,87

1986) or TDR (time domain reflectometry, Topp and Davis, 1985). Under
trickle irrigation, the recommended e should be between -8 and -15 char insandy soils and between -10 and -30 char in clay soils.
Where possible, nutrient concentrations in the soil solution should also
be monitored in order to ensure that they are within the required concentration range. This can be done by either of two approaches. The first approach
involves soil sampling at one or more reference positions in the root zone asa function of time, and extraction to determine soluble and sorbed nutrient
concentrations in the soil. The second approach is to sample the soil solution
directly by means of vacuum cups inserted permanently in the soil, andanalyze the collected solution for various nutrient concentrations in it. The
convenient operation and low price of the vacuum cup system have made itvery popular with farmers. The most commonly used vacuum cup isconstructed of porous ceramics and is described in detail by Rhoades andOster (1986).
None of the above mentioned methods gives the true nutrient concentration in the soil or soil solution. However, the results obtained are closely
correlated with the real concentrations, and hence can show variations in
nutrient status in soil (depletion or accumulation trends) over time.
8.2.4. Concluding remarks
There have been significant advances in trickle irrigation and fertilizationequipment, automation and maintenance devices within the past decade.
Efficient utilization of this equipment is hampered by gaps in our knowledge
regarding optimum consumption rate of various nutrients by crops as afunction of time, concentration-flux of uptake relationships, and lack of
accurate, reliable and rapid monitoring devices in the soil-plant system. In
this work, the available biological data pertinent to vegetable fertigation
during the season have been presented. Guidelines for rational use ofdifferent fertilizers through the water have been proposed, and ways toestimate required nutrient concentrations in the soil solution to obtainpredefined optimal uptake rates have been discussed. The biological database presented in this work is still very limited, and cannot be simply
extrapolated to different climatic conditions. It should be regarded, however,as an example of the type of information needed to gain full benefit fromsophisticated fertigation systems.
Drip fertigation strongly affects plant root volumes. More research isneeded to clarify soil physical and chemical effects on root growth, uptake
and excretion. An enhanced understanding of these phenomena will help us
in using drip fertigation to produce desired root systems, and thus obtain88

plants more efficient in utilizing nutrients and water from the soil. It will
also help to design drip fertigation systems based on root characteristics, aswell as soil hydraulic properties, as planning parameters.
Monitoring should be advanced on two fronts: (i) Development of
reliable standard curves defining the optimal dry matter production rate,
nutrient concentrations, and water status in plants as a function of time, overa wide range of growth conditions. Nutrient status, or related parameters(e.g. nitrate in petioles) should be determined by the growers themselves toachieve a short response time in correcting observed deviations between
current and standard curve results. (ii) Improving the methodology ofdetermining water status in soil and nutrient concentrations in the soil
solution. These monitoring tests should also be done by the farmers in thefield, so that correction measures based on the obtained results will beeffective.

Acknowledgements (Chapters I to 8.1)
I would like to thank Chris Dawson, Wolfgang Maibaum, Geoffrey Gent,
Hans-Christoph Scharpf, Christian Gysi, Lea Hiltunen, Sal Locascio, Mal
Westcott, Joni Sorensen, Gudmund Balvoll, John Taylor, Duncan
Greenwood, David Stone and many other colleagues for their invaluable
help in the preparation of this book.

References (Chapters I to 8.1)
Alt, D. (1984): Langjtthriger Feldversuch zur P, K-, und Mg-Dtingung vonGembisekulturen. Gartenbauwissenschaft 49, 270-279.
Anon. (1985): Arbeitskalender for das Freiland. Gemflse 6/1985, 288-293.
Anon. (1984): Bemestingsadviesbasis intensieve vollegrondsgroenteteelt.
Consulentschap voor bodem- water- en bemestingszaken in deakkerbouw en tuinbouw, Wageningen, The Netherlands.
Archer, J. (1988): Crop nutrition and fertilizer use. Farming Press, Ipswich,UK.
AVRDC (1985): Effect of time, form, and concentration of nitrogen
application on Chinese cabbage tipburn. Progress Report, Asian
Vegetable Research and Development Center, 385-393. Tainan, Taiwan.
Balvoll, G. (1989): Gronsakdyrking p5 friland. 4th ed. Landbruksforlaget,
Oslo.
Barber, S.A. (1962): A diffusion and mass flow concept of soil nutrient
availability. Soil Science 93, 39-49.
89

