IPI
Bulletin 8(2nd revised edition)

Ak

International Potash InstituteBasel/Switzerland

1993

IPI-Bulletin No. 8(2nd revised edition)

PotatoFertilizers for Yield and Quality
S. Perrenoud, Ing. agr.
International Potash InstituteB asel/S witzerland

gInternational

Potash Institute
P.O. Box 1609

CH-4001 Basel/Switzerland
1993

C All rights held by: International Potash Institute
P.O. Box 1609
CH-4001 Basel/Switzerland
Phone: (41) 61 261 29 22/24
Telefax: (41) 61 261 29 25

Printing: Imprimerie Brinkmann, Mulhouse/FranceContents

Page
Introduction

7

1
1.1
1.2
1.3
1.4

The importance of the potato crop
Importance in relation to other principal crops
Area planted, production and yield 1948/52 and 1989
Geographical spread of potato growing
Utilization of the crop

8
8
9
10
10

2
2.1
2.2
2.3

Nutrient requirement of the crop
Uptake of nutrients
Removal of nutrients in tubers
Pattern of nutrient uptake

13
13
13
15

3
3.1
3.1.1
3.1.2
3.1.3
3.2
3.2.1
3.2.2
3.2.3
3.2.3.1
3.2.4
3.2.5
3.2.6
3.2.7

The effects of fertilizers on growth and yield
GrowthLeaf area and photosynthesis
Tuber initiation
Other aspects of growth
Yield
NitrogenPhosphorus
Potassium
Effect of the form of potash
Magnesium
Trace elements
Nutrient interactions
Yield components

15
15
15
15
16
16
16
17
17
18
18
18
18
18

3

3.3
3.3.1
3.3.2
3.3.3
3.3.4
3.3.5
3.3.6
3.3.7

Factors affecting yield response to fertilizers
Variety
Planting density
Previous cropping
Soil nutrient content
Soil moisture
Farmyard manure
Duration of experiments

21
21
22
22
22
22
26
26

4
4.1
4.1.1
4.1.1.1
4.1.1.2
4.1.1.3
4.1.1.3.1
4.1.1.4
4.1.2
4.1.3
4.1.3.1
4.1.3.2
4.1.3.3
4.1.4
4.1.4.1
4.1.4.2
4.1.4.3
4.1.4.3.1
4.2
4.2.1
4.2.1.1
4.2.1.2
4.2.1.3
4.2.1.3.1
4.2.1.4
4.2.2
4.2.2.1
4.2.2.2
4.2.2.3
4.2.2.3.1

Effects of fertilizers on quality
Superficial properties of tubers
Tuber size
NitrogenPhosphate
Potassium
Form of potash fertilizer
Magnesium
Tuber weight
Mechanical damage to tubers
Effect of nitrogen
Effect of phosphorus
Effect of potassium
Tuber colour (internal blackening)
Effect of nitrogen
Effect of phosphorus
Effect of potassium
Effect of form of potash
Tuber composition
Dry matter content
Effect of nitrogen
Effect of phosphorus
Effect of potassium
Effect of form of potash
Effect of magnesium
Starch content
Effect of nitrogen
Effect of phosphorus
Effect of potassium
Effect of form of potash

26
26
26
27
28
28
28
29
29
30
30
30
30
31
31
32
32
34
35
35
35
36
36
38
38
38
38
41
41
43

4

4.2.2.4
4.2.3
4.2.4
4.2.4.1
4.2.4.2
4.2.4.3
4.2.5
4.2.6
4.2.7
4.2.8
4.2.9
4.3
4.3.1
4.3.2
4.3.3
4.3.3.1
4.3.3.2
4.3.3.3
4.3.3.3.1
4.3.4
4.4
4.5

Effect of magnesiumSpecific gravity of tubers
Protein content
Effect of nitrogen
Effect of phosphorus
Effect of potassium
Reducing sugar content
Lipid content
Fibre content
Vitamin content
Alkaloid content
Cooking quality of tubers
TextureFlavourAfter-cooking blackening
Effect of nitrogen
Effect of phosphorus
Effect of potassium
Effect of form of potash
Crisp colour
Storage behaviour
Summary of effects of fertilizers on quality

43
43
44
44
45
45
46
46
47
47
47
48
48
49
50
50
50
50
51
51
52
52

5
5.1
5.2
5.3
5.4
5.5

Effects of fertilizers on plant health
Fungal diseases
Bacterial diseases
Virus diseases
Physiological disorders
Cold

53
53
55
56
56
56

6
6.1
6.2
6.2.1
6.2.2

Method and timing of applying fertilizers
MethodTiming of application
Nitrogen
Potassium

57
57
58
58
60

5

7
7.1
7.2

Nutrient deficiencies
Deficiency symptoms
Varietal differences

61
61
61

8
8.1
8.2

World fertilizer practice
Recommendations
Fertilizer practice

64
64
64

9

Appendices65
Appendix 1: Mean effect of nitrogen on yield
65
Appendix 2: Mean effect of phosphorus on yield
66
Appendix 3: Mean effect of potassium on yield
68
Appendix 4: Fertilizer recommendations (kg/ha N, P205, K20)
in various countries
72
Appendix 5: Fertilizer rates (kg/ha N, P205, K20) used invarious countries
76

10

Bibliography

677

Introduction
The potato is an important food crop, more particularly in the temperatezone, especially in Europe and the USSR. Between 1950 and 1989, the cultivated area decreased by 20% but production increased by 12% because average yield increased from I I to 15.3 tlha. The crop is demanding of soil
nutrients and has a particularly high requirement for potassium - the tubers
remove 1/ times as much potassium as nitrogen and 4 or 5 times the amountof phosphate. For instance a yield of 37 t/ha (average over 23 French
experiments) removed 113 kg N, 45 kg P205 and 196 kg K20 per hectare.
The quantity of nutrients taken up by a crop is not necessarily an indicationof responsiveness to fertilizers but the potato, because its root system is relatively poorly developed in relation to yield is extremely responsive to all
nutrients. For this reason it has been widely used in field experiments designed to compare the nutrient requirements of different soil types and ofsoils in relation to soil analysis. Thus, there is available a mass of data fromfield experiments reaching back over many years. Though most of our information of practical importance concerning the fertilizer needs of the potato
was available many years ago, we confine ourselves in this bulletin to recent
literature, much of which, it must be admitted, only serves to confirm what
was known earlier. This limitation means that where there has been relatively
little investigation of a particular problem during recent years the reader may
receive an unbalanced impression of the balance of the evidence and he isadvised to consult earlier publications as for instance "The Manuring of
Potatoes" by G. Gruner (1963).
Chapter I deals with the general points of the importance of the crop, geographical distribution, potential and actual yields and utilization.
Chapter 2 is concerned with the nutrient requirements of the crop as
indicated by total uptake in tubers and above-ground parts and the pattern of
uptake through the growing season (3.3) which indicates that there are
critical periods during which nutrient uptake is particularly rapid, imposing astrain on soil reserves, and as indicated by removal in the tubers (3.2) whichindicate the quantities of nutrients which should be applied to maintain soil
fertility.
Chapter 3 is concerned with effects on yield, commencing (3.1) withdiscussion of crop development, it then deals (3.2) with the effects of theindividual major elements and trace-elements and, most importantly, with
their interactions (3.2.6) on tuber yield. Section 3.3 discusses how fertilizer

7effects may vary with such factors as cultivar, planting density, rotation, soil
type and the availability of water.
Chapter 4 is devoted to effects on the quality of the crop. This is a complex
matter, some aspects of tuber quality being superficial, such as tuber size andweight, susceptibility to mechanical damage, but nevertheless important;other aspects of quality are indicated by tuber composition which can be
described quantitatively by analysis; yet other aspects of quality, such as
taste are only subjective. The whole question is complicated by the fact thatthe desired quality varies according to the purpose for which the potatoes are
required (e.g. table, processing industrial or seed) and that it is subject verymuch to personal preference.
Chapter 5 deals with the effects of fertilizers on disease and pest resistanceand tolerance of, or ability to combat, physiological stress.
Time and method of application of fertilizer can have important effects as
discussed in Chapter 6.
Because they may be useful in diagnosing troubles, the principal nutrient
deficiencies are described in Chapter 7.
The potato being such a demanding crop, it is particularly necessary that thefertilizers used should be correctly balanced. Applying the correct quantity ofbalanced fertilizer is the first requirement for achieving optimum yield anddoing so will give potatoes of acceptable quality.
The object of this booklet is not to give recommendations for fertilizers
which must vary greatly according to local conditions. Rather, it is to discussvarious aspects of fertilizer effects from a consideration of the recent
literature. It is hoped that this discussion will be helpful to those who are
engaged in investigating problems of the potato crop by providing asummary of recent world literature.

1

The importance of the potato crop

1.1. Importance in relation to other principal crops
In terms of area planted, the potato is the twelfth most important crop in theworld (18.07 million hectares in 1989, Table 1); in terms of total production
it occupied 6th position at 277 million t, between sugar beet (306 mio.) andbarley (169 mio.). It is a high yielding crop, the world average being 15.3
t/ha, the third highest yielding crop, on the basis of fresh matter, after sugar
cane (60.2 t/ha) and sugar beet (35.6 t/ha).

8

1.2. Area planted, production and yield 1948/52 and 1989
Between 1948/52 and 1989 the total world area planted declined by 20%(Table 2). While the importance of the crop declined more or less markedly
in Europe, the USSR and N. and C. America, there has been some increase in
S. America and the area planted in Africa has more than doubled.

Table 1. Area planted, yield and production of principal crops in the worldin 1989 (FAO, 1989)
Crop

Wheat
Rice
Maize
BarleySoya
Sorghum
MilletCottonDry beans
Oats
Groundnuts
PotatoSugarcane
Sugarbeet

Area planted

Yield

Production(1000 ha)(t/ha)(1000 t)22595114645512966471 962
58298
44441
37464
32 19326974
23 16720 093
18070
16723
8599

2.4
3.5
3.6
2.3
1.8
1.3
0.8
1.5
0.6
1.8
I.1
15.3
60.2
35.6

538056506291470318168 964
107350
57976
30512
49085
15 87242 19722 594276 740
1 007 184
305 882

Despite the shrinking area, world production has actually increased by 12%
in the same period, production now being higher in all regions except Europe
and the USSR. This increase in production has been due to a general
improvement in yield from II to 15.3 t/ha (+39%) but, though this increaseis considerable, it is not so great as the increase in yield by the principal
cereals (Table 3).

9The potential yields of present-day varieties, estimated at 85-100 t/ha forpotato, 75-85 t/ha for beet and 12-15 t/ha for wheat (Evans, 1977) are far
above the yields commonly obtained in practice. World average yields in1989 were only 1/6 of the potential for potato, 1/6 for wheat and 2/5 forsugar beet. However, yields of 85 t/ha or more have already been obtainedon the "blue-print" system in England (Evans, 1977).

1.3. Geographical spread of potato growing
Europe and the USSR together produced 63% of the total world crop in
1989, but the crop is very widely grown in every continent altogether in over
100 countries (FAO, 1989). Only 27 countries grow more than 100'000 ha(Table 4), and 67% of the crop is grown in 6 of them: USSR, Poland, China,
Germany, the USA and India, in descending order. Mean yields varyconsiderably between countries, from 5.2 to 41.5 t/ha for the countries listed
in Table 4, the highest yield being in the Netherlands.

1.4. Utilization of the crop
A major part of potato production is usually used for human consumption.
Human consumption of potatoes has however declined in the industrializedcountries as the standard of living has increased. In these countries, an increasing proportion of the crop is used for the manufacture of products suchas crisps, oven-ready chips, dehydrated potato powder.
Thus, in West Germany the consumption of fresh potatoes per head decreased from 157 kg in 1954/55 to 92 kg in 1974/75 whereas theconsumption of processed potatoes increased from I to 15 kg/head during
this period (Bittelmann, 1974).
In temperate regions, there is a distinction between early potatoes, planted as
early as possible in the spring and harvested early to get a high price, andmaincrop potatoes which are harvested later and give a higher yield due tothe longer growing period but which attract a lower price.
Another major use for potatoes is as stockfeed, mainly for pig fattening. Besides this potatoes are also used by industry, especially for starch production.
Finally, since up to about 10% of the harvest is needed for seed, the production of seed potatoes is very important in areas suitable for this purpose.

10

Table 2. Area planted, yield per hectare and total production of potatoes for the world and by regions
1948/1952 and 1989 (FAO, 1970; FAQ, 1989)
Area planted (1000 ha)
Yield (t/ha)
1948/52 1989
Change 1948/52 1989
9501
4790 - 50% 13.7215
8574
6200 - 28%
9.4
11.6
2625
4607 + 76%
6.9
13.3

EuropeUSSR
Asia

North and Central America
South America
AfricaOceania
World

Production (1000 MT)
Change 1948/52
1989
Change+ 57% 130 155 102984 - 21%
+ 23%
80239
72000 - 10%
+ 93%
18000
61416 +241%

852
740
224
60

735
912
779
48

- 14%
+ 23%
+248%
- 20%

15.0
6.0
5.7
10.2

28.4
12.6
8.6
27.7

+ 89%
+110%
+ 51%
+172%

12741
4431
1 266
609

22576

18070

- 20%

11.0

15.3

+ 39%

247440 276440 + 12%

Table 3. Mean yield of several crops 1948/52 and 1989 (FAO, 1970, FAO, 1989)
Crop
Wheat
Rice
Maize
Sugarbeet
PotatoAverage yield (t/ha)
1948/52
1989
1.0
2.4
1.6
3.5
1.6
3.6
21.3
35.6
11.0
15.3

Increase %
140%
119%
125%
67%
39%

20837
11 453
6722
I 328

+ 64%
+158%
+431%
+118%

Table 4. Area planted and yield in the main producing countries in 1989
(FAO, 1989)
Country

Area planted (1000 ha)

Yield (t/ha)

AfricaAlgeria120

8.6

North America
Canada
USA

112
518

24.6
32.2

South America
Argentina
Bolivia
BrazilColombia
Peru

112
127
156
175
19.3

23.2
5.2
13.5
15.7
8.8

Asia
Bangladesh
China
India
Iran
Japan
Korea (Dem. Rep.)
Turkey

121
2 602
918
105
123
155
190

10.3
I1.5
15.8
13.3
30.1
13.2
20.5

EuropeCzechoslovakia
FranceGermany
Italy
Netherlands
PolandPortugal
Romania
Spain
United Kingdom
USSR
Yugoslavia
Total

170
190
649
127
165
1 858
123
325
274
178
6200
294
16280

18.6
30.3
26.2
20.2
41.5
18.5
8.8
22.2
19.1
35.8
11.6
8.0

12

2.