Barker, A.V. and Mills, H.A. (1980): Ammonium and nitrate nutrition ofhorticultural crops. Hortic. Reviews 2, 395-423.
Barker, A.V. (1989): Genotypic responses of vegetable crops to nitrogen
nutrition. Hort. Science 24, 584-591.
Barley, K.P. (1970): The configuration of the root system in relation to
nutrient uptake. Advances in Agronomy 22, 159-201.
Batra, B.R. and Kalloo (1990): Effect of different levels of irrigation andfertilization on growth and yield of carrot (Daucus carota L.) for root
production. Vegetable Science 17, 127-139.
BDH (1984): The snappy sap test - its use with vegetable crops. BDH Ltd.,
Poole, UK.
Berard, L.S. (1990): Effects of nitrogen fertilization on stored cabbage. 1:
Development of physiological disorders on tolerant and susceptible
cultivars. J. Hort. Sci. 65, 289-296.
Bergmann, W. and Neubert, P. (1983): Pflanzendiagnose und Pflanzenanalyse. Fischer Verlag, Jena, DDR.
Beringer, H. and Trolldenier, G. (1978): Influence of K nutrition on the
response to environmental stress. In: Potassium research - Review andtrends. International Potash Institute, Bern.
Bierhuizen, J.F., Ebbens, J.L. and Kooman, N.C.A. (1973): Effects oftemperature and radiation on lettuce growing. Netherlands Journal of
Agricultural Science 21, 110-116.
Bshmer, M. (1980): Der Mineralstickstoffgehalt von Bdden mit Feldgemilsebau und seine Bedeutung fur die Stickstoffemahrung der Pflanze.
Doctoral Thesis, Horticulture Faculty, Univ. Hanover, FRG.
Bould, C. (1983): Methods of diagnosing nutrient disorders in plants. In:
Diagnosis of mineral disorders in plants. Vol. 1: Principles. H.M.S.O.,
London.
Brewster, J.L. (1990): In: Onions and allied crops. Vol. 1, Botany,
Physiology, and Genetics. Eds. H.D. Rabinowitch and J.L. Brewster.
CRC Press, Boca Raton, Florida, USA.
Brown, J.C. (1978): Mechanism of iron uptake by plants. Plant, Cell andEnvironment 1,249-257.
Bunt, A.C. (1976): Modem potting composts. George Allen and Unwin,
London.
Burghardt, H. and Ellering, K. (1986): Vertrtglichkeit und Wirkung vonBlattdingungsmassnahmen bei Gemtlsekulturen. Gartenbauwissenschaft
51, 58-62.
Burns, I.G. (1974): A model for predicting the redistribution of salts applied
to fallow soils after excess rainfall or evaporation. J. Soil Science 25,
165-178.
90

Burns, I.G. (1990): The effects of continuity of early nitrogen nutrition on
growth and development of Lactuca saliva. In: Plant nutrition physiology and applications; Ed. M.L. van Beusichem. Kluwer
Academic Publishers, The Netherlands.
Bussler, W. (1958): Manganvergiftung bei h6heren Pflanzen. Z. Pflanzenernlihrung Dingung 81, 256-265.
Carolus, R.L. (1936): Experiences with rapid chemical tests for thedetermination of nutrient deficiencies in vegetable crops. Proc. Amer.
Soc. Hort. Sci. 33, 579-83.
Chapman, H.D. (1966): Diagnostic criteria for plants and soils. Univ.
California Div. of Agric. Sciences.
Claasen, N. (1992): Nutrient acquisition and soil-plant interactions. Proc.
2nd ESA Congress, Warwick Univ. (Ed. A. Scaife), 218-227.
Clarkson, D.T. and Hanson, J.B. (1980): The mineral nutrition of higher
plants. Annual Review of Plant Physiology 3 1, 239-298.
Clement, C.R., Hopper, M.J. and Jones, L.H.P. (1978): The uptake of nitrateby Lolium perenne from flowing nutrient solution. Journal of
Experimental Botany 29, 453-464.
Collier, G.F. and Tibbits, T.W. (1982): Tipbum of lettuce. Horticultural
Reviews 4, 49-65.
Cooke, G.W., Jackson, M.V., Widdowson, F.V. and Wilcox, J.C. (1956):
Fertilizer placement for horticultural crops. Journal of Agricultural
Science, Cambridge 47, 249-256.
Costigan, P.A. (1985): A survey of nutrient concentrations and early shootand root growth of drilled lettuce in twenty-one commercial sowings in
one year. J. Hort. Sci. 60, 233-243.
Costigan, P.A. (1988): The placement of starter fertilizer to improve theearly growth of drilled and transplanted vegetables. Proc. Fertilizer
Society No. 274, 24 pp. The Fertilizer Society, London.
Cummings, G.A. and Wilcox, G.E. (1968): Effect of potassium on quality
factors - fruits and vegetables. In: The role of potassium in agriculture.
American Society of Agronomy, Madison, Wisconsin, USA, 243-267.
Espinoza, L., Sanchez, C.A. and Schueneman (1993): Celery yield responds
to phosphorus rate but not phosphorus placement on histosols. Hort. Sci.
28, 1168-1170.
Everaats, A.P. (1993): Strategies to improve the efficiency of nitrogen
fertilizer use in the cultivation of brassica vegetables. Acta Hort. 339,
149-160.
Farrer, K., Caldwell, T.H. and Archer, F. (1976): Trace element deficiencies
in crops. ADAS Advisory paper No. 17. MAFF, Pinner, UK.

91

Fenn, L.B. and Miyamoto, S. (1981): Ammonia loss and associatedreactions of urea in calcareous soils. Soil Sci. Soc. Am. J. 45, 537-540.
Fenwick, G.R., Griffiths, N.M. and Heaney, R.K. (1983): Bitterness inBrussels sprouts (Brassica oleracea L. var. Gemmifera). The role ofglucosinolates and their breakdown products. J. Sci. Food and Agric. 34,
73-80.
Fink, N. and Scharpf, H.C. (1993): N-Expert - A decision support system forvegetable fertilization in the field. Acta Hort. 339, 67-74.
Fischer, J. (1992): The influence of different nitrogen and potassium
fertilizers on the chemical flavour composition of kohlrabi (Brassica
oleracea var. gongylodes L.). J. Sci. Food. and Agric. 60, 465-470.
F6hse, D., Claasen, N. and Jungk, A. (1988): Phosphorus efficiency ofplants. 1, External and internal P requirement and P uptake efficiency ofdifferent plant species. Plant and Soil 110, 101-109.
Fthse, D., Claasen, N. and Jungk, A. (1991): Phosphorus efficiency ofplants. II. Significance of root radius, root hairs and cation-anion balance
for phosphorus influx in seven plant species. Plant and Soil 132, 261262.
Follett, R.H., Murphy, L.S. and Donahue, R.L. (1981): Fertilizers and soil
amendments. Prentice-Hall, New Jersey, USA.
Forman, D., AI-Dabbagh, S. and Doll, R. (1985): Nitrates, nitrites andgastric cancer in Great Britain. Nature 313, 620-625.
Freeman, G.G. and Mossadeghi, N. (1970): Effect of sulphate nutrition on
flavour components of onion (Allium cepa). J. Sci. Food and Agric. 21,
610-615.
Freeman, G.G. and Mossadeghi, N. (1972): Influence of sulphate nutritionon flavour components of three cruciferous plants: radish (Raphanus
sativus), cabbage (Brassica oleracea capitata) and white mustard(sinapis alba). J. Sci. Food and Agric. 23, 387-402.
Gardner, B.R. and Roth, R.L. (1989): Plant analysis for nitrogen fertilizationof asparagus. J. Am. Soc. Hort. Sci. 114, 741-745.
Geraldson, C.M. (1954): The control of blackheart in celery. Proc. Am. Soc.
Hort. Sci. 63, 353-358.
Gooding, M.J. and Davies, W.P. (1992): Foliar urea fertilization of cereals: a
review. Fert. Res. 32, 209-222.
Graham, R.D. and Webb, M.J. (1991): Micronutrients and disease resistanceand tolerance in plants. In: Micronutrients in agriculture. 2nd Ed. Soil
Sci. Soc. Am., Madison, Wisconsin, USA, 329-370.
Greenwood, D.J., Cleaver, T.J. and Turner, M.T. (1974a): Fertilizer
requirements of vegetable crops. Proc. Fert. Soc. No. 145. The Fertilizer
Society, London.
92