Nutrient requirements of the crop

2.1. Uptake of nutrients
Potassium is the nutrient taken up in the greatest quantity; the crop also takes
up much nitrogen and appreciable amounts of calcium, phosphorus, magnesium and sulphur.
Maximum uptakes by different varieties in Japan range between 91 and 120
kg/ha N, 32 and 55 kg/ha P205 and 140 and 267 kg/ha K20 (KALI KENKYU KAI, 1980). In England, potatoes grown on the 'blueprint' system andgiving the very high yield of 77.7 t/ha took up 350 kg/ha N, 95 kg/ha P205
and 450 kg/ha K20 (Anderson and Hewgill, 1978). Brazilian experimentswith 6 varieties showed the following uptakes (kg/ha N, P205, K20, CaO,
MgO, S): nitrogen 102-166, phosphorus 30-62, potassium 207-367, calcium
37-80, magnesium 16-25 and sulphur 17-38.

2.2. Removal of nutrients in tubers
The tubers remove much potassium, usually 12 times as much as nitrogenand 4 or 5 times as much as phosphorus. Removals of magnesium, sulphur
and calcium are much less but still significant.
23 experimental crops in France (Lou6, 1977) giving a mean yield of 37.3
t/ha tubers removed in the tubers on average: 113 kg N, 45 kg P205, 196 kg
K20, 7 kg CaO and 13 kg MgO, respectively 3.0, 1.2, 5.2, 0.2 and 0.3 kg per
tonne tubers (Figure 1). Motta Macedo (1976) reports the following
removals in kg/ha for 6 varieties grown in Brazil: N: 55-81, P205: 23-41,
K20: 118-192, CaO: 5-14, MgO: 4-7 and S: 9-21. 14 experiments in the
Punjab-India (Grewal and Singh, 1979) gave a mean yield of 28.75 t/ha
tubers which removed an average of 91 kg/ha K20.
At very high yield levels, nutrient removal in tubers is very high andAnderson and Hewgill (1978) report a yield of 90 t/ha, obtained at Stockbridge House in 1973 which contained in the tubers 306 kg N, 93 kg P205
and 487 kg K20.
So far as concerns trace-elements, Wiliams et aL (1960) cited by Harris(1978) report that a 20 t/ha crop at Rothamsted removed 44 g copper, 42 g
manganese, 0.74 g molybdenum and 99 g zinc. Motta Macedo (1976) reports
removals of 273-1121 g Fe and 2-17 g copper per hectare.

13

Removal (kg/ha)
200

150

,Mt

100

N

P20 5

1(20

NuteOtCa

Removal of nutrients in tubers.

Fig. I.

Total uptakelkglhaJ1/......'N

.....

300

44 - 5N
Fig. 1.200 Remvlm

7252
o

86

ttsl

V1

100

Nutrient

inuertuts.

yrptruhhesn

50,

14 10050

44
Fig. 2.

14

58

72

86

100

114

128

142

Days afterp~

Development of total nutrient uptake by crop through the season.

2.3. Pattern of nutrient uptake
Harris (1978) studied the uptake of nutrients during growth in an English
experiment (Gunasena, 1969) and his results for total uptake (tubers + tops)
are illustrated in Figure 2. Uptakes of nitrogen, phosphorus and potassium
reached a maximum 128 days after planting.
Ezeta and McCollum (1972) in Peru observed that daily uptake rates were ata maximum for nitrogen between 95 and 137 days from planting and forpotassium between 95 and 116 days. At this critical time, the crop took up
2.5 kg N and 6.6 kg K per ha per day.

3.

The effects of fertilizers on growth and yield

3.1. Growth
3.1.1. Leaf area and photosynthesis
Gunasena and Harris (1971) showed that nitrogen considerably increased
leaf area index and leaf area duration. A similar beneficial effect of nitrogenon leaf area index was also observed by Kushizaki (1975) and Ngugi (1972)(cited by Harris, 1978). Kushizaki (1975) also noted a favourable effect ofphosphorus on leaf area index. Gunasena and Harris (1971) found thatpotassium increased leaf area index and leaf area duration, though the effectwas less than that of nitrogen. Kushizaki (1975) and Haeder and Forster(1974) also found a favourable effect of potassium on leaf area index.
Goncharik and Urbanovich (1971, cited by Smith, 1977) showed that photosynthetic rate was reduced in nitrogen deficiency. Haeder et aL (1973) and
Haeder and Forster (1974) found that potassium favoured photosynthesis andthe translocation of assimilates from leaves to tubers.
3.1.2. Tuber initiation
Gunasena and Harris (1971) mentioned that tuber initiation was retarded by
the application of 220 kg/ha N at planting in the variety Craig's Royal (early)
though the main crop variety Pentland Dell was not similarly affected.
Krauss (1980) showed in solution culture that tuber initiation was inhibitedwhen N was supplied continuously (N concentration in the solution kept
above I mmol/1), but took place when the N supply was discontinuous (Nsupplied for 3 days followed by 6 days without N). Similar results fornutrient solution culture were cited by Krauss and Marschner (1976) and
Sattelmacher and Marschner (1979).

15

Gunasena and Harris (1971) could find no definite effect of potassium on
tuber initiation with Craig's Royal and Pentland varieties.
3.1.3 Other aspects of growth
Gerdes et al (1975) found that N fertilizer lengthened the growing period
expressed as days from planting to leaf senescence. Kudelja and Wirsing(1976) mentioned that maturity was delayed by the application of N fertilizer
particularly in years with dry periods during growth of the crop.
Haeder et al. (1973) observed that potassium increased the ratio tubers: topsand Haeder and Forster (1974) showed that plants adequately supplied with
K were better able to utilize available water (Figure 3).
gH,O/g dry matterO
30o

Tuber (until
maturity)

Plant(until
flowering)

200
100

Fig. 3.
potatoes.

Kconcentration
me/I)
2.0
0.4
2.0
0.4
Effect of K concentration in nutrient solution on water economy of

3.2 Yield
The mean effects of nitrogenous, phosphatic and potassium fertilizers on
tuber yield derived from series of experiments comprising a minimum of ten
annual results are listed in Appendix Tables 1-3.
3.2.1 Nitrogen
From Appendix Table I which contains a total of 936 experimental results(792 from 6 developed countries and 144 from 7 developing countries), it
can be calculated that applying up to 100 kg/ha N increases yield on the
average by 20% (Table 5), while 101-200 kg increases yield by 32% and201-300 kg by 36%. Expressed as kg tubers per kg N applied, the response is76, 61 and 49 when N is applied at 1-100, 101-200 and 201-300 kg/ha.

16

Table 5. Mean effects of nitrogen, phosphorus and potassium on yield
derived from appendices 1-3

kg N/ha
1-100
101-200
201-300
kg P2Os/ha
1-100
101-200
201-300

Mean yield increase%kg tubers/kg nutrient

20 (205)
32 (844)36( 96)76 (285)
61 (844)49( 96)7(221)
10(424)9(32)30(298)22 (439)
11 ( 32)

14 (726)
10 (621)
11 (213)32 (769)
16(634)13(201)kg K20/ha

l-100
101-200
201-300) No. annual results

3.2.2 Phosphorus
610 experimental results (466 from 4 developed countries and 144 from 7
developing countries) are presented in Appendix 2. Applying up to 100 kg/ha
P205 increased yield by 7%, 101-200 kg/ha by 10% and 201-300 kg/ha by
9% as compared with control (Table 5). The average returns per kg P205
applied are 30, 22 and II kg tubers with 1-100, 101-200 and 201-300 kg/ha
P205.

3.2.3 Potassium
1267 experimental results (607 from 8 developed countries and 660 from 10
developing countries) are indicated in Appendix 3. As shown in Table 5,yields are increased by 14, 10 and 11% for rates applied of 1-100, 101-200
and 201-300 kg/ha K20, respectively. That the average effect of potassium
on yield was greater with 1-100 kg/ha K20 than with higher rates is due tothe strong effect of this nutrient in experiments carried out in several
developing countries like Korea, India and Kenya where it was tested at rates
inferior to 100 kg/ha. For instance, 77 kg/ha K20 increased yield by 66% in
South Korea (average of 56 experiments). I kg K20 produces 32, 16 and
13 kg tubers when 1-100, 101-200 and 201-300 kg/ha K20 are applied. An
example of the effect of potassium on yield is shown in Plate I.

17

3.2.3.1 Effect of theform of potash
The mean effects of the different forms of potassium fertilizer, derived froma minimum of 3 experimental results, are listed in Table 6. It appears thatwhen potash is applied at up to 200 kg/ha K20, KCI gives a higher yield than
K2SO4, while at rates above 200 kg/ha K20 the reverse is generally the case.
Superior yields from KCI, as compared with K2SO4, have also been reported
by Bruchholz (1976) and by the Cooperativa Agricola de Cotia (1980 b, c),though Garin (1979) obtained better yields with K2SO4.
3.2.4 Magnesium
Simpson et al. (1973) in Scotland report increases in yield of 500 kg/ha fromthe application of 54 kg/ha Mg (Table 7). In West Germany, Putz et al.
(1976) found that 42 kg/ha MgO increased yield by 3% on the average of 16
experiments.
3.2.5 Trace elements
Smith (1977) has reviewed the literature on this subject and concludes that
trace elements such as boron, copper, molybdenum, manganese, iron, zinc,cobalt can have favourable effects when soils are low in these elements.
3.2.6 Nutrient interactions
Loud (1977) concluded that interaction between nitrogen and phosphorus is
usually negligible, but Yadav and Tripathi (1973) and Gervy (1970) reportstrong positive interaction between N and P.
In 17 years of a long-term experiment at Aspach (France) (Lou6, 1977) positive interactions between N and K were recorded in 15 years and negative in
2. The potato crops in this experiment received regular dressings of farmyard
manure in addition to fertilizers. The mean value of the N x K interaction
over the 17 years was +2.3 t/ha tubers (Table 8). The same author mentions
other experiments in which the N x K interaction was usually positive. Yadav
and Tripathi (1973) recorded N x K interaction amounting to 4.44 t/ha tubers
in India (Table 9).
3.2.7 Yield components
The effect of manuring on the size and weight of tubers is dealt with inchapter 4. Here we are concerned with tuber number.

18

Table 6. Effects of forms of potash on tuber yield (t/ha)
Rate of K20(kg/ha)
181
542
224
108
217
325
108
217
325
ISO
280
560
152
123
246
370
200-230

KCI

K2SO4

33.2
33.8

32.8
34.2

37.6
38.3
38.1
36.9
38.3
38.2
30.3
33.78
33.48
24.4
27.83
33.7
38.6
38.6
44.6

36.9
38.5
38.7
36.2
37.0
36.8
29.6
32.45
32.88
23.3
29.83
31.8
36.9
38.6
46.5

Difference(K2SO4-KCI)
-0.4
+0.4
+1'
-0.7
+0.2
+0.6
-0.7
-1.3
-1.4
-0.7
-1.33
-0.6
-1.1
+2.0
-1.9
-1.7
0
+1.9

No. of experiments
or annual results
68

Reference
Hahlin and Johansson (1973)15
13, var. Bintje

Putz et al. (1976)
HOjmark(1977)

11, var. Saturna

Hojmark (1977)

6
5

Bruchholz et al. (1979)
McDole et al. (1978)

4
3
3

Rowberry and Ketcheson (1978)
Sharma et al. (1976)
Lou6 (1977)

3

Temme (1970b)

Table 7. Effect of magnesium on tuber yield
Yield mean of 13 experiments t/ha
23.9
23.5
24.1
24.4

kg Mg/ha
0
13.5
27
54

Table 8. Average nitrogen x potassium interaction on long term experiments
at Aspach
Treatment
K20
N
kg/ha
0
50
200
50
0
150
200
150

Yield
17 year av.
t/ha
25.6
31.8
27.4
35.9

Interaction
NxK
t/ha

Effect of K20
t/ha
6.2

2.3

8.5

Table 9. Nitrogen x potassium interaction
Treatment (kg/ha)
K20
N
0
0
150
0
150
200
150
200

Yield (t/ha) - averageof 2 experiments
21.81
23.66
33.60
39-89

Effect of K20(t/ha)

Interaction
NxK (tlha)

1.85
6.29

4.44

Table 10. Effect of rate and form of potash on tuber number per plantkg K20/ha

0
108
217
325

20

No. of tubers per plantcv. Bintje -cv. Saturna

mean of 13 experiments
K2SO4
KCI
15.0
15.0
15.0
15.2
15.5
15.5
15.4
15.2

mean of II experiments
K2S04
KCI
15.1
15.1
15.6
15.6
16.0
16.0
16.4
15.9

Gerdes et al (1975) and Gajek (1971) observed that applying nitrogen
increased tuber number per plant, while Gajek did not find a similar effect ofphosphorus. In Denmark, Hojmark (1977) found that potash slightly
increased tuber number (Table 10), while at 270 kg/ha K20, potassium sulphate gave somewhat more tubers than potassium chloride. Gajek (1971)
also reports that potassium had a favourable effect on tuber number.
3.3

Factors affecting yield response to fertilizers

3.3.1 Variety
The nitrogen response of 40 varieties has been studied in a series of experiments in Poland (Rostropovicz and Fotyma, 1978) and three groups having
high, medium or low nitrogen requirement were distinguished, the optimum
rates being 120-150, 100-120 and about 90 kg/ha N, respectively.
W. German experiments on 4 sites over three years showed that increasing
nitrogen from 80-160 kg/ha N increased yield by 2, I1 and 13%, respectively
for the varieties Astrid, Maritta and Bodenkraft (Hunnius and Munzert,
1979). 12 experiments in Norway showed that increasing the N rate from 39
to 119 kg/ha increased yield of Pimpernel, Kerrs Pink and As by 12, 17 and
22% (Baerug and Enge, 1971). Similar effects are reported by Hunnius et al.
(1971) and Grewal (1975).
Grewal and Sharma (1978b) found that the variety F-6370 was much more
responsive than other varieties to potassium (Figure 4). Ekeberg and Ronsen(1973) report similar variation in K response. In Denmark, Hojmark (1977)
found that potassium applied as KCI had a greater effect on the yield ofSaturna than of Bintje, though there was no marked difference in response
between the varieties when K was applied as K2 SO4 (Table II).
Yield increase(%)
40

F-637030
20
10Kufri Chandramukh
Kufri Sindhjr,

00

N Kufn Sheetman' ' '0 3060Fig. 4.

120150kgK 2O/ha

Effect of potassium on yield of various cultivars.

21

3.3.2 Planting density
Maximum yields were obtained at 199 kg/ha N at a density of 34 600 plants
per hectare and at 299 kg/ha N at densities of 46 100 and 64 600 (Ngugi,1972).
3.3.3 Previous cropping
Furunes (1978) in Norway found that cropping history affected the responseof potatoes to nitrogen and potassium but did not affect phosphate response(Table 12). Nitrogen fertilizer had a much greater effect when potatoes followed potatoes or a cereal than when they followed grass. In contrast, theeffect of potassium was greatest after grass.
3.3.4 Soil nutrient content
Berryman (1973) in England found that response to phosphorus depended on
soil P content, being 5 t/ha with soil P index 1-2, 3.3 t/ha at index 3 and 1.3
t/ha at index 4-5.
Beljaev (1979) in the USSR found that response to potassium depended on
soil exchangeable K content (Table 13) and similar results were obtained in
Canada (Giroux et al., 1982) and in Norway (Furunes, 1975) (Figure 5) inexperiments in which increasing the potash dressing from 120 to 240 kg/ha
K20 increased yield by an average of 1.42 t/ha at Kn values of 10 or lessbut had no effect on yield at higher soil levels. Siebold (1971) reports thatheavy dressings of potash had spectacular effects on yield on a soil which
fixed potassium strongly (Table 14).
3.3.5 Soil moisture
Soil moisture content greatly affects fertilizer response as shown by the following examples:
Gerdes (1975) in East Germany found that nitrogen response of 2 varieties at
6 sites of 3 years was increased by irrigation (Table 15). Van der Paauw(1958) in the Netherlands showed that the effect of potassium fertilizer
depended on the number of days without rain in May to July inclusive. With45 dry days, K increased the yield by 60% but with 60 dry days the corresponding increase was more than 100% (Table 16). Yadav and Tripathi(1973) found that in India irrigation increased the response to nitrogen andalso improved phosphate response and response to potassium. Rostropovicz
and Fotyma (1978) in Poland found that the efficiency of N fertilizer was
reduced by both drought and excessive rainfall.

22

Table 11. Effect of potassium on yield (relative yield) of two cultivars
kg K20/ha

0
108
217
325

Relative yield (Ko = 100)
cv.Bintje cv. Saturna mean of 13 experiments
mean of It experiments
KCI
K2SO 4
KCI
K2SO4

36.4 = 100(36.4 t/ha)
101
106
106

36.4 = 100(36.4 t/ha)
103
105
105

35.1 = 100(35.1 t/ha)
105
109
109

35.1 = 100(35.1 t/ha)
103
105
105

Table 12. Effect of nitrogen, phosphorus and potassium on tuber yield (t/ha)
as affected by previous crop
Treatment
Rate
kg/ha
N
0
N
60
P205
0
P205
34
K20
0
K20
120

Previous crop
PotatoCereals

20.62*
26.49
23.87
25.55
25.05
25.49

19.33**
25.79
22.98
24.56
23.31
24.77

(100%)(128%)(100%)(107%)(100%)(102%)

Grass(100%)(133%)(100%)(107%)(100%)(106%)

24.59***
28.12
26.02
27.50
24.63
27.71

(100%)(114%)(100%)(106%)(100%)(113%)* Average of 10 experiments** Average of 19 experiments*** Average of 10 experiments

Table 13.
Yield response (%) to applied potash as related to soil
exchangeable K content
No. of annual results

Soil content
exch. K (mg/100 g)

234
512
55

< 10
10-20
> 20

Yield response (%)
K-rate (kg K20/ha)
30
60
90
7.4
12.2
27.8
7.0
8.3
12.5
3.3
12.2
12.2

120
21.6
12.5
3.8

23

Table 14. Effect of potash fertilizer on yield on a strongly K-fixing soil
kg K20/ha
Yield (t/ha)
08.37(100%)
300
16.83 (201%)600
26.39 (315%)900
28.76 (344%)
Yield increase(% compared to K0
120kg K20/he

15

241kg K20/ha
10

Fig. 5.

DKALvalue(No.expts.)>15.0
10.1-15.0
4.0-10.0
(13)
(141
(16)
Effect of potassium on yield as affected by soil K content.

Table 15. Effect of irrigation and nitrogen fertilizer on yield (t/ha)
mm waterper

kg N/haYield (t/ha)

irrigation

kg N/ha:0
315
349
357
373

0
20
30
40

60
365(116%)416(119%)431 (121%)444(119%)150
419(133%)487(140%)510(143%)
520(139%)240
450(143%)527(151%)549(154%)560(150%)330
456(145%)533 (153%)
550(154%)563(151%)

Table 16. Effect of rainfall on yield response to potash (t/ha)
kg K20/ha

No. of rainless days from May to July
45

50

60

0

25.0(100%)24.0 (100%)20.0(100%)400

40.0(160%)

40.5 (169%)

41.0(205%)

24

Table 17. Yield (t/ha) at various rates of potash in presence and absence of farmyard
manureManure26.6
35.2 (+32%)

No manure11.0
29.4 (+167%)kg K20/ha
0200

Table 18. Development of responses to nitrogen, phosphorus and potassium in longterm experiments
Yield increase (%)

Reference

Country
Date commenced

Year

N

P205

K20

Netherlands (1918)

1918
1924
1930
1936
1942
1947
1958
1967
1974

52
61
52
64
79
104
150
138
113

I
20
27
25
20
19
23
23
0

2
113
133
245
223
426
285
223
178

Boswijk (1976)

Poland (1923)

1924-26
1953-55

24
3

12
0

42
22

Dobransky (1976)

1962-65
1972-73

65
118

44
17

85
106

Switzerland (1949)
West Germany (1959)
England (1960)

1955

58

1965

219

1973
1961

570
6

1971
1973
1960
1965
1970

232
278
to
10
43

Walther and Hofer (1980)
Kick and Poletschny (1975)
Eagle(1974)

Table 19. Mean effect (10 experiments) of phosphorus and potassium on yield in1965 and 1969
Yield (/ha)

Treatment

Nutrient
P
P
P
K
K
K

kg/ha
0
36
72
0
80
160

1965
28.0(100%)29.6(106%)30.7(107%)28.3(100%)
29.5 (104%)30-4(107%)1969
24.4(100%)26.3(108%)27.3(112%)24.7 (100%)
26.3 (106%)27.0(109%)25

3.3.6 Farmyard manure
Boyd (1959) showed that applying farmyard manure reduced response tonitrogen and phosphorus and greatly reduced the response to potassium.
Thus the responses to N, P and K in the presence of manure were, respectively 67, 29 and 22% of the responses without manure. Lou6 (1977), in a longterm experiment in France, found that farmyard manure reduced the response
to 200 kg/ha K20 from 167% without manure to only 32% with manure(Table 17). The corresponding average figures for I I years in another longterm experiment were 107 and 37% response to 209 kg/ha K20 in theabsence and presence of farmyard manure respectively.
The responses to fertilizer listed in Appendix Tables 1-3 were generally
recorded in the absence of farmyard manure.
3.3.7 Duration of experiments
Table 18 shows how responses to nitrogen, phosphorus and potassium havedeveloped over time in some long-term experiments. The effect, particularlyof potassium has increased greatly owing to soil impoverishment in the plots
which receive no fertilizer potassium. Boguszewski and Gosek (1971) compared the effects of P and K in the first and fifth years of 20 experiments inwhich potatoes were grown in rotation with other crops. Their results (Table19) showed responses of 10 and 12% to 72 kg/ha P20 5 and of 7 and 9% to160 kg/ha K20 in the first and fifth years, but yields in the 5th year wereaffected by drought which reduced differences between treatments.
4.

Effects of fertilizers on quality

4.1

Superficial properties of tubers

4.1.1 Tuber size
Potaoes grown for the table should not contain a large proportion of small
tubers, preparation of which involves a high loss in peelings. Small tubers are
removed when the crop is riddled for the market and can only be used forstockfeed. Neither should there be too many over-large and misshapen
tubers, the ideal crop consists of moderate and uniformly sized tubers andthis applies also to potatoes grown for crisping, etc. Potatoes grown for seedshould not be too large.
The effects of fertilizers on tuber size are complex; they may affect the number of tubers initiated and, hence average size; they may also affect the sizeof the individual tuber per se. As with other aspects of fertilizer response, theeffects vary much with soil fertility and with variety. In general, nitrogen andpotash tend to increase size while phosphate tends to increase number.

26

4.1.1.1 Nitrogen
Results obtained in West Germany by Hunnius and Munzert (1979) are
shown in Table 20. In this series of experiments the increase in large tubers(>55 mm) was at the expense of the medium sized, but, on one other site with
3 cultivars over 3 years increasing N from 80 to 120 kg/ha increased the proportion of tubers above 55 mm from 21 to 27% with only a very slight effecton the medium sized fraction but a large reduction (13 to 9%) in small tubers(< 35 mm). Svensson et al. (1973) in Sweden (Figure 6) found that
increasing the rate of N increased large tubers at the expense of medium
sized. Tdihtinen (1978) in Finland and Grison and Fourbet (1973) in France
have reported that increasing the rate of N increases the proportion of large
tubers (>55 mm, >45 mm respectively). In England, Archer et al. (1976)
Table 20. Effect of rate of nitrogen on tuber size distribution
kg N/ha80
120
160

35-55 mm
49
44
42

<35 mm3
3
3>55 mm48
53
55%tubers
35-55mm
60
50> 55mm40

30

c 35rm10

0>~0kg N/ha
0225Fit75

75

75
i5251
15022500

Fig. 6. Effect of nitrogen on tuber size

27

obtained 79.2% marketable tubers without N and 86.5% with 188 kg/ha N ina series of 16 experiments. In a long-term experiment at Aspach, France over
17 years, N fertilizer increased the proportion of marketable tubers(Garaudeaux and Chevalier, 1975) and Lou6 (1977), also in France, quoted 4
experiments in which N increased and one in which it decreased the
proportion of marketable tubers (>35mm). Others, e.g. Varis (1973a),
Dubetz and Bole (1975) and Vitosh et al. (1980) found that N had no effecton the proportion of large tubers (>50 or 55mm). In the USA Wilcox and
Hoff (1979) found that N increased tubers over 48 mm in one experimentand reduced it in another one.
4.1.1.2 Phosphate
In England, Archer et al. (1976) found no effect of P on the proportion ofmarketable potatoes in 16 experiments and Varis (1973a) reports that P did
not affect tuber size. But, in a pot experiment in Canada Dubetz and Bole
(1975) found that increasing the rate of P20 5 from nil to 223 kg/ha increased
the proportion of tubers above 51 mm from 42 to 51%. Loud (1977)
observed that P tended to slightly increase the percentage of marketable
tubers in 2 experiments.
4.1.1.3 Potassium
Normally potash increases the average size of tuber and, hence theproportion of marketable tubers. Archer et al. (1976) found the proportion ofmarketable tubers rose from 84.4 to 85.6 to 86.6% as K application wasincreased from nil to 188 and 282 kg/ha K20 (average of 16 experiments).
Tihtinen (1978) found the percentage of tubers above 55 mm increased from
24.7 to 26-2 when K application increased from 50 to 220 kg/ha K20(average of 6 experiments). Increases of the proportion of large tubers werealso recorded by Grison and Fourbet (1973), Ekeberg and Ronsen (1973),
Temme (1970), Mirswa et al. (1981), Soni et al. (1980) and Sadaphal et al.
(1973); but Varis (1973a) found that K did not affect tuber size.
In the long-term experiment at Aspach (Garaudeaux and Chevalier, 1975)
marketable tubers increased on the mean of 17 crops from 86.7% without K
to 90.1% when twice the amount of K removed was applied. Loud (1977)
found that K increased the proportion of marketable tubers by greater or
lesser amount in 6 out of 7 experiments in France.
4.1.1.3.1 Form of potash fertilizer
Temme (1970b) quotes 3 experiments in the Netherlands in which the proportion of large tubers (over 55 mm) was increased from 27 to 28% by
substituting K2SO4 for KCI at 200-230 kg/ha K20. 2 demonstrations in

28

Brazil (Cooperativa Agricola de Cotia, 1980b and c) showed a similar effect(KCI 80.0 and K2SO4 82.3% tubers over 40 mm at 232 kg/ha K20), while
Sadaphal et a. (1973) in India found that K2SO4 compared with KCI
reduced the proportion of tubers below 25.4 mm in one year but had noeffect in another. Grison and Fourbet (1973) found no effect of form ofpotash on tuber size (>45 mm) when the fertilizer was applied in winter.
Earlier work in the United Kingdom (Henderson, 1965; Gething, 1968;
Holmes, 1972) indicated that substituting sulphate of potash for the chloride
reduced the proportion of both very large and undersized tubers indicating aparticular advantage for sulphate of potash for the seed crop.
4.1.1.4 Magnesium
Applying magnesium to low Mg soils in W. Germany (Hunnius et al., 1977)
increased the proportion of large tubers at the expense of medium sized(Table 2 1), while Simpson et al. (1973) in Scotland found no effect of Mg on
tuber size in 13 experiments.
Table 21. Effect of magnesium on tuber size distribution (average of 2 cvs.
at 2 sites over 3 years)
kg MgO/ha<35 mm35-55 mm
>55 mm
0
12
71
17
80
13
65
22
160
12
65
23
4.1.2 Tuber weight
Increasing N application from 90 to 180 kg/ha increased the proportion of
tubers in the range 113 to 454 g (White et al., 1974); a similar favourable
effect of N on tuber weight was observed by Gajek, 1971.
In W. Germany, Bachtaler and Hunnius (1971) found that rate of P fertilizer
had no effect on the average tuber weight but Gajek (1971) found that P fertilizer increased tuber weight.
Variable effects of K fertilizer on tuber weight have been reported. Thus,
McDole (1978) and McDole et al. (1978) found in one experiment that
applying 280 kg/ha K20 increased the proportion of tubers over 113 g while
the form of potash (KCI or K2SO4) had little effect and in another that
applying 168 kg/ha had no effect on tuber weight, while applying double thisrate reduced the proportion over 113 g and that the form of potash waswithout effect. White et at (1974) report that increasing K fertilizer
increased the proportion of tubers between 113 and 454 g, while Gajek(1971) found no effect on tuber weight. In India, Sharma et al. (1976) and29

Grewal and Sharma (1980) found in 4 experiments that K fertilizer increased
the proportion of tubers over 75 g, while the form of K had no effect.
4.1.3 Mechanical damage to tubers
Mechanical damage during harvesting reduces the value of potatoes and is a
cause of loss in storage.
4.1.3.1 Effect of nitrogen
Hunnius and Bachthaler (1977) in West Germany found that mechanicaldamage was slightly reduced by applying N as calcium ammonium nitrate
but that when a mixture of this with calcium cyanamide was used damage
was increased; these experiments covered 2 sites and 2 varieties over 3 years.
Bbhmig et al. (1975) in East Germany found that increasing N tended toincrease susceptibility to damage but that the effect varied with season(experiments at 6 sites with 2 varieties over 2 years). Varis (1972) found that
increasing N reduced resistance of the skin.
4.1.3.2 Effect of phosphorus
Hunnius and Bachthaler (1977) - 3 years trials on 2 sites with 2 cultivars found that a high rate of P fertilizer reduced damage, % damaged tubers
being 23.5, 24.4 and 21.7 at 0.80 and 160 kg/ha P205. Similarly, Fivkov(1978) in the USSR found that applying 120 kg/ha P205 reduced damage inmechanically harvested potatoes.
4.1.3.3 Effect of potassium
Hunnius and Bachthaler (1977) found on a soil well supplied in potassiumthat increasing the K dressing markedly reduced damage from 33.9% without
K fertilizer to 24.7% with 270 kg/ha K20 (Figure 7). Damage was also
reduced by applying 120 kg/ha K20 in the Russian experiments mentioned
above.
%damaged tubers

33

90
10
20
npretdaae
c fptssu
Fig.~~~~~~~~~~~~.......
N3.......