Greenwood, D.J., Wood, J.T. and Cleaver, T.J. (1974b): A dynamic modelfor the effects of soil and weather conditions on nitrogen response. J.
Agric. Sci., Cambridge 82, 455-467.
Greenwood, D.J., Cleaver, T.J., Loquens, S.M.H. and Niendorf, K.B.
(1977): Relationship between plant weight and growing period forvegetable crops grown in the United Kingdom. Ann. Bot. 41, 987-997.
Greenwood, D.J., Barnes, A. and Cleaver, T.J. (1978): Measurement andprediction of the changes in protein contents of field crops during
growth. J. Agric. Sci., Cambridge 91,467-477.
Greenwood, D.J., Cleaver, T.J., Turner, M.K., Hunt, J., Niendorf, K.B. and
Loquens, S.M.J. (1980a): Comparison of the effects of potassium
fertilizer on the yield, potassium content and quality of 22 different
vegetable and agricultural crops. J. Agric. Sci., Cambridge 95, 441-456.
Greenwood, D.J. el al. (1980b): ibid. 95, 457-469.
Greenwood, D.J., Kubo, K., Burns, I.G. and Draycott, A. (1989): Apparent
recovery of fertilizer N by vegetable crops. Soil Sci. & Plant Nutr. 35,
367-381.
Gysi, Ch. (1993): Nfihrstoffbilanz im Gesamtbetrieb. Flugschrift Nr. 127.
Eidg. Forschungsanstalt for Obst-, Wein- und Gartenbau, Widenswil,
Switzerland.
Gysi, Ch., Ryser, J.P., Matthaus, D. and Koch, W. (1993): In: Richtlinien fojr
den Schweizerischen Gemflsebau. Schweiz. Gemilse-Union, Ins,
Switzerland.
Hahn, E. (1985): Bormangel bei Gemase. Nachrichtenblatt ftir den
Pflanzenschutz in der DDR, 39, 206-209.
Hansen, S., Jensen, H.E., Nielsen, N.E. and Svendsen, H. (1993): The soil
plant system model DAISY. Jordbrugsforlaget, Copenhagen.
Haynes, R.J. (1984): Lime and phosphate in the soil-plant system. Adv.
Agron. 37, 249-315.
He Tianxu, He Chengdu and Hirdter, R. (1994): The effects of K and Mg
fertilizers applied to cabbage on yield, quality and economic returns.
Potash Review No. 2, 1994, 1-5.
Hewitt, E.J. (1983): The effects of mineral deficiencies and excesses on
growth and composition. In: Diagnosis of mineral disorders in plants.
Vol. 1: Principles. H.M.S.O., London.
Hinton, L. (1991): The European market for fruit and vegetables. Elsevier,
London.
Hole, C.C. and Scaife, A. (1993): An analysis of the growth response ofcarrot seedlings to deficiency in some mineral nutrients. Plant and Soil
150, 147-156.