27....
ues(veaeoer)4.1.4 Tuber colour (internal blackening)
The effect of nitrogen and potash fertilizers on internal blackening has beenstudied by many workers. The blackening is caused by the oxidation of phenolic substances, notably tyrosine and melanine, which takes place during
handling or when the tubers are cut or peeled. The dark patches, grey-blue toblack, appear two to three days after the cells have been damaged and Wegener et al. (1979b) have shown that their incidence is increased when tyrosineand dry matter contents are high. The condition is variously described by different authors as black spot, internal blackening, enzymatic blackening or
browning.
4.1.4.1 Effect of nitrogen
Rinno et al. (1973) in East Germany found that increasing nitrogen had an
unfavourable effect on the colour of juice expressed from the tubers and thattyrosine content of the tubers was raised (Table 22). In Finland Tahtinen(1978) found that uncooked tubers 24 hours after cutting showed a darker
colour as the N rate increased from 50 to 150 kg/ha N (Table 23). On theother hand, in East Germany, Ziinker et al. (1975) found that nitrogen tended
to reduce blackening in 2 years out of 3. Lou6 (1977) found that nitrogen
fertilizer reduced blackening in tubers stored without riddling but increased it
when they were riddled before storing:% tubers affected by internal blackening
N applied(kg/ha)75
225
no riddling
92.9
86.0
riddled
15.9
28.9
Enge and Bacrug (1971) and Rostropovicz (1978) report that nitrogen adversely affected colour of tubers and Ciecko (1974b) found that N increased
blackening of tubers juice. On the other hand Wegener et al. (1979a)
observed that N had no effect.
Table 22. Effect of nitrogen on juice colour and tyrosine content of tubers(mean of 7 experiments)
kg N/haJuice colour
Tyrosine content of tubers (mgl100 g)
0
40
50
40
43
60
80
46
74
120
56
78
160
62
77

31

Table 23. Effect of nitrogen on tuber colour (averages of 14 experiments)
kg N/haTuber colour*

50
150

5.1
4.6

* Scored from I to 9; l=entirely black, 9=absence of blackening

4.1.4.2 Effect of phosphorus
Phosphorus appears to have no effect (Ciecko, 1974b).
4.1.4.3 Effect of potassium
There is much evidence that potash fertilizer reduces susceptibility tointernal blackening. In 4 long-term experiments in East Germany (Rinno etal., 1972), potassium improved colour of tuber juice, decreased tyrosin
content of tubers and increased their chlorogenic acid content (Table 24).
They also found in the 7th year of a long-term experiment that potassiumcounteracted the effect of nitrogen in increasing internal blackening. The
results for tubers receiving 140 kg/ha P205 are presented in Figure 8.
Prummel (1981) reports a decrease of the index of internal blackening (=1/6 x%, [light +2x moderate +3x strong blackening]) from 10.7 without K to 7.3
and 5.1 with 300 kg/ha K20 applied as KCI in autumn or winter (average of
43 experiments). In England, on a soil low in potassium (Anon., 1977), thepercentage of tubers of 57 to 70 mm showing internal blackening was 34.8%
without K and 24.9 and 26.2% with 251 kg/ha K20 as KCI and K2SO4(average of 2 cv. over 2 years). Potassium also somewhat reduced thenumber of surface bruises-

Table 24. Effect of potassium on juice colour of tubers and on tyrosine andchlorogenic acid content (average of results obtained in 4th-6th year of 4
long-term experiments)

32kg K20/ha

Juice colour

Tyrosine content(mg/l O0 g)

Chlorogenic acid content(mg/lO0 g)

0
80
160
320

73
60
47
51

135
111
78
81

3.5
4.5
3.7
4.4

Juice colour

KG

60o
50K
40.

30

.

K20/ha.232kg20
100Fig. 8.

'
50

'
100

5'

150

Lkg Nlha

Effect of nitrogen and potassium on juice colour of tubers.

According to Palmer and Stevens (1980), potassium applied in autumn or 68 weeks before planting considerably reduced the percentage of tubers of 6070 mm with internal blackening in a 4 year experiment on a soil low in K
(Table 25). Loud (1977) also reports that potassium greatly reduced internal
blackening (Table 26).
Grison and Fourbet (1973) from France quote % blackened tubers as 37.9,
33.7 and 29.4 from plots receiving 0, 150 and 300 kg/ha K20 respectively.
From the Netherlands, Prummel (1973) and Temme (1970b) both report afavourable effect of K fertilizer in reducing blackening. Kunkel et al. (1973)
mention that in experiments carried out over 16 years in the USA, K almost
always reduced blackening. On the other hand Tihtinen in Finland (14experiments) and Enge and Baerug (1971) in Norway found on soils rich inK that potash fertilizer had no effect. Dwelle et al. (1977) in the USA reportno effect in two experiments but a favourable effect of potash in a third on asoil with a lower K content. Birkmann (1974) and Mirswa et al. (1981) also
found that K fertilizer reduced internal blackening and Ciecko (1974b)
mentions that K application reduced the blackening of tuber juice. In longterm experiments reported by Bacrug and Enge (1974) and Wegener et al.
(1979a) K improved tubers colour. Several workers have related theincidence of internal blackening to the K status of the crop. In the
Netherlands, Alblas (1973) and Van Loon and Meijers (1973) both mention
that the susceptibility to internal blackening is reduced as soil K content
increases. The former also examined leaf K content and found that the33percentage of slightly or non-affected tubers ranged between 7 and 27%
when leaf K content was below 0.4% and between 91 and 93% at leaf
contents above 0.5%. Aeppli and Keller (1978) in Switzerland found by
examining 132 samples of different cultivars that susceptibility to blackening
increased as tuber dry matter content rose and K content decreased and thiswas confirmed in later experiments at 5 sites with 4 varieties (Aeppli and
Keller, 1979). Prummel (1969) reports that internal blackening decreased
with increasing tuber K content, as illustrated in Figure 9; this was confirmed
by Prummel (1982). Vertregt (1968) mentions that, in general, tubers with a
K content below 2% were very susceptible to internal blackening while theincidence was nil or very slight at tuber contents above 2.5% K.
4.1.4.3.1 Effect ofform of potash
In England (Anon, 1977) KCI was more effective than K 2SO 4 in reducing
internal and superficial blackening, the results concerning internal
blackening are shown in Table 27. In the Netherlands blackening was also
more reduced by KCI (Temme, 1970), but in the USA, on a low K soil,
Dwelle et al. (1977) found K2SO4 to be the more effective.
The effect of potash and of the form of potash on internal blackening is illusstrated in Plate 2.
Table 25. Mean percentage of tubers (60-70 mm) affected by internal blackening(1976-1979)
Time of application
Autumn
6-8 weeks before planting
At planting

kg K20/ha
0
33.2
33.5
31.0

200
20.4
22.5
28.4

400
15.1
19.6
27.3

600
12.1
13.9
24.2

Table 26. Effect of potash on internal blackening
Trial

Omi6court
1965

Omidcourt
1971

34

kg K20/ha

0
150
300
450
0
120
240
360

Tubers not riddled% not% severely
affected
affected
41.4
27.3
86.7
4.0
91.4
0.3
94.0
1.3
49.6
25.6
81.2
5.7
86.3
0.0
92.9
0.0

Tubers riddled% not% severely
affected
affected
16.0
59.7
28.0
25.3
44.6
14.7
56.0
6.0
14.6
45.2
14.3
31.5
30.6
13.1
25.4
15.2

Table 27. Effects of KCI and K2 SO4 on internal blackening (% affected) of tubers(57-70 mm) (mean of 2 cvs. over 2 years)
Form of potassiumkg K20/ha
KCI
K 2 SO 4

0

126

251

377

502

628

34.8
34.8

30.3
30.9

24.9
26.2

17.0
23.4

13.3
18.2

12.8
19.6

%tubers affected by internal blackening

100-

50

*

•

0
°, p Tuber Kcontent(%)
1.5
2
2.5
Fig. 9. Tuber K content and percentage of tubers affected by internal blackening.
4.2

Tuber composition

4.2.1 Dry matter content
High dry matter content is particularly to be desired in potatoes for processing (crisp manufacture, oven ready chips, dehydrated potatoes).
4.2.1.1 Effect of nitrogen
Except for MUller (1977b) who found in pot experiments that increasing
nitrogen application increased dry matter content, all other reports show that
nitrogen reduces dry matter content. There are very many results to thiseffect and we mention here only those which appear to be of major
importance. Dry matter content was reduced by 1% by 120 kg/ha N in
Norway, as shown in Table 28 (Furunes, 1975). Norwegian results are also
discussed by Bacrug and Enge (1971): In one series of trials with 3 cultivars
on 12 sites dry matter contents were 23.8 and 23.0% respectively with N
applications of 39-52 and 130-169 kg/ha N. Similar results were obtained in
2 other series one with a single cultivar at 14 sites, the other on 6 sites with 3
cultivars. Again in Norway dry matter contents were 24.5% with 40 kg/ha N
and 23.6% with 120 kg/ha (Ekeberg, 1972). Dry matter content was affected35

to a smaller extent by nitrogen applied in addition to farmyard manure in the
Aspach long-term experiment, as shown in Table 29 (Lou6, 1977).
4.2.1.2 Effect of phosphorus
Effects reported are slight and variable. Hahlin and Johansson (1973) foundthat P slightly increased D.M. content in 64 experiments (20.0, 20.1 and20.2% with 0.92 and 183 kg/ha P205); Furunes (1975) found no effect in 46
trials, while Ekeberg (1972) in 9 experiments found that applying 108 kg/ha
P205 compared with nil reduced dry matter content from 24.2 to 24.0%.
4.2.1.3 Effect of potassium
Applying potash usually reduces tuber dry matter content but the effect isoften less marked than is that of nitrogen. Because the number of results isvery large we again confine ourselves to mentioning only the more
important. Much work has been done on this problem in Norway and of this,Table 30 is an example (Furunes, 1975). Mean dry matter contents in 9 otherexperiments (Ekeberg, 1972) were 24.2, 24.0 and 23.9% at 0, 75 and 148
kg/ha K20 and in another series (Ekeberg and Ronson, 1973) with 5
cultivars they were 24.7, 24.5 and 24.2% at 0, 84 and 169 kg/ha K20. In
Denmark, Hojmark obtained the results shown in Figure 10. In thisexperiment the effect of K2 SO 4 was less pronounced than that of KCI
particularly at high K20 rates. In the long-term experiment at Aspach (Lou6,
1977) mean dry matter contents over 17 years were 22.9, 22.4 and 21.8 forapplications of 0, 100 and 200 kg/ha K20 in addition to farmyard manure.
Table 28. Effect of nitrogen rate on dry matter content of tubers (average of
46 experiments)
Dry matter content
kg N/ha
23.4%
0
22.9%
60
22.4%
120
Table 29. Effect of increasing nitrogen rate on dry matter content of tubers(average of 17 annual results)
kg N/ha
50
100
150

36

Dry matter in tubers
22.49%
22.39%
22.19%

Table 30. Effect of potash on dry matter content of tubers (average of 46
experiments)kg K20/ha

Dry matter content
23.2%
22.9%
22.7%

0
120
241

Dry matter
content (%)
Bintje (13expts.1

Satuma (11expts.)

K2SO4

25 24 -S
23 -

KCI

22-

K2SO 4

2

-

0

KCI
108

217

325

,.glC
0

2O/ha

108

217

325

Fig. 10. Mean effect of rate and form of potash on dry matter content oftubers in 2 series of experiments.
Prummel (1981)
ments:

obtained the following dry matter contents in 43 experi-

kg/ha K20

Autumn application

Spring application

0
150
300

22.4%
22.1%
21.9%

22.4%
21.8%
21.4%

In 4 earlier experiments, he found no diminution from 100 or 200 kg/ha K 20
though it fell by 0.8% when 400 kg was applied (Prummel, 1973). Temme(1970a) reports that dry matter content was increased to a variable extent
when up to 200 kg/ha K20 was applied in 4 out of 7 trials, while it was reduced in the other three. Alblas (1973) also in the Netherlands found that dry
matter content decreased as leaf K content and soil K content increased.

37

4.2.1.3.1 Effect ofform of potash
Using sulphate of potash usually gives a higher dry matter content thanmuriate. A summary of the main results available is given in Table 31. The
effect of S04 as against Cl is usually more marked at high rates ofapplication.
4.2.1.4 Effect of magnesium
Putz et al. (1976) in West Germany found that applying 42 kg/ha MgO did
not affect dry matter content but in Finnish experiments (Varis, 1972c)
increasing magnesium (0, 60 and 120 kg/ha MgO) reduced it slightly (20.0,
19.5 and 19.8% respectively).
4.2.2 Starch content
Generally speaking, starch content moves hand-in-hand with dry matter content. K6ster and Ohms (1979a) advise that optimum starch contents are 13.5
to 14.5% for table potatoes and 16.0% for potatoes for crisps. Usually starchcontent is much more determined by variety than by fertilization.
4.2.2.1 Effect of nitrogen
Several workers have found that moderate rates of nitrogen enhance starchcontent while heavier rates depress it. An example is in the following figuresfrom Polish experiments over 3 years (Ciecko and Mazur, 1974):
No
N 60

13.6%
14.0%

N 120

13.4%

N 180

13.4%

N 240

12.8%

In another series (Ciecko, 1974a) N had no effect up to 150 kg/ha but
depressed starch content at 250 kg/ha. Mdller (1977b) in pot experiments
found an increase from 0.75 to 3 g N per pot and a decrease at 6 g/pot.
Acc6rding to Munzert (1982) N had no effect on a site with high N reserves
while it decreased starch content at another site. Black and White (1973) in
Canada found that N applied at up to 151 kg/ha had no effect. Kushizaki(1975) found no effect at 40 kg/ha N and a decline at higher rates of N.

38

Table 31. Effect of form of potash on dry matter content of tubers
Rate of K20(kg/ha)
181
542
108
217
325

108
217
325
224
120
246
370
200-230
232

KCI

K2SO4

Difference

20.1
18.6
21.8
21.1
20.3
24.5
23.7
23.3

20.7
20.0
22.5
22.0
21.9
25.0
24.5
24.2

No. of experiments
or annual results
64

Reference

22.48
21.68
20.88
20.7

22.48
22.89
21.73
21.2

0.6
1.4
0.7
0.9
1.6
0.5
0.8
0.9
0.5
0
1.21
0.85
0.5

Hahlin and Johansson (1973)

21.9

22.6

0.7

3

Sharma et al. (1976)

18.48

19.18

0.7

2

Cooperativa Agricola de Cotia (1980b and c)

13

Hojmark (1977)

11

Hojmark (1977)

10
3

Putz et al. (1976)
Lou6 (1977)

Temme (1970b)

Although numerous cases are reported of reduction of starch content by N
application, only the most important observations are discussed here. Resultsof Swedish experiments (Svensson et al., 1973) are given in Figure II
showing clearly that increasing N reduces starch content while Table 32
quotes results obtained by Hunnius et al. (1971) in West Germany wherestarch content was reduced by 0.3 to 0.4% according to variety. Hunnius andMunzert (1979) found values of 15.9, 15.7 and 15.5% starch content at 80,
120 and 160 kg/ha N (average of 3 cultivars for 3 years on 4 sites). T~ihtinen(1978) in Finland observed that increasing N from 50 to 150 kg/ha reduced
starch content from 17.9 to 16.8%.

Starch content (%)
2019
18
17H
kg N/ha

0

75

150

225

300

Fig. 11. Effect of increasing N fertilizer on starch content of tubers (averageof 18 experiments).
Table 32. Mean effect of nitrogen rate on starch content in 4 cultivars
Cultivar
Feldeslohn
lrmgardLori
Ddsir~e40

kg N/ha
60
15.1%
15.6%
16.1%
15.2%

No. of annual results
120
14.7%
15.3%
15.8%
14.9%

17
17
17
12

4.2.2.2 Effect of phosphorus
Solle (1980) in West Germany found that applying 120 kg/ha P20 5 asagainst nil increased starch content from 11.9 to 12.8% (4 year means).
Kushizaki (1980) in Japan mentions that in 3 experiments starch content
increased from 13.2% with no phosphate to 13.3, 13.5 and 13.8%,
respectively with 50, 100 and 150 kg/ha P205. Varis (1972a) and Ciecko(1974a) also found that P fertilizer positively affected starch content. Lou6
(1977), on the other hand, in one experiment obtained no effect.
4.2.2.3 Effect of potassium
More often than not, increasing dressings of potash reduce starch content
though it should be pointed out that in some cases the effect is only veryslight or non-existent at moderate rates of dressing. K can reduce starchcontent through an increased water content in the tubers although potassium
activates enzymes involved in starch formation (Forster, 1981). For example,
in East Germany (Brucholz et al., 1979), starch content was not affected by
72 kg/ha K 20 but was decreased by 0.2 and 0.6% with 144 and 216 kg/ha
K20. In 8 other experiments they reported that starch content declined from
13.7% at 72 kg/ha to 13.5 and 13.2% at 144 and 216 kg/ha K20.
Essentially similar results to the above have been reported by: Kushizaki(1975) - no effect or a slight diminution when the rate of K 20 reached 150
kg/ha; Rinno et aL (1973) (11 experiments in East Germany) - 16.3% in theabsence of K fertilizer and reductions of 0.6, 1.1 and 1.6% by 80, 160 and
320 kg/ha K20; Ti.htinen (1978) (14 experiements in Finland) no effect from50 to 100 kg/ha K20, but 0.3% reduction from 50 to 200. Other similarreports are by Black and White (1973), Varis (1972 a and c), Ciecko (1974a), Lou6 (1977), Gajek (1971) and Mirswa et al. (1981).
Figure 12 shows results from an irrigation trial with varying rates of K fertilizer in Poland (Nowicka, 1980): contrary to the behaviour in the dry crop increasing potash increased starch content of the irrigated crop except at 270
kg/ha K20.
Several reports are available of positive effects of potassium on starch content: Shukla and Singh (1976 a) (India) an increase of 0.35% by increasing K
application from 60 to 180 kg/ha K20; Siebold (1971) (West Germany) amarked increase of + 1.7 and + 2.3% from heavy dressings of 300 and 600
kg/ha K20 on a strongly K fixing soil; Graf Ballestrem (1977) (Kenya);Mengel (1969) increases of 0.4, 0.6 and 0.7% by applying 120, 160 and 200
kg/ha K20 (average of 89 trials). According to Prummel (1981) starchcontent was increased by K 2S04 (30-300 kg/ha K20) on a soil low in K, the41Starch content (%J12 [without irrigation

11[

with irrigation
90

0

180

270

L,kK 2O/ha

Fig. 12. Effect of irrigation and potash on tuber starch content (average of 3
annual results).
highest starch content being obtained with 90 kg/ha K20. In anotherexperiment, starch content was clearly higher with K2SO4 than with KCI(Figure 13). Kushizaki (1975) observed no effect of K on starch content.
Ktster and Ohms (1979 a and b) related starch content of tubers grown on
different soils to soil and tuber K contents, the relation was negative in bothcases. Less negative relations are reported by Munzert et al. (1982).

Starch content (%)

K2SO4-Spring appi.

17

KCI-Autumnappl.

.

16
15
141I

I

I

I

0 50100150

KCI-Spring appl.

- kg/haK20

300

Fig. 13. Effect of potash form and time of application on starch content oftubers.

42

Table 33. Effect of form of potash on starch content of tubers
Rate

KCI

K 2SO4

Difference

12.9

13.9

13.0

13.67
16.9

1.0
0.3
0.67
0.4

16.16

-0.23

of K 20232

Reference

annual results(kg/ha)
151
224
180

No. ofexperiments or

16.5
16.39

24
10
6

Varis (1970)
Pulzetal. (1976)
Bruchholzetal. (1979)

3
2

Shama etal. (1976)
Cooperativa Agricolade Cotia (I 980b and c)

4.2.2.3.1 Effect ofform ofpotash
The mean effects from many trials are given in Table 33, from which it isseen that normally sulphate gives a higher starch content than muriate. Other
authors reporting a positive effect of K2504 compared with KCI are
Achmedov and Vyalko (1971), Garin (1979) and Prummel (1981).
Ivanov and Boradich (1972) observed no such effects while the same isreported by Bruchholz (1976). Working with nutrient solutions, Header(1976) showed that the effect of SO4 in increasing starch content was mainly

due to improved translocation of metabolites to the tubers, thus, 24 hours
after applying 14CO2, 21% of the assimilated label was found in Cl tubers
compared with 39% in S04 tubers.
4.2.2.4 Effect of magnesium
Varis (1972 c) from Finland found slight reductions in starch content byapplying magnesium - 15.0% at 0, 14 and 60 or 120 kg/ha MgO. Hunnius etal. (1977) concluded from 29 experiments, that the effect of magnesium
varied according to site, and Beck (1975) found that Mg had no effect on
second early and late maincrop cultivars but that it reduced starch in very latemaincrop cultivars.
4.2.3 Specific gravity of tubers
Specific gravity of potatoes is often taken as an indication of dry matter content (and/or starch content), frequently authors describing fertilizer effects on
quality confine themselves to quoting specific gravity values. In Canada,
Dubetz and Bole (1975) found that increasing nirogen in pot experiments
reduced specific gravity as was also found in the USA by Kunkel et al.
(1973). White et al- (1974) in Canada on the other hand concluded that43

increasing N application from 90 to 134 and 180 kg/ha increased specificgravity from 1.094 to 1.095 and 1.096.
In the same pot experiments, Dubetz and Bole (loc. cit.) found that
phosphorus increased specific gravity.
Potash fertilizer reduces specific gravity but the reduction is less when
K2SO4 is substituted for KCI. Thus McDole et al (1978) in the USA givevalues (mean of 4 cultivars) of 1.085 without K fertilizer and of 1.079 and1.080 for potatoes receiving 280 kg/ha K20 as KCI and K2 SO 4 respectively.
White et al. (1974) and Kunkel et al. (1973) also found that K fertilizer
reduced specific gravity. Rowberry and Ketcheson (1978) applied 152 kg/ha
K2 0 by placement both as KCI and K2SO4 and obtained the following
values (mean of 4 years): no potash 1.084; KCI 1.082 and K2SO4 1.085.
Two trials in Brazil (Cooperativa Agricola de Cotia, 1980b and c) gave
values of 1.053 and 1.065 with 232 kg/ha K20 as KCI and K2SO4
respectively.
4.2.4 Protein content
The amino-acid composition of potato protein and the relatively high content
of essential amino-acids confers a biological value of the same order as thatof animal protein (Mbller, 1973).
4.2.4.1 Effect of nitrogen
Protein content, usually expressed as a percentage of dry matter, is very
favourably affected by nitrogen fertilizer. Ziinker et al (1975).in East Germany found crude protein contents (% of dry matter) of 8.14 and 9.66 at 60
and 240 kg/ha N (experiments at 6 sites over 3 years). Somorowska and
Kakowska-Lipinka (1972) in 15 experiments in Poland obtained protein contents in fresh material of 1.68, 2.15 and 2.29% at 0, 120 and 180 kg/ha N.
Similar results have been reported by Wilcox and Hoff (1970), Mica (1971),
Enge and Baerug (1971), Jiirgens (1971), Westerlind (1974) cited by
Aakeberg (1975), Rinno and Richter (1975), Rexon (1976) and Rinno et al.
(1976). Mica (1971) and Wilcox and Hoff (1970) found that N fertilizer
increased true protein.
In a pot experiment, Eppendorfer (1978) found that increasing N fertilizer
improved crude protein digestibility.
Some workers have studied the effect of N fertilizer on the nutritional valueof potato protein expressed by the essential amino-acids index (EAAI).
Baerug et al. (1979) (6 sites, 3 cultivars, 3 years) obtained values for thisindex of 64, 64 and 62 at 50, 100 and 150 kg/ha N. Rexen (1976) examined44the effects on 33 cultivars over I or 2 seasons in Denmark applying approx.
110 kg/ha N compared with approx. 180 and found that EAAI was reduced
by increasing N in many cultivars and not affected or slightly raised inothers. Winsch and Hunnius (1980) applied 0.5 and 5 g N per pot in a pot
experiment and observed that increasing N had no effect on EAAI in 3
cultivars but reduced it slightly in a fourth. Eppendorfer (1978) reporting on
another pot experiment found that increasing N reduced EAAI.
4.2.4.2 Effect of phosphorus
Mica (1971) in Czechoslovakia, found that increasing P205 application from44 to 220 kg/ha reduced crude protein in the fresh matter from 1.64 to 1.30%
with a similar effect on true protein.
4.2.4.3 Effect of potassium
Results reported are somewhat contradictory. Shukla and Singh (1976b) in
India reports a positive effect of K with crude protein contents of 10.64,
10.98 and 11.28% of d.m. at 60, 120 and 180 kg/ha K20. Nowicka (1980) in
Poland found that potash increased protein content in the absence of
irrigation but had no great effect when the crop was irrigated (Figure 14).
According to Enge and Baerug (1971) in Norway there was no effect on
crude protein in 3 varieties when they increased the potash dressing from 50
to 150 kg/ha while Mica (1971) found a reduction in crude and true protein
contents of fresh material when potash was increased, the values were 1.42
and 1.30% at 58 and 289 kg/ha K20.

Contents(%)
Total proteins

10

without irrigation...
with irrigation
Digestible proteins-- - - - -

0

90

I
180

rf I
270

r
0

I
90

,
180

r
270

t kg K40/ha

Fig. 14. Effect of potash on tuber protein content (mean of 2 annual results).