93

Huber, D.M. and Watson, R.D. (1974): Nitrogen form and plant disease.
Annual review of Phytopathology 12, 139-165.
Ikeda, H. (1988): Studies on the utilization of nitrogen by vegetable crops
with special reference to the form of nitrogen supplied. Bull. Univ.
Osaka Prefecture 40, 69-117.
IPI (1976): Fertilizer use and plant health. International Potash Inst., Bern.
Jenkinson, D.S., Fox, R.H. and Rayner, J.H. (1985): Interactions between
fertilizer nitrogen and soil nitrogen - the so-called "priming" effect. J.
Soil Sci. 36, 425-444.
Jones, F.G.W. (1976): see IPI (1976), p. 2 3 3 .
Keipert, K., Wedler, A. and Overbeck, G. (1990): Alternative cultivation ofapples and vegetables. Schrifienreihe der Landwirtschaftskammer
Rheinland No. 66.
Khasawneh, F.E. and Doll, E.C. (1978): The use of phosphate rock for direct
application to soils. Adv. Agr. 30, 159-206.
Kirtly, Z. (1976): see IPI (1976), p. 33.
Kolota, E. (1984): Effect of fertilization methods and nitrogen form on
Vegetable yields with and without irrigation. Biuletyn Warzynwniczy 27.
Whitehead cabbage 203-235; Beet roots 237-260; Leeks 261-282.
Kramer, P. (1949): Plant and soil water relationships. McGraw-Hill, NewYork.
Krikun, J., Haas, J.H., Dodd, J. and Kinsbursky, R. (1990): Myccorhizal
dependence of four crops in a P-absorbing soil. Plant and Soil 122, 213217.
Lagatu, H. and Maume, L. (1924): Etude, par I'analyse pdriodique desfeuilles, de linfluence des engrais de chaux, de magntsie, et de potasse
sur [a vigne. Comptes rendus de I'Acad~mie des Sciences 179, 932-934.
Leuchs, F. (1959): Uber Beziehungen zwischen Fiulniserscheinungen,
Wundheilung und Kaliversorgung an Rosenkohl. Zeitschrift fur
Pflanzenkrankheiten und Pflanzenschutz 66, 499-508.
Lindsay, W.L. (1972): Zinc in soils and plant nutrition. Advances inAgronomy 24, 147-186.
Lingle, J.C. and Holmberg, D.M. (1957): The response of sweet corn tofoliar and soil zinc on a zinc deficient soil. Proc. Am. Soc. Hort. Sci. 70,
308-315.
Locascio, S.J. (1987): Progress in nutrition of Florida vegetables during thepast 100 years. Proc. Fla. State Hort. Soc. 100, 398-405.
Locascio, S.J. and Fiskell, J.G.A. (1987): Vegetables needs for
micronutrients in perspective. Soil and Crop Sci. Soc. of Florida Proc.
47, 12-18.

94

Lorenz, O.A. and Maynard, D.N. (1988): Knott's Handbook for Vegetable
Growers. 3rd Ed. John Wiley & Sons, New York.
Lorenz, O.A., Weir, B.L. and Bishop, J.C. (1972): Effect of controlledrelease nitrogen fertilizers on yield and nitrogen absorption by potatoes,
cantaloupes, and tomatoes. J. Am. Soc. Hort. Sci. 97, 334-337.
Lorenz, H.P., Schlaghecken, J. and Engl, G. (1989): Gezielte StickstoffVersorgung im GemOsebau nach dem "Kulturbegleitenden Nmin
Sollwerte (KNS)-System". Neustadter Hefte No. 26. LLFLWG, Neustadt
an der Weinstral3e, FRG.
Lucas, R.E. (1968): Potassium nutrition of vegetable crops. In: The role ofpotassium in agriculture. American Society of Agronomy, Madison,
Wisconsin, USA, 489-498.
MacNicol, R.D. and Beckett, P.H.T. (1985): Critical tissue concentrations ofpotentially toxic elements. Plant and Soil 85, 107-129.
MAFF (1994): Fertilizer recommendations for agricultural and horticultural
crops (RB209). 6th Ed. MAFF, London.
Marschner, H. (1986): Mineral nutrition in higher plants. Academic Press,
London.
Mattusch, P. (1978): Ein Beitrag zur Verminderung der durch den
Kohlhemieerreger Plasmodiophora brassicae verursachten Schaden
durch den Einsatz von Kalkstickstoff. Nachrichtenblatt Deutscher
Pflanzenschutzdienst (Braunschweig) 30, S, 150-152.
Mayer, C., Venter, F. and Dehne, H.W. (1989): Zur Bedeutung dervesikular-arbuskularen Mykorrhiza ftr die Kultur von Gemusejungpflanzen. Bodenkultur 40, 37-45.
Maynard, D.N. (undated): Calcium deficiency disorders in vegetable crops.
h: A guide to the uses of calcium nitrate for crop production. Wilson &Geo. Meyer, San Francisco.
Maynard, D.N., Barker, A.V., Minotti, P.L. and Peck, N.H. (1976): Nitrateaccumulation in vegetables. Adv. Agron. 28, 71-118.
Maynard, D.N. and Barker, A.V. (1972): Internal browning of Brussels
sprouts: a calcium deficiency disorder. J. Am. Soc. Hort. Sci. 97, 789792.
Maynard, D.N. and Locascio, S.J. (1982): Nutrition of vegetable crops in
Florida, USA. Proc. 21st International Horticultural Congress, Hamburg,
FRG, Vol. 2, 710-725.
Maynard, D.N. and Lorenz, O.A. (1979): Controlled-release fertilizers forhorticultural crops. Hort. Review 1,79-140.
Mengel, K. and Kirkby, E.A. (1987): Principles of plant nutrition.
International Potash Institute, Bern.