45

Varis (1973 b) reports that K2SO4 compared with KCI increased tuber protein content in two cultivars, the mean value (% of fresh material) being
1.65% with K 2SO 4 and 1.49% with KC.
4.2.5 Reducing sugar content

According to Stricker (1971) reducing sugar content (glucose + fructose) ofpotatoes for crisps should not exceed 0.25% and of those for chips and dehydration it should not exceed 0.5%.
Rinno et a. (1972) in East Germany in 5 trials found reducing sugar contentsof 0.37, 0.43 and 0.49% at 0, 40 and 80 kg/ha N but the content did not risewith further increase of N up to 160 kg/ha (0.43 and 0.46% respectively at
120 and 160 kg/ha) Kamal et al. (1974 b) observed that N fertilizer increased
reducing sugar content, while Muller (1977) found no effect in pot experiments.
Kamal et al. (ibid.) mention that P fertilizer increased the reducing sugar
content.
3 East German experiments reported by Rinno et al. (1972) showed that increasing K fertilizer tended to reduce the reducing sugar content (0.46, 0.37
and 0.42% with 0, 160 and 320 kg/ha K20) but Kamal et al. (1974 b) foundthat K increased the content.
Stricker (1971) concluded that the form of potash (KCI and K2SO4) had noeffect on the reducing sugar contents of potatoes stored in different ways,
while in one experiment in Brasil (Cooperativa Agricola de Cotia, 1980 a, b,c) K2SO4 reduced the content, having no effect in two other trials.
4.2.6 Lipid content

Nowicka (1980) found that 180 kg/ha K20 applied with farmyard manure at
25 t/ha greatly increased the lipid content of potatoes (Table 34).
Table 34. Effect of potasium on lipid content of tubers (average of 2 years
results)kg K20/ha
0
90
180
270

46

Lipid content %Without irrigation
0.33
0.38
0.47
0.46

With irrigation
0.24
0.28
0.39
0.40

4.2.7 Fibre content
Nowicka (1980) found that increasing the potash dressing applied in addition
to farmyard manure, increased the fibre content of tubers, the effect being
less marked when irrigated (Table 35).
Table 35. Effect of potassium on fibre content of tubers (mean of 2 years
results)kg K20/ha
0
90
180
270

Fibre content %Without irrigation
1.91
2.47
2.45
2.57

With irrigation
2.00
2.09
2.17
2.19

4.2.8 Vitamin content
Miller (1977 b) observed that N applied in pot experiments had no effect onvitamin C content of potatoes. There are reports Ciecko, 1974 b; Ciecko and
Mazur, 1974 that N applied in experiments over 3 years reduced vitamin C.
A favourable effect of phosphorus on vitamin C content was noted by Ciecko(1974 b) and by Tashkodzaev (1975) cited by Smith (1977) while Klein etal. (1980) found that applying P increased the ascorbic acid content.
In two Indian experiments (Shukla and Singh, 1976 a) vitamin C levels were
20.4, 20.8 and 21.1 mg/100 g fresh material at rates of 60, 120 and 180 kg/ha
K20. Other favourable reports of the effect of potassium on vitamin C and/or
ascorbic acid contents are by Jundulas et al. (1975), Protashchik and Dmitrieva (1976) and by Sharma et al. (1976). In experiments over 3 years in
Poland (Ciecko, 1974 b) applying 50 kg/ha K20 increased vitamin C; 100kg/ha left it unaffected, while 150 and 300 kg/ha reduced it.
Sharma et al. (1976) from India report ascorbic acid contents of 20.0 and
19.0 mg/100 g fresh weight with K2SO 4 and KCI respectively.
4.2.9 Alkaloid content
Ahmed and Mfiller (1979) found that increasing the level of N fertilizer in
pot experiments had no appreciable effect on solanine content but reduced
the content of o-chaconine. The content of both was increased by applying
potash.

47

4.3 Cooking quality of tubers
4.3.1 Texture
The desirable texture of potatoes after cooking is very much a matter of personal preference and in any case depends on the method of cooking and the
purpose for which the potatoes are required. Some have a preference formealy mashed potatoes, while others who prefer a boiled potato which keeps
its shape would regard the former as undesirable because it readily disintegrates on boiling. In general, high dry matter, high starch potatoes tend to
give a mealier product after cooking. It should also be pointed out thatdifferences between cultivars are very much greater in respect of these
aspects of quality than are differences which may be induced by varying
fertilizer treatment.
Tllhtinen (1978) in 14 experiments and Varis (1972 b) observed that increasing nitrogen reduced mealiness while Enge and Baerug (1971) observed the
opposite. The effect of increasing nitrogen is to reduce the tendency to disintegration (fall) on boiling, as reported, for instance by Enge and Baerug(1971), Varis (1972 b), Kudelja and Wirsing (1976).
According to Hahlin and Johansson (1973) phosphate fertilizers made potatoes more likely to fall on boiling and increased dryness of the final product.
Varis (1972 b) found that phosphate application increased mealiness anddisintegration on boiling.
The effect of increasing potassium is usually to reduce dry matter and starchcontent (see 4.2.1.3 and 4.2.2.3) so that, where authors have commented on
effects of K fertilizer on texture it has usually been to the effect that
increasing K reduces disintegration on boiling and reduces mealiness while
giving a moister final product.
Table 36 (Hojmark, 1977) shows that increasing K reduced the tendency todisintegrate and that this effect was more pronounced with KCI than with
K2SO4 at high K20 rates. Disintegration on boiling was studied in 7 experiments by Bruchholz (1976) and the mean indices of disintegration were 1.54,
1.36 and 1.41 with 0, 120 and 240 kg/ha K20 (l=no disintegration, 4=complete disintegration). He also mentions 8 experiments where the index of disintegration was 1.54 with KCI and 1.72 with K2SO4. Hahlin and Johansson(1973) also mention that potassium reduced disintegration while substituting
K2SO4 for KCI had no effect. Enge and Bacrug (1971) report that potassium
reduced disintegration while Varis (1972 b) found no effect.
T~ihtinen (1978) in 14 experiments and Bruchholz (1976) in 7 experiments
observed that potassium reduced mealiness. The same is reported by Varis(1972 b) while Enge and Baerug (1971) found no effect on soils rich in48

potassium. K2SO4 produced a somewhat more mealy potato than KCI inseries of experiments reported by Varis (1970) (experiments over 4 years at
3 sites with 3 cv.) and by Bruchholz (1976) (8 experiments). According to

Hcjmark (ibid) and Hahlin and Johansson (1973), dryness of cooked tubers
was reduced by potassium, this effect being more pronounced with KCI thanwith K2SO4.

Table 36. Effect of rate and form of potash on tuber disintegration (averageof 3 experiments)kg K20/ha
0
90
180
270

Index of disintegrationKCI

K 2 SO4

2.1
1.3
0.2
0.2

2.1
1.3
1.1
0.7

4.3.2 Flavour

Flavour is a subjective matter and therefore difficult to describe in quantitative terms. The usual procedure is to submit samples to a tasting panel who
allot marks, but there must always be some doubt as to the reliability of
results since personal preferences are so variable.
The generality of results seems to indicate that increasing the nitrogen dressing adversely affects flavour to some, usually small, degree, e.g. Tfihtinen(1978), Enge and Baerug (1971), Jonsson and Johansson (1971), Varis(1972 b) but there are reports, e.g. Kudelja and Wirsing (1976) that it has noeffect.
Varis (1972 b) and Hahlin and Johansson (1973) mention that P fertilizer
somewhat improved flavour.
Tihtinen (1978) found no effect of potassium on flavour in 14 experiments.
Bruchholz (1976) mentions 7 experiments where the flavour index (1=very
good, 4=bad) was 2.11, 2.35 and 2.25 with 0, 120 and 240 kg/ha K20 and heobtained a slightly better flavour with K2SO4 than with KCI in 8
experiments. Rowberry and Ketcheson (1978) found no effect of potash or of
the form of potash. Varis (1972 b) and Hahlin and Johansson (1973) mention
an adverse effect of potassium on flavour. Varis (1970) observed that K2 SO4
improved flavour in comparison with KCI (experiments over 4 years at 3
sites with 2 cv.); this is also reported by Hahlin and Johansson (1973).

49

4.3.3 After-cooking blackening
This, which is usually more pronounced at the stem and end of the tuber andsometimes spreads throughout the flesh is due to the formation of a black
pigment which is an iron compound.
4.3.3.1 Effect of nitrogen
Berryman et al. (1973) from two series of 6 and 8 experiments in Englandfound that increasing N application had no effect and Tiihtinen (1978) inFinland found the same in 14 experiments. Polish workers (Rostropovicz andFotyma, 1978) found that N fertilizer increased after-cooking blackening andEnge and Baerug (1971), Varis (1972 b) and Holm (1978) came to the sameconclusion.
4.3.3.2 Effect of phosphorus
In England, Berryman et al. (loc. cit.) found no effect of P in 6 experiments
but in the other series of 8 trials P reduced blackening from 16% without P
fertilizer to 9 and 11% with 56 and 112 kg/ha K20. Hahlin and Johansson(1973) also found that P decreased the incidence while Varis (1972 b) foundno effect.
4.3.3.3 Effect of potassium
Reports of increasing K fertilizer decreasing blackening are given by: Berryman et al. (1973) (Table 37), though in another series they reported noeffect; Varis (1972 b); Hahlin and Johansson (1973); Protashchik andDmitrieva (1976); Holm (1978) and Mirswa et al (1981). Other authors:
Tiihtinen (1978), Hojmark (1977) and Bacrug and Enge (1974) observed noeffect of potassium on after-cooking blackening.

Table 37. Effect of potash on after-cooking blackening (% blackened tubers)
kg K20/ha
0
113
226

50

Means of6 experiments

8 experiments

18
16
14

13
13
10

4.3.3.1 Effect ofform of potash
Varis (1970), in Finland, found less tendency to after-cooking blackening in
K2SO 4 than in KC1 treated potatoes (blackening index 0.9 respectively 1.2)
in a series of experiments lasting 4 years with 2 cultivars on 3 different soil
types. Hojmark (1977) reports no effect in 13 experiments in Denmark but
Hahlig and Johansson (1973) report in favour of K2SO4.

4.3.4 Crisp colour
Crisps should not be too dark coloured. A high content of reducing sugars,
which react with amino acids to produce a dark pigment (see 4.2.5) is therefore undesirable. A striking example of the effect of potash fertilizer on crisp
colour is given in Table 38 from Hojmark (1977). Increasing K improved
colour and K2SO4 was more effective than KCI. Varis (1972 b) found that
nitrogen improved colour while phosphate and potash had no effect, whereas
Plate 3 shows an improvement of crisp colour under the effect of potash.

Table 38. Effect of rate and form of potash on crisp colour
Crispsmanufactured inKg K20/ha

Colour index*
Bintje (13 expts.)

Saturna (I I expts.)

KCI

K2SO4

KCI

K2SO4

August

0
108
217
315

5.7
6.6
6.9
7.3

5.7
5.9
6.4
6.9

7.3
8.1
8.2
8.5

7.3
7.6
7.6
7.8

December

0
108
217
315
0
108
217
315

4.7
6.2
6.8
7.6
4.7
5.7
6.2
6.8

4.7
5.3
6.2
6.3
4.7
5.1
5.6
5.7

6.7
7.9
8.4
8.8
6.7
7.4
8.0
8.0

6.7
7.3
7.9
8.4
6.7
7.0
7.5
7.3

February* Scored

1-10; l0=-light colour

514.4 Storage behaviour
Reports on the effect of N fertilizer on storage losses of potatoes indicate thatit tends to increase losses. One example from Schnieder (1972) is given in
Table 39. B6hmig et al. (1975) found in 2 experiments storage losses of 6.9,
Table 39. Effect of nitrogen on storage losses
kg N/haLosses (%)

0
40
80
120
160
200

8.7
8.4
9.2
9.9
10.3
10.4

9.4 and 10.9% at N levels of 0, 150 and 330 kg/ha. Negative effects are alsomentioned by Autorenkollektiv (1973) cited by Kudelja and Wirsing (1976).
Amberger (1968) found that potash fertilizer reduced storage losses, related
to reduction in the activity of catalase and peroxidase (Table 40). A positiveeffect of potassium is also reported by Mirswa et al. (1981).
Table 40. Effect of potash on dry matter losses in storagekg K20/ha

Dry matter loss

0
100
200

20.3%
5.6%
6.0%

Enzyme activity
Peroxidase
1.5
1.3
1.1

Catalase
13.2
5.6
6.0

4.5 Summary of effects of fertilizers on quality
We have attempted to summarize the effects described in this chapter inTable 41. The farmer's first consideration should be to apply fertilizers toincrease yield and hence his net profit and for this it will almost invariably
mean applying all the three nutrients N, P and K. If the fertilizers are correctly balanced, the result will normally be to improve overall quality. So far
as potash fertilizer is concerned, it is worth remarking that the use of sulphaterather than muriate of potash usually gives a higher quality tuber.

52

Table 41. General tendencies of effects of N, P and K and form of K on quality
Criterion

N

Proportion marketable tubers
Mechanical damage to tubers
Internal blackening
Dry matter content
Starch content
Protein content
Vitamin C content
Disintegration on cooking
Meatiness of cooked tubers
Dryness of cooked tubers
Flavour of cooked tubers+
Variable+O

K

Form of K(K2SO4-KCI)*

+

- (O)

Nil orvariable
+
+
+

+
+
+

Variable++0

Poorer++Improved by
K2SO4

After cooking blackening
Crisp colour

0 (+)

Storage losses
Specific gravity of tubers++ increase
O no effectP

Nil orpoorer0-

0 (-)
Improved

Poorer with
K2SO4+

- decrease* Difference between values with K2 SO4 and KCI

5. Effects of fertilizers on plant healthIn general, it is true to say that balanced fertilizer applied in the correct
amount improves plant health and hardiness, in some cases by making infection by pest or disease less likely and in all cases because the improved
vigour conferred on the plant by adequate nutrition enables it to recover
more quickly from the effects of pest, disease or other adverse circumstance.
5.1 Fungal diseases- Late blight (Phytophthora infestans)
Some interesting results by Btihming et al. (1975) in East Germany arequoted in Table 42; the figures indicate seasonal variation in the effect of N.
Varis (1972 b) found that tuber blight was slightly increased by N fertilizer
and unaffected by phosphorus and potassium. Szcotka et al. (1973) found in
solution culture that increasing K in the solution from 25 to 150 ppm reduced53leaf resistance while further increase to 400 ppm increased it, there being nodifference between KCI and K 2 S04 . Herlihy (1970) found that resistance toblight was reduced by N fertilizer and increased by phosphate.
Table 42. Effect of nitrogen on % leaves affected by late blight (mean of 2
cvs. on 6 sites)
Year
1970
1971
1972

Kg N/ha
0
25.1%
19.2%
5.0%

60
25.5%
19.7%
5.5%

150
42.7%
11.9%
4.8%

240
26.0%
10.5%
2.4%

330
21.9%
7.5%
1.2%

- Powdery scab (Spongospora subterranea)
Wenzl and Reichard (1974) studied in 1963 the effects of nitrogen,phosphate (basic slag) and potash in a long-term experiment begun in 1959.
They found the disease to be favoured by nitrogen, reduced by phosphateand slightly reduced by applying 225 kg/ha K20. Liming reduced thepercentage of disease-affected tubers in many experiments in Austria (Wenzl
et al., 1972).
- Rhizoctonia (R. solani)

Varis (1972 b) found the percentage tubers affected to be increased by both
nitrogen and potassium and decreased by phosphorus, but B6hmig (1975)
found that increasing nitrogen reduced the attack.
- Dry rot of potato (Fusarium coeruleum)
Langerfeld (1973) inoculated tubers from plots which had been under thesame fertilizer treatments for ten years and found that the condition was
favoured by nitrogen and potassium but unaffected by phosphorus (Table
43).
- Verticillium wilt (V. albo-atrurn and V. dahliae)
O'Sullivan and Reyes (1980) found that this was not affected by N fertilizer.
Table 43.
Fusarium

Effect of nitrogen, phosphate and potash on development of
Severity index

Treatment (kg/ha)
N
0

P205
100

K20
200

2.70

80
80
80

0
100
100

200
0
200

3.74
2.62
3.78

54

5.2 Bacterial diseases- Common scab (Streptornyces scabies)
The evidence appears contradictory. Wenzl and Richard (1974) found that intheir long-term experiment started in 1959 nitrogen slightly increased scabby
tubers in 1963 and appreciably increased it in 1970. While B6hmig et al.
(1975) report that nitrogen had no effect, Varis (1972 b) found that nitrogen
reduced the severity.
In the long-term experiment mentioned above, Wenzl and Richard observedthat basic slag favoured scab in 1963 and 1970 (more severely in 1970) but
in another experiment begun earlier they found that while hyperphosphateincreased it a little and basic slag increased it markedly, superphosphate had
no real effect; the differences can be ascribed to effects on soil pH (Table 44)(Wenzl et al., 1972). Davis et al. (1976) mention that triple super-phosphate
greatly reduced scab, for instance in one experiment the percentage of tubers
having more than 10% of their surfaces affected was 26% and 11% without
and with 168 kg/ha P205. Varis (1972 b) also found that phosphate reduced
scab. Wenzl and Richard (1974) obtained no effect of potassium in 1963 and1970. in their long-term experiment and Varis (1972) reported similarly
though Davis et al. (1976) found that potash appreciably increased scab.
Liming increased scab in several experiments reported by Wenzi et al.
(1972).

Table 44. Effect of form of phosphate on soil pH and scab incidence
kg P20 5/ha
0
100
100
100

Form of P fertilizer
Superphosphate
Hyperphosphate
Basic slag

pH (KCI)
5.05
5.15
5.22
5.62

Scab index
2.9
3.1
3.7
5.0

- Blackleg (Erwinia carotovora)
As shown in Table 45, B6hmig et al. (1975) found that increasing nitrogen
reduced the number of affected plants.
- Brown rot (Pseudomonas solanacearuin)
Mahmoud et al. (1976) in two pot experiments observed that brown rot wasmuch reduced by nitrogen and phosphate but unaffected by potash.

55

Table 45. Effect of nitrogen on blackleg incidence - no. affected plants perplot (mean of 2 cvs. on 6 sites)
Year
1970
1971
1972

kg N/ha
0
1.92
4.57
4.84

60
1.39
4.08
4.13

150
0.86
3.47
2.92

240
0.76
3.20
1.63

330
0.56
3.41
1.08

5.3 Virus diseases
On the evidence of field experiments in the Netherlands, Schepers andBeemster (1976) came to the conclusion that there is no reason to supposethat normal applications of nitrogen, phosphorus and potassium as applied toobtain optimum yield would have any adverse effect on the rate of virus
infection of seed tubers. In Portugal, Quelhas dos Santos (1979) reports on
an experiment in which, one month after emergence, plants on the NP treatment were severely affected by leaf-roll while those on the NPK plots werenormal; the eventual yields were respectively 11.23 and 27.85 t/ha.
5.4 Physiological disorders
Nelson (1970) found in the USA that applying potash on a soil high in potassium reduced the percentage of hollow hearts (Table 46), the effect being
particularly evident in 1965 when incidence of the condition was high.
Table 46. Effect of potassium on % tubers with hollow hearts
kg K20/ha
0
74

Year
1965
26.0
15.9

3 year mean
1966
17.3
14.7

1967
2.4
1.5

11.4
8.0

5.5 Cold
In an Indian experiment, Saini (1978) found that frost damage to leaves was
16% and 20% at 0 and 200 kg/ha N and 19 and 17% at 0 and 200 kg/ha
P205, while applying 200 kg/ha K20 reduced frost damage from 38 to 7%.
In 14 experiments in India, Grewal and Singh (1980) found a negative
correlation (r= -0.89) on plots receiving no K fertilizer between available soil

56

K and frost damage to leaves. The index (no damage=0, 100% damage=4)varied between 1.1 and 3.2 at soil K below 114 mg/kg and between 0.4 and
0.6 at soil K above 124 mg/kg. Applying potash greatly reduced the damage(Figure 15). Jackson et aL (1982) also report that K made leaves moreresistant to frost.
Damage index on leaves
3.2

Okg K20/ha
3- 22100kg K20/ha
IO

2.1

2

1.0

1.8

1.9

1.5

1.3
I,

i

i2

o

0.4

4

5

6

. 02

02

0.4

00

1

0.6

U
04

2

(56) (78)3(85)

1921 (06)

7

0.2

0.4

0,4

0.

8

9

(08) [105) (1081(114)10

11

Soil No.

0

12

13

14

1124) (126) (1361 (140) 11581(Available K content, ppm)

Fig. 15. Effect of potassium on frost hardiness of potato leaves.

6. Method and timing of applying fertilizers
6.1 Method
Hojmark's (1976) results obtained in Denmark are quoted in Table 47. Placement had a beneficial effect as compared with broadcasting a compound fertilizer at low and medium rates of application but not at high rates. The sameauthor (1972) found placement of NPK more effective in 9 out of 15
experiments.
In the USA Dunton (1971) found no advantage from placement when 10-1010 fertilizer was applied at 1124 and 1686 kg/ha; the results for two cultivars
at 1124 kg/ha are quoted in Table 48.

57

Table 47. Effect of method of application of a compound fertilizer on yield(mean of 4 sites over 3 years)
Rate of 14-4-17(kg/ha)
357
714
1071

Tuber yield (t/ha)
Placement
Broadcast
9.0
15.9
19.1

12.2
17.7
19.3

Yield increase
due to placement (%)
36%
11%
1%

Table 48. Effect of method of application of compound fertilizer (10:10:10)
on yield
Application method

Placement
Broadcast after ploughing* and worked in
Broadcast just before ploughing
Broadcast in January

Yield (tlha) mean of 3 annual results
Cv. Superior
Cv. Pungo
15.27
26.20
15.61
24.61
16.45
26.82
17.32
27.37

* Ploughing was at the end of February or beginning of March

Favourable effects of placement of N are reported by Grewal et al. (1979); of
phosphorus placed in the furrow as compared with broadcast or banded byVerma and Grewal (1978) and of potash by the same authors in 1979.
Advantages in favour of placing NPK have been reported from Finland by
Varis and Lanetta (1974) and from France by Crosnier (1973) citing I.T.P.
(1970), but, as Crosnier says, fertilizer should not come into direct contact
with the seed tubers as there may be some phytotoxicity.
6.2 Timing of application
6.2.1 Nitrogen
Table 49 quotes W. German work (Hunnius and Munzert, 1979) and showsthat on brown earth soils applying part of the N dressing at the stage whenleaf cover was complete was disadvantageous, though the same workers

58found that on a sandy soil with 3 varieties over 3 years yield was increased
from 32.6 to 34.2 t/ha N was applied in split dressings. Table 50 gives resultsfrom Sweden (Svensson et al., 1973) showing no benefit from splitting orlate application. Loud (1977) in a long-term experiment at Ablis compared
applying 160 kg/ha N either as one dose or two applications of 80 kg/ha in
April and May; the latter treatment reduced yield by two t/ha from 32.9 tlha.
Gunasena and Harris (1979) in England obtained results on a sandy soil inagreement with those of Hunnius and Munzert (1979) on the sandy soil;
splitting a 220 kg/ha N dressing increased the yield of the early cultivar
Craig's Royal by 21% and of the maincrop Pentland Dell by 11%; in these
Table 49. Effect on yield of splitting nitrogen application (mean of 36
annual results)
Yield (tlha)
48.9
47.5
49.4
48.4

kg N/ha120
80 + 40160
80 + 80

Application
SingleSplit
SingleSplit

Table 50. Effect on yield of splitting and timing of nitrogen applications(mean of 18 experiments)
Before4 weeks after

planting

planting

Dose of N (kg/ha)
10 weeks
after planting

150
75
75
225
150
150

-

-

150

-

-

75

-

-

75
-

-

15 August

75

-

-

75

-

-

Yield (/ha)
33.7
32.5
32.5
33.7
34.0
33.4
33.1

experiments there was an advantage (22% for the early and 12% for the
maincrop) in applying all the fertilizer N late. Grewal et al. (1979) in India
found an advantage in splitting a dressing of 120 kg/ha N but no such effectat lower rates of 40 and 80 kg/ha.

59

6.2.2 Potassium
In England, on a sandy soil, (Anon., 1977) emergence of potatoes wasdelayed when KCI was applied a few days before planting but not when it
was applied 6 to 8 weeks before planting. Results in another experiment(Palmer and Stevens, 1980) averaged over 3 years showed that it waspreferable to apply a part or even the whole of the potash dressing either inautumn or at least 6 weeks before planting (Table 51) and it is suggested thatin dry springs potash applied at planting is less easily available. Further,
applying 600 kg/ha K20 as KCI at planting retarded early growth of the crop
though it had no marked retarding effect if applied in autumn or 6 to 8 weeks
before planting. Gunasena and Harris (1971) found that splitting the potash
dressing of 220 kg/ha K20 improved the yield of an early cultivar (Craig's
Royal) by 14% though it had little effect on the maincrop Pentland Dell.
Yield of both cultivars was improved by 5% when K was applied late rather
than early. According to Prummel (1981), yields were slightly higher with
autumn than with winter application of KCI in 43 experiments (50.1 and50.8 t/ha with 150 and 300 kg/ha K20 applied in autumn and 49.9 and 50.4
t/ha with 150 and 300 kg/ha K20 applied in winter). Temme (1970b)
observed that applying 200-230 kg/ha K20 as KCI in the autumn gave ayield of 46.8 t/ha compared with 44.6 t/ha when the potash was applied atplanting.
Table 51. Effect of time of application of potash on yield (i/ha) - mean of 3
annual results
Time of application
Autumn
6-8 weeks before planting
At planting
Split*kg K20ha
200
0
25.0
31.0
24.5
31.8
23.4
29.7
23.1
31.2

400
33.2
33.5
30.4
34.3

600
34.8
34.5
31.5
35.6

* 100 kg K20/ha at planting, remainder in previous autumn

Soni et al. (1980) also found splitting the potash dressing to be favourable
while Mazur and Ciecko (1979) found no difference between applying thepotash (either KCI or K2SO4) either before autumn cultivation or in spring
before planting.
Several workers recommend applying KCI several weeks before planting orin the preceding autumn to allow time for the leaching of chloride.

60

7.

Nutrient Deficiencies

7.1. Deficiency symptomsa)Numogeu
Initially pale green co]ouration of leaf margins and tips., the foliage
eventually turns pale vellor. Grovth is reduced and leaf-fall premature(Loud. 1977: Grewal, 1975; Gruner, 1963.
bi Phosphorus
Growth is retarded particulariy in the earl sIages Foliage dark green and insevere cases the lower Icaves turn pI rple ILeaIlCts d not (levCop nolrally(Loud, 1977: Grcwal, 19751c) Pota..ilxm
Internodes shortened: leaves bluishg-ree n in Colour. later older ICaeC's turnyellow with brown margins and apices Later necrotic batches appear ilou&.
1977; Grewal, 1975; Gruner. 1963) (Plates 4 and 5).
; Magne iiu
Lower Ieakes more li1hl colored than normal, first on tile
tips anId margin,of leaflets and then extending betwseen the veins with. later. necrotic patches
between the veins (loud, 1977: Gruner, 1963).
7.2. Varietal differences
Ekeberg and Ron sen ( 1973) in Norway showed that cult i ars differec ereatky
in susceplibility to K deficiency (lable 52).
Table 52.

Severity tfK deficiency sy mp in]s, In varioLs cutivars

CutivarKerrs Pink
Pimpernel
King George V
Ora
Parnassia
0 = no synplolls

kg K2O/ha
0
4.l1
3.5
2.)
2()
15

84
2.5
2,0
10
1.0
I0

01

Plate I The potato is one ol the most K-demanding crops: hence large yieldc n hc ex pected Ic ft:NP without polas]h. middle:
respomses to po)tassit
NP+140 kg K20/ha, tiht: NP+266 k, K()/ha).

b)
if hers can bejlj:ate 2 Internal hackening 0ug,,ret 1edLIced by applyiIng pt"ah especially

Plate 3 An example of the
improvcment ol crisp colouron owmK soils.

h) potassium applicatlon.

a) left: NP. iight: NP+K as muriale oI potash The crsps made lrotn
Potatoes Which receivedtKCI)
II left: NP, right: NP+K as sulphate of p tash potash (aboe) are
brig3ht golden bio n(K2S0 462

Plate 4. Reduced growth, reduced flowering and bish-green toliage are thefirst visible symptoms of potassium deliciency.

Plate 5. With increasing potash deficiency, internodes are shortened, leac,bend dow nward and Iurn ee lo, and later necrotic patches appear.

S.

World fertilizer practice

8.1.

Recommendations

A sttlIuiiary of reontton(eidatioll has been altilpted in Appendix 4. tliese
recommendations \arj gratd, accordiun to soI t \ pe. o Inutrtal siMit tI
whether r not farmy ard llanure is available. availability of irrigation nIIdthe
purpose for which the potatoes are intended
In countries where the a ragc national yield exceeds 25 ta, te N andfor portaoes lot hunin constJmption ai generall>P2(h ras rto llonlied
between 100 and 160 kg/ha. The potash rates recoinmended arc usuallyg/haItglhe. tile) generally exceed 200 kg/ha K20 and can go up to H0(MKj0. In countries ith avera tcvie ds losmes than 2) t/h;. the reconmmndediates of rlitrogeu and phosphorus teld to be lower In several ol thesecountits. the reomniuiended frtilizalion is unbalanced. For example. inlheranes of
mOtrast"twhat is observed in countries otaining high si
K 2) recimmmended are lover than those of N and P 20 8.2. Fertilizer practiceor N P and K iued in practice
Apenlx 5 sho s a% rage rates O
Table 53 shows that the dressings of nitrogeni, phosphtorus and especiallypotassi umi are arge in coilries where vie Ms exceed 25 t/ha and tile clrrespondin N:K ratio is 1:1.34. In countries with yield intrior to 20 tlha. thefertilizer rates are lower an din particular less potassium that) nitro.cn isappled (N:K ratio: 10.79).

[ablc 53 A verage N. 10(); and K20 itcs applied In cotiuntries with vields
higher than 25 t/ha or lower than 20 rlha (calculatd from Appendix 5)

Yield

that

> 25 t/ha< 20 i/ha

NO cortlfries
5
13

Average rae alPld
P205
N
116
31
87
112

I/ha)
K20
175
88

T'hcse igurcs show thit increased crop productin needs higher
dressings sinOe higher ehls lei ose iimor NIPK.