95

Miller, E.V., Army, T.J. and Krackenberger, H.T. (1956): Ascorbic acid,carotene, riboflavin and thiamine contents of turnip greens in relation tonitrogen fertilization. Soil Sci. Soc. Am. Proc. 20, 379-382.
Milthorpe, F.L. and Moorby, J. (1974): An introduction to crop physiology.
Cambridge University Press, Cambridge, UK.
Mitscherlich, E.A. (1909): Das Gesetz des Minimums und das Gesetz desabnehmenden Bodenertrages. Landwirtschaftliches Jahrbuch 38, 537-52.
Mitscherlich, E.A. (1928): Die zweite Annfiherung des Gesetzes der Effekteder Wachstumsfaktoren. Zeitschrift fdr Pflanzenemahrung A12, 273.
Neeteson, J.J. (1985): Effectiveness of the assessment of nitrogen fertilizer
requirement for potatoes on the basis of soil mineral nitrogen. In:
Assessment of nitrogen fertilizer requirement. Eds: Neeteson, J.J. andDilz, K. Inst. for Soil Fertility, Haren, The Netherlands.
Nitsch, A. (1984): Mit Teststabchen und Reflektometer. Hannoversche
Land- und Forstwirtschaftliche Zeitung 39.
Nitsch, A. and Varis, E. (1991): Nitrate estimates using the Nitrachek testfor precise N-fertilization during plant growth and, after harvest, forquality testing potato tubers. Potato Research 34, 95-105.
NVRS (1980): The NPK Predictor. National Vegetable Research Station,
Wellesboume, CV35 9EF, UK.
Olsen, C. (1950): The significance of concentration for the rate of ion
absorption by higher plants in water culture. Physiologia Plantarum 3,
152-164.
Page, E.R. (1972): Ammonia as a fertilizer for vegetables. Reports on the
Progress of Applied Chemistry 56, 448-455.
Page, E.R., Tatham, P.B. and Wood, M.B. (1974): Aqueous ammonia as anitrogen fertilizer for single harvested Brussels sprouts. Exp. Hort. 26,
82-90.
Page, E.R. and Cleaver, T.J. (1983): Effects of nitrogen fertilizers on theemergence of vegetable seedlings. J. Sci. Food and Agric. 34, 13-22.
Peck, N.H., Cantliffe, D.J., Shallenberger, R.S. and Bourke, J.B. (1974):
Table Beet (Beta vulgarisL.) and nitrogen. Search Agric. 4, 1-25.
Peck, N.H. and MacDonald, G.E. (1975): Plant response to concentrated
superphosphate and potassium chloride salts. VI. Sweet Corn (Zea mays
L. var. rugosa). Search Agric. 5, 1-35.
Peck, N.H. and Stainer, J.R. (1970): Plant response to concentrated superphosphate and potassium chloride fertilizers: Ill. Cabbage (Brassica
oleracea). New York Agric. Exp. Stn. Bull. 830.
Penman, H.L. (1948): Natural evaporation from open water, bare soil, andgrass. Proceedings of the Royal Society, London; Series A, 193, 120.

96Perrenoud, S. (1990): Potassium and plant health. 2nd Ed. International
Potash Institute, Bern.
Plant, W. (1956): The effects of molybdenum deficiency and mineral
toxicities on crops on acid soil. J. Hort. Sci. 31, 163-176.
Prasad, R., Rajale, G.B. and Lakhdive, B.A. (1971): Nitrification retarders
and slow-release nitrogen fertilizers. Adv. Agron. 23, 337-383.
Purvis, E.R. and Carolus, R.L. (1964): Nutrient deficiencies in vegetable
crops. In: Hunger signs in crops. 3rd Ed. (H.B. Sprague, Ed.). David
McKay, New York.
Rahn, C.R., Vaidyanathan, L.V. and Paterson, C.D. (1992): Improving theprediction of nitrogen for brassica crops. Proc. 2nd ESA Congress,
Warwick Univ. (Ed. A. Scaife), 424-425.
Randall, G.W. and Hoeft, R.G. (1988): Placement methods for improved
efficiency of P and K fertilizers: a review. J. Prod. Agric. 1, 70-79.
Rao, J.K., Sahrawat, K.L. and Burford, J.R. (1987): Diagnosis of irondeficiency in groundnut, Arachis hypogea L. Plant and Soil 97, 353-359.
Reuter, D.J. and Robinson, J.B. (1986): Plant analysis: An interpretation
manual. Inkata Press, Melbourne.
Roll-Hansen, J. (1974): Fertilizer experiments with carrots on peat soil.
Forskning Og Forsoki Landbruket 25, 201-218.
Sanchez, C.A., Burdine, H.W., Guzman, V.L. and Beverly, R.B. (1989):
Management of high pH histosols for lettuce production. Proc. Florida
State Hort. Soc. 102, 341-343.
Scaife, M.A. (1968): Maize experiments in Western Tanzania. J. Agric. Sci.,
Cambridge 70, 209-222.
Scaife, M.A. (1974): Computer simulation of nitrogen uptake and growth.
Plant Analysis and Fertilizer Problems. Proc. 7th Intern. Coll., Hanover,
FRG, 413-425.
Scaife, A. and Turner, M.K. (1983): Diagnosis of mineral disorders invegetables. Vol. 2. Vegetables. H.M.S.O., London.
Scaife, A. and Turner, M.K. (1985): Effect of nitrogen top-dressing on
Brussels sprout flavour. Tests of Agrochemicals and Cultivars 106, 172173.
Scaife, A. and WuZT, D.C.E. (1990): Effects of nitrogen and irrigation on
hollow stem of cauliflower (Brassica oleracea var. Botrytis). J. Hort. Sci.
65, 25-29.
Scaife, M.A. and Barnes, A. (1977): The relationship between crop yieldand petiole nitrate concentration at various growth stages. Plant and Soil46, 705-712.
Scaife, M.A. and Bray, B.G. (1977): Quick sap tests for improved control ofcrop nutrient status. ADAS Quarterly Review 27, 137-145.
97