64.

errtilizer

9.

Appendices

Appendix 1. Mean effect of nitrogen on yield
Country (No. of
annual results)

kg N/haYield(t/ha)

Yield increase% kg tubers/
kg N

Reference

EuropeE. Germany (36)England (26)England (16)England (16)

Ireland (19)

Norway (46)

Poland (600)
Poland (15 = 3
sites x 5 cvs.)

0
60
150
240
330
0
75
150
225
0
126
188
0
75
150
225
0
45
90
135
0
60
120
0
120

34.9
41.4
48.4
52.2
52.6
26.9
33.5
36.1
36.8
32.6
40.4
42.1
34.20
39.87
42.46
42.73
38.7
43.2
45.2
47.2
21.73
26.91
28.50
22.8
30.4

0
60
120
180

33.9
37.4
37-2
34.8

Gerdes et al. (1975)
19
39
50
51

108
90
72
54

25
34
37

88
61
44

24
29

62
51

17
24
25

76
55
38

12
17
23

IO
72
65

24
31

86
56

33

63

i0
10
3

58
28
5

Webber et al.(1976)

Archer et al (1976)

Farrar and Boyd(1976)

Gately (1971)

Furunes (1975)

Roztropowicz andFotyma (1978)
Somorowska and
Kakowska-Lipinska(1972)

65

Country (No.
of annual
results)

kg N/haYield(t/ha)

Sweden (18)

0
75
150
225
300

28.3
32.0
33.7
33.7
33.1

0
60
120
180
0
112

26.0
32.4
34.6
33.0
15.43
20.60

Asia
Cyprus (17)India (35)

Lebanon (25)Syria (12)Turkey (28)

Yield increase% kg tubers/
kg N
13
19
19
17

49
36
24
16

25
33
27

107
72
39

34

46
34

0
60
0
80
0
80

14
101

Reference

Svensson et al.
(1973)

Krentos and Orphanos (1979)

Raheja (1966) in:
Raychaudhuri(1976)
CEA-IPI-ISMA(1974)
CEA-IPI-ISMA(1974)
CEA-IPI-ISMA(1974)

AfricaSudan (12)Latin America
Colombia (15)

0
80

9.811
12.230 25

0
60

FAO
30

64

CEA-IPI-ISMA(1974)

Appendix 2. Mean effect of phosphorus on yield
Country (No.
of annualkg
P205/ha

Yield
(tha)

Yield increase% kg tubers/

Referencekg P2 0 5

results)
EuropeEngland (16)

66

0
100

38.0
39.9

Archer et al. (1976)
5

19

Country (No.

kg

Yield

Yield increaseof annual
results)

P205/ha(t/ha)%England (16)England (16)Norway (46)

Norway (10)Poland (112)
Poland (90)
Poland (60)
Poland (48)

Sweden (68)

Asia
Cyprus (17)India (35)

200
300
400
500
0
100
200
300
0
34
69
0
55
108
0
120
0
120
0
120
0
36
72
0
92
183

41.6
9
42.9 1342.3 1I
42.7 1240.80
40.97 0.4
41.73 242.38 424.42
25.78 626.57 934.02
34.90 335.99 626.40
28.70 927.30
31.51 15
24.10
26.48 10
26.9
29.0
8
30.0 1230.1
32.7
933.8 12

0
60
119
179
0
112

30.5
31.4
32.0
32.2
20.60
22.07

Referencekg tubers/
kg P205

18
16
II
9
2
5
5

Farrar and Boyd(1976)

Furunes (1975)40
31
Ekeberg (1972)
16
18
19
35
20
58
43
28
20

3
5
6

15
13
9

7

13

Roztropowicz andFotyma (1978)
Roztropowicz andFotyma (1978)
Roztropowicz andFotyma (1978)
Boguszewski and
Pieczyrak (1968)
Hahlin andJohansson (1973)

Krentos and Orphanos(1979)

Raheja (1966) in:
Raychaudhuri(1976)

67

Country (No.

kg

Yield

Yield increaseof annual
results)

P205/ha(t/ha)%

Lebanon (25)Syria (12)Turkey (28)AfricaSudan(12)Appendix 3.

0
60

27

CEA-IPI-ISMA(1974)

080

8

CEA-IPI-ISMA(1974)

080

30

CEA-IPI-ISMA(1974)

040

Latin America
Colombia

12.23014.048

FAO
15

0
142

45

39

EuropeDenmark(13, cv. Bintje)

kg
K20/haYield(tlha)

Yield increasekg tubers/%
kg K20

Reference

H0jmark (1977)

0
108
217
325

36.4
37.6
38.3
38.1

3
5
5

11
9
5

Denmark(J1, cv. Saturna)

0
108
217
325

35.1
36.9
38.2
38.2

5
9
9

17
15
10

England (26)

0
100
200

33.0
34.9
35.4

6
7

19
12

300

35.9

9

10

0
188
282

35.9
40.9
41.6

14
16

27
20

68

CEA-IPI-ISMA(1974)

Mean effect of potassium on yield

Country (No.
of annual
results)

England (16)Referencekg tubers/
kg P2 0 5

Hojmark (1977)

Webber et al.
(1976)

Archer et al. (1976)

Yield increase% kg tubers/
kg K20

Reference

Country (No.
of annual
results)kg
K20/haYield(t/ha)England (16)

0
113
226
339
0
60
120
180
240

39.72
41.25
41.88
41.93

Germany (Fed.
Rep.) (30)

0
120
160
220
280

27.5
30.8
31.7
33.8
35.4

12
15
23
29

28
26
29
28

Netherlands (43)

0
150
300
600
1200

48.5
50.1
50.8
52.3
52.2

3
5
8
8

11
8
6
3

0
120
241

24.34
26.04
26.39

7
8

14
9

Norway (50=10
expts. with 5 cvs.)

0
84
169

28.77
30.31 531.55 1018
16

Norway (10)

0
75
148

33.44
35.20
36.24

5
8

23
19

0
120

26.10
27.89 16

15

Roztropowicz andFotyma (1978)

0
120

24.70
26.74

17

Roztropowicz andFotyma (1978)

Germany (Dem.
Rep.) (12)Norway (46)

Poland (116)
Poland (68)

4
5
6

14
10
7

Farrar and Boyd(1976)

Bruchholz (1974
and 1976)

9
16
18
15

Braunschweig, von(1972)

Prummel (1981)

Furunes (1975)

Ekeberg and Ronsen (1973)
Ekeberg (1972)

8

69

Yield increase% kg tubers/
kg K20

Reference

Country (No.
of annual
results)kg
K20/haYield(t/ha)

Poland (48)

0
80
160

27.1
28.8
29.8

6
10

21
17

0
120

24.10
26.08

8

17

Roztropowicz andFotyma (1978)

0
181

30.9
33.2

7

13

Hahlin andJohansson (1973)

0
56

22.07
22.93

4

15

India (15, local
cv.)

0
30
60

6.898
7.002
7.260

2
5

3
6

India (15, cv. Red
Patna)

0
30
60
0
51
102

9.656
10.1495
11.033 14
23.9
27.2
14
28.7
20

India (10, cv. Upto-date)

0
30
60

10.49411.34411.777

Lebanon (25)

0
120
0
40
80

12.19313.48414.028

II
15

32
23

0
77

9.10
15.07

66

78

Poland (34)
Sweden (68)

Boguszweski and
Pieczyrak (1968)

Asia

India (35)India (14, crop
affected by frost)

Pakistan (35)

S. Korea (56)Syria (12)

70

0
80

8
12

16
23
65
47
28
21
0.1

Raheja (1966), in:Raychaudhuri(1976)
Prasad and
Mahapatra (1970)
Prasad and
Mahapatra (1970)
Grewal and Singh(1980)
Prasad and
Mahapatra (1970)
CEA-IPI-ISMA(1974)
Manzoor Elahi Raja
and Abdul Hamid(1973), in: Kemmler(1978)
Hong (1977)

8

CEA-IPI-ISMA(1974)

Country (No.
of annual
results)kg
K20/haTurkey (28)080AfricaKenya(116)
Kenya (68)
Kenya (18)
Sudan (12)Latin America
Colombia (15)Ecuador(186)

0
60
0
60
0
67
0
40

Yield
(/ha)

Yield increase% kg tubers/
kg K201915.61517.75011.40113.36911.07712.40715.74417.882

36

17

33

12

20

14

53

Mathieu (1974)
Mathieu (1974)
FAO

21
9.832
10.557

CEA-IPI-ISMA(1974)
Mathieu (1974)

14

0
60
0
22.5

Reference

CEA-IPI-ISMA(1974)FAO (1974)

8

32

71

-4.

Appendix 4. Fertilizer recommendations (kg/ha N, P20 5, K20) in various countries
Remarks

Reference

100-350
60-250Maincrop
Earlies, industrial and seed

MAFF (1979)

150-180
80-120100-140
100-120125-160

150-200
150-200
180-240120-150
160-190

Earlies with FYM
Maincrop with FYM
Maincrop no FYM
Seed crop with FYM
Seed crop no FYM

Gros (1979)

150-200
100-140
80-120100-160

120-150
120-150
120-150
120-150200-320200-320200-320200-320

Early crop
Maincrop
Seed crop
Industrial and forage

Ruhr-Stickstoff AG(1980)

Germany (G.D.R.)

100-140
80-12040-100130-160
150-190

92-12892-13746-115104-128103-131

96-13596-14577-193125-154
145-183

Early crop
Maincrop
Seed crop
Starch production
ForageRinno (1973)

Greece

160

120

100

Ireland

100

100

200

30-2400-1000

N

P20 5

K 20

0-220
0-180

100-350200-350

France120-180
80-140100-170
30- 7045-100Germany (F.R.G.)

Country
EuropeEnglandNetherlands*

0-330

ISMA (1979)
ISMA (1979)
Maincrop

Consulentenschap voor
Bodemaangelegenheden inde Landbouw (1982)

Country

N

P20 5

K20

USSR

123
80-14060-10060-1201601207060-120193300
21060-120Asia
Bangladesh

168

112

112

Mahk et al. (1978)

India-Himachal Pradesh

75-10075-12580-125

Rajoo and Singh (1978)

Indonesia
Iran

100
90

100
45

50

De Geus (1973)
De Geus (1973)

Israel120-160

100

240Japan-Alluvial soils
Japan-Volcanic soils
Japan-Organic soils

80-12060-11050- 90140-150
170-180140-160

120
120
110-120

Pakistan-Punjab
Philippines

168
30

112
30

84
60

Kemmler (1978)
Abad

S. Korea

100

100

120

Taiwan150-200

150-200240-360

Assoc. for Potash Research(1980)Su (1972)

Turkey100-15060-10060-120IPI Program to Turkey (1980)

America
Brazil-Goias
Brazil-Parani

80-12060-100150-225
20-12050- 7560-150

Yamada (1980)

SwedenSwitzerland-

Remarks

Maincrop, forage and industrial
Seed crop
Non chemozem soils-

Reference
ISMA (1979)
Hasler et al. (1979)
Anon. (1978)

De Geus (1973)+20t/ha FYM+20t/ha FYM+20t/ha FYM+15t/ha compost

Kali Kenkyu Kai (1980)

CountryN

P2 0 5

K 20

Brazil-Slo Paulo60-100150-350

45-135

Remarks

Reference

Brazil-Cerrado soils

150

450

200

Colombia

200

390

90

ISMA (1979)

Dominican Republic

124-190124-2400-320Free et al. (1976)

Mexico

60

120

60

De Geus (1973)

Peru

120-200

80-2000-120Castafieda (1977)
Montelaro (1975)

USA-Florida

168-269
134-2010
67-134224
18060-180134

224-325
180-247
90-270134-201

USA-Massachusetts
USA-'Mid-Atlantic States'

179-202157

146-302112-224

146-302168-336

Lorenz and Maynard (1980)

USA-New Jersey

140-168

56-22456-336Anon. (1974)

Africa
Mauritius

78

78

120

Bazelet (1980)

South Africa

70-15040-1200-150

Bazelet (1980)

0-160

0-310

0-130

De Carvalho (1971)

Zimbabwe

Mineral soils irrigatedMineral soils not irrigatedOrganic soils
Marly soils* Fertilizer recommendations in the Netherlands are very sophisticated, especially in the case of potassium; therefore they vary greatly
according to soil texture, nutrient contents and to the intended use of potatoes.
Nitrogen: Soil reserves are taken into consideration and the following amounts are recommended: 330 kg/ha N - 1.5 x the soil reserve
for main crop potatoes and 140 kg/ha N - 0.6 x the soil reserve for seed potatoes.

Phosphate: Seed potatoes should receive higher rates than main crop potatoes and 30-240 kg/ha P20 5 are recommended for industrial
potatoes.
Potassium: The following rates are recommended (kg/ha K20):
Sandy and peaty soils
Clay soils <10% organic matterand alluvial clay soils
Clay soils >10% organic matter
Loess
Recent Zuiderzeepolder
K-fixing soils

Main crop potatoes
50-30060-380
0-280
0-340
0-280
210-530

Starch production
0-250
0-200
0-220
0-140
0-200
150-350

In order to reduce internal blackening of tubers, higher rates are recommended on clay soils, i.e. 110-1000 kg/ha K20 on soils<10% organic matter and 50-960 kg/ha K20 on soils >10% organic matter. Seed potatoes should receive higher potassium
dressings than main crop potatoes except on sandy and peaty soils where 50-300 kg/ha K20 are recommended.

"-J.

Appendix 5. Fertilizer rates (kg/ha N, P205, K20) used in various countries(FAO, 1988)
Country

N

P205

K20

AfricaAlgeria

210

180

180

Egypt

248

62

-

Mauritius
Nigeria
Togo

156
21
90

156
8
80

240
7
lO

Chile

77

70

-

Dominican Republic
Guatemala

110
129

95
58

95
193

Mexico

77

98

-

75
87
102

60
20
145

Remarks

America

Trinidad and Tobago
Uruguay
Venezuela

100
67
102

Asia
Bangladesh

55

-

68

Cyprus
Japan

200
105

130
173

50
110

Oman

96

48

-

Turkey

104

92

15

130
160
140
70
202
140
150
98
92
186

80
170
69
200
135
236
80
77
61
187

200
90
180
120
287
289
55
142
110
258

EuropeAustria
Bulgaria