Scaife, A., Saraiva Ferreira, M.E. and Turner, M.K. (1986): Effect ofnitrogen form on the growth and nitrate concentration of lettuce. Plant
and Soil 94, 3-16.
Scaife, A. and Turner, M.K. (1987): Field measurements of sap and soil
nitrate to predict nitrogen top-dressing requirements of Brussels sprouts.
J. Plant Nutr. 10, 1705-1712.
Scaife, A. and Turner, M.K. (1984): Use of Merckoquant nitrate test strips
for optimization of vegetable nitrogen hutrition. Proc. 6th Intern. Coll.
for the optimization of plant nutrition, Montpellier, France. Vol. 2, 617624.
Scharpf, H.C. (1991): StickstoffdtIngung im Gemtisebau. AID, Bonn, FRG.
Scharpf, H.C. and Weier, U. (1988): Abgestimmte Sollwerte for
Stickstoffdtingung im Gemfisebau. In: "Die industrielle Obst- undGemuseverwertung", No. 4/1988.
Schrage, R. (1990):
Methoden zur Bestimmung des StickstoffDtingerbedarfs von Gemusekulturen mit geringem analytischen
Aufwand. Doctoral Thesis, Hort. Fac., Univ. Hanover.
Shallenberger, R.H. and Moyer, J.C. (1958): Relationships between
pyrrolidonecarboxylic acid and an off-flavor in beet puree. Agric. Fd.
Chem. 6, 604-606.
Sharpley, A.N. and Menzel, R.G. (1987): The impact of soil and fertilizer
phosphorus on the environment. Adv. Agron. 41, 297-324.
Shorrocks, V.M. and Alloway, B.J. (undated): Copper in plant, animal, andhuman nutrition. Copper Dev. Assoc., Potters Bar, UK.
Shorrocks, V.M. (undated): Boron deficiency: its prevention and cure. Borax
Holdings Ltd., London.
Sieling, E.R.M. (1992): Stikstofbemestingsrichtlijnen voor de akkerbouw ende groenteteelt in de vollegrond. Informatie en Kennis Centrum voor de
Akkerbouw en de Groenteteelt in de vollegrond, Lelystad, The
Netherlands.
Sommer, K. (1991): Stickstoffversorgung von Gemisepflanzen auf
Ammonia-Basis unter besonderer Berucksichtigung der Jungpflanzenanzucht. Agrikulturchemisches Institut der Rheinischen FriedrichWilhelm-Universitat Bonn.
Soorsma, H.E. (1992): Het stikstofbijmestsysteem voor vollegrongsgroenten: inzicht in bernesting. Meststoffen 1992, 16-20.
Sorensen, J.N. (1993): Use of the Nmin method for optimization of vegetable
nitrogen nutrition. Acta Hort. 339, 179-192.
Sprague, H.B. (Ed.) (1964): Hunger signs in crops. 3rd Ed. David McKay,
New York.

98

Stone, D.A. and Rowse, H.R. (1992): Reducing the nitrogen requirement ofvegetable crops by precision fertilizer injection. Aspects of Applied
Biology 30, 399-402.
Terman, G.L. (1979): Volatilization losses of nitrogen as ammonia from'surface-applied fertilizers, organic amendments, and crop residues. Adv.
Agron. 31, 189-223.
Thorne, W. (1957): Zinc deficiency and its control. Adv. Agron. 9, 31-65.
Truog, E., Berger, K.C. and Attoe, O.J. (1953): Responses of nine economic
plants to fertilization with sodium. Soil Sci. 76, 41-50.
Tsai-fua Chiu (1975): Calcium mobility studies in plants with particularreference to nutritional disorders. Ph.D. Thesis, Univ. Bristol, U.K.
Van der Paauw, F. (1971): An effective water extraction method for thedetermination of plant-available soil phosphorus. Plant and Soil 34, 467481.
Venter, F. (1984): Nitrate contents of head lettuce as influenced bynitrificides. Acta Hort. 163, 23 1-236.
Vesanto, T. and Lehtimliki, S. (1993): Horticulture in Finland. Agric.
Economic Res. Inst. Research Publications No. 71.
Vogtmann, H., Matthies, K., Kehres, B. and Meier-Ploeger, A. (1992):
Enhanced food quality induced by compost applications. Proc. Intern.
Composting Res. Symp., Columbus, Ohio, USA; March 27, 1992.
Wallace, T. (1961): The diagnosis of mineral deficiencies in plants by visual
symptoms. H.M.S.O., London.
Wedler, A. (1985): Einfluss der Diingung auf die Qualitat von Gemose.
Deutscher Gartenbau 39, 642-644.
Williams, D.E. (1961): The absorption of potassium as influenced by its
concentration in the nutrient medium. Plant and Soil 15, 387-399.
Wright, J. (1994): A decade of field vegetables. The Horticulturalist 3, 8-12.
Yadav, B.R. and Tomar, S.P.S. (1990): Comparative effect of chloride andsulphate salinity in irrigation water on yield and mineral nutrition of
cauliflower (Brassicaoleraceavar. Botrytis). Vegetable Sci. 17, 191-194.
Zehler, E., Kreipe, H. and Gething, P. (1981): Potassium sulphate andpotassium chloride. Their influence on yield and quality of cultivatedplants. IPI-Research Topics No. 9. International Potash Institute, Bern.
Zinc in Crop Nutrition (undated): International Lead Zinc Organization,Inc., New York.

99

References (Chapter 8.2)
Barber, S.A. (1984): Soil Nutrient Bioavailability. Wiley-Interscience. New
York.
Bar-Tal, A., Bar-Yosef, B. and Kafkafi, U. (1990): Pepper transplant response
to root volume and nutrition in the nursery. Agron. J. 82: 989-995.
Bar-Tal, A., Pressman, E. and Rylska, E. (1994): Tomato response to K-Ca
ratios and root restriction in solution culture. Annual report submitted to
CALAR tri-national (Egypt, US, Israel) project.
Bar-Yosef, B. (1971): Fluxes of P and Ca into intact corn roots and theirdependence on solution concentration and root age. Pl. Soil 35: 589-600.
Bar-Yosef, B., Kramer, S. and Ben-Basat, S. (1980): Trickle irrigation andfertilization in the Northern Arava valley in Israel: Bell pepper.
Agricultural Research Organization, Bet-Dagan, Israel (Hebrew).
Bar-Yosef, B., Kramer, S., Nutman, 1. and Ben-Basat, S. (1981): Trickle
irrigation and fertilization in the Northern Arava Valley in Israel: Eggplants. Agricultural Reseach Organization, Bet Dagan, Israel (Hebrew).
Bar-Yosef, B. and Lambert, J.R. (1981): Corn and cotton root growth inresponse to soil impedance and water potential. Soil Sci. Soc. Am. J. 45:
930-935.
Bar-Yosef, B. and Sagiv, B. (1982a): Response of tomato to N and water
applied via a trickle irrigation system. I. Nitrogen. Agron. J. 74: 633-737.
Bar-Yosef, B. and Sagiv, B. (1982b): Trickle irrigation and fertilization of
Iceberg lettuce. Proc. 9th Intern. Plant Nutrition Colloquium. Warwick
University, England, Vol. 1: 33-38.
Bar-Yosef, B., Kramer, S. and Ben-Basat, S. (1982): Trickle irrigation andfertilization in the Northern Arava Valley in Israel: Fresh tomatoes (cv.
675). Agricultural Research Organization, Bet Dagan, Israel (Hebrew).
Bar-Yosef, B. and Sagiv, B. (1985): Potassium supply to field crops grownunder drip irrigation and fertilization. Proc. K Symposium, International
Potash Institute, Pretoria, pp. 185-188.
Bar-Yosef, B., Sagiv, B. and Markovitch, T. (1989): Sweet corn response tosurface and subsurface trickle P fertigation. Agron. J. 74: 640-644.
Bar-Yosef, B. (1991): Vegetable production and fruit yield and quality
under combined trickle irrigation and fertilization. FAO/ECE symp. on
methods and concepts for the use of organic and chemical fertilizers.
Geneva, Jan. 1991.
Bar-Yosef, B., Matan, E., Levkovich, I., Assaf, A. and Dayan, E. (1992):
Response of greenhouse tomatoes (cv. F-144 and F-175) to irrigation andfertilization in the Besor area. Report on project 30-170-92, Agricultural
Research Organization, Israel (Hebrew).
100

Bar-Yosef, B. and Imas, P. (1995a): Tomato response to phosphorus
nutrition via drip fertigation. Proc. Fifth Intern. Microirrigation Cong.,
Orlando, FL. pp. 200-208. American Soc. Agric. Engineers.
Bar-Yosef, B. and Imas, P. (1995b): Orthophosphate solubility in waters ofdifferent ionic composition. Fertilizer Res. (in press).
Bar-Yosef., B., Keinan, M., Stembaum, B., Levkovich, I., Markovich, T.,
Rosenberg, R. and Soriano, S. (1995): Muskmelon (cv. Arava) response
to N concentration in water, NH 4 :NO 3 ratio and greenhouse temperature.
Report on project 301-0211-95, Agricultural Research Organization,
Israel (Hebrew).
Beese, F., Horton, R. and Wierenga, P.J. (1982): Growth and yield responseof chili pepper to trickle irrigation. Agron. J. 74: 556-561.
Ben Asher, J., Gordon, J.M., Liner, A. and Zarmi, Y. (1982): Nutrient uptake
and supply to tomato plants in water culture system. Agron. J. 74: 640-644.
Bresler, E. (1975): Two-dimensional transport of solutes during nonsteady
infiltration from a trickier source. Soil Sci. Soc. Am. Proc. 39: 604-613.
Bresler, E., McNeal, B.L. and Carter, D.L. (1982): Saline and sodic soils.
Springer-Verlag, New York.
Bucks, D.A., Nakayama, F.S. and Warrick, A.W. (1982): Principles, practices
and potentialities of trickle (drip) irrigation. Adv. Irrigation I: 220-298.
Cassell, D.K. and Klute, A. (1986): Water potential: tensiometry. In: A.
Klute (ed): Methods of Soil Analysis. Part I. pp. 563-596. Series inAgron. No. 9. Am. Soc. of Agron. Madison, WI, USA.
Dafne, 0. (1984): Nitrogen effect on dry matter production, mineral absorption, yield and quality of processing tomatoes. MSc thesis submitted to
the Faculty of Agriculture, The Hebrew University of Jerusalem, Israel(Hebrew).
Dasberg, S. and Bresler, E. (1985): Drip Irrigation Manual. International
Irrigation Information Center, Publication No. 9, Bet Dagan, Israel.
Feigin, A. and Sagiv, B. (1971): Broccoli response to manure and N
fertilization in a loessial soil in southern Israel. Report on project 40110102, Agricultural Research Organization, Israel (Hebrew).
Feigin, A., Sagiv, B., Aviram, H. and Zipilevich, Y. (1976): Celery response
to manure and N fertilization in a loessial soil in southern Israel. Reporton project 301-046, Agricultural Research Organization, Israel (Hebrew).
Feigin, A., Zwibell, M., Rylski, I., Zamir, N. and Levav, N. (1979): The
effect of ammonium/nitrate ratio in the nutrient solution on tomato yieldand quality. Acta Hort. 98: 149-160.

101

Feigin, A. and Sagiv, B. (1982): Dry matter and nitrogen accumulation in
irrigated autumn and spring potatoes grown in arid zone. Proc. 9th Intern.
Plant Nutrition colloq. Warwick Univ., England. Vol. I pp. 168-173.
Feigin, A., Ginzburg, C., Gilead, S. and Ackerman, A. (1986): Effect of
NH 4/NH 3 ratio in nutrient solution on growth and yield of greenhouseroses. Acta Hort. 189: 127-132.
Fishman, S. and Bar-Yosef, B. (1995): Simulation of N uptake andpartitioning in potato plants in relation to yield: Model description andsensitivity analysis. Proc. Potato simulation Workshop, Wageningen,
The Netherlands, 1994.
Fried, M. and Broeshart, H. (1967): The soil-plant system in relation to
inorganic nutrition. Academic Press, New York.
Ganmore-Neumann, Ruth and Kafkafi, U. (1980): Root temperature andpercentage N0 3/NH 4 effect on tomato plant development. 1. Morphology
and growth. Agron. J. 72: 758-761.
Ganmor-Neumann, Ruth and Kafkafi, U. (1983): The effect of root
temperature and N0 3/NH 4 ratio on strawberry plants. I. Growth,
flowering and root development. Agron. J. 75: 941-947.
Gardner, W.H. (1986): Water content. In: A. Klute (ed): Methods of Soil
Analysis. Part 1. pp. 493-544. Series in Agron. no. 9. Am. Soc. Agron.
Madison WI, USA.
Glass, A.D.M. and Perley, J.E. (1980): Varietal differences in potassium
uptake by barley. Potash Rev. 12: 1-9.
Goldberg, D., Gornat, B. and Rimon, D. (1976): Drip Irrigation Principles,
Design and Agricultural Practices. Drip Irrigation Scientific Publications,
Kfar Shmariahu, Israel.
Halevy, J. (1976): Growth rate and nutrient uptake of two cotton cultivars
grown under irrigation. Agron. J. 68: 701-705.
Hatfield, J.L. and Fuchs, M. (1990): Evapotranspiration models. In: G.J.
Hoffman, T.A. Howell and K.H. Solomon (ed): Management of Farm
Irrigation Systems. pp. 33-59. ASAE Monograph, The Arrierican Societyof Agricultural Engineers, St. Joseph, MI.
Hoffman, G.J., Rhoades, .ID., Letey, J. and Fang Sheng (1990): Salinity
management. In: G.J. Hoffman, T.A. Howell and K.H. Solomon (eds):
Management of Farm Irrigation Systems. pp. 667-715. ASAE Monograph,
The American Society of Agricultural Engineers, St. Joseph, Mi.
Jones, C.A. and Kiniry, J.R. (1986): CERES-MAIZE. A simulation model ofmaize growth and development. Texas A&M University Press. Tx.
Marani, A. and Baker, D.N. (1981): Development of a predictive dynamic
simulation model of growth and yield in Acala cotton. BSF report 1708/
78, The Hebrew University of Jerusalem, Faculty of Agriculture, Israel.
102

Martin, D.L., Stegman, E.C. and Fereres, E. (1990): In: G.J. Hoffman, T.A.
Howell and K.H. Solomon (eds): Management of Farm Irrigation,Systems. pp. 155-203. ASAE Monograph, The American Society of/ Agricultural Engineers, St. Joseph, MI.
Mengel, K. and Kirkby, E.A. (1987): Principles of plant nutrition. 4th ed.
International Potash Institute, Bern, Switzerland.
Olsen, S.R. and Kemper, W.D. (1968): Movement of nutrients to plant roots.
Adv. Agron. 20: 91-151.
Rhoades, J.D. and Oster, J.D. (1986): Solute content. In: A. Klute (ed):Methods of Soil Analysis, Part 1. pp. 563-596. Series in Agron. No 9.
Am. Soc. Agron. Madison WI, USA.
Sagiv, B., Bar-Yosef, B. and Kafkafi, U. (1977): Drip irrigation andfertilization in Besor: Bell pepper. Agricultural Research Organization,
Bet Dagan, Israel (Hebrew).
Sagiv, B., Bar-Yosef, B. and Eliah, E. (1980): Drip irrrigation and fertilizationof sping muskmelon at Besor. Special Publication no. 17. Division of
Scientific Publications, The Volcani Center, Bet-Dagan, Israel (Hebrew).
Sagiv, B., Bar-Yosef, B., Eliah, E. and Mini, A. (1983): Response of sweetcorn to trickle irrigation and N fertilization under drip and sprinkle
irrigation. Report 301/064. Agricultural Research Organization, Bet
Dagan, Israel.
Sagiv, B., Feigin, A., Hadas, A., Keinan, M. and Markovich, T. (1992):
Response of drip irrigated chinese cabbage to manure and municipal
refuse composts and inorganic N fertilization. Report on project 301154-90, Agricultural research organization, Israel.
Sagiv, B., Bar-Yosef, B., Hadas, A., Soriano, S. and Levkovich, 1. (1995):
Response of drip irrigated carrot (cv. Buror) to manure and municipal
refuse composts and inorganic N fertilization. Report on project 301154-90, Agricultural research organization, Israel.
Shevah, Y. and Waldman, M. (1989): Advances in management of fertilizer
application and the resulting effect on the pollution load in soil. In: B.
Bar-Yosef, N.J. Barrow and J. Goldshmid (eds.) Inorganic Contaminantsin the Vadose Zone. Springer-Verlag, New York. pp. 179-189.
Stanford, G. and Epstein, E. (1974): Nitrogen mineralization water relations
in soils. Soil Sci. Soc. Am. Proc. 38: 103-107.
Stanhill, G. (1985): Water use efficiency. Adv. Agron. 39: 53-85.
Tillitson, W.R., Robbins, C.W., Wagenet, R.J. and Hanks, R.J. (1980): Soilwater, solute and plant growth simulation. Utah Agricultural Experiment
Station Bulletin 502.

103

Topp, G.C. and Davis, J.L. (1985): Time-domain reflectometry (TDR) and
its application to irrigation scheduling. p. 107-127. In: D. Hillel (ed.)
Advances in irrigation. Vol 3. Academic Press, Orlando, FL.
US Salinity Laboratory Staff (1954): Diagnosis and improvement of saline
and alkali soils. USDA Agric. Handbook No. 60.
Yarwood, C.E. (1978): Water and the infection process. In: Water deficit
and plant growth. T.T. Kozlowski (ed.) 5: 141-165. Academic Press, N.Y.

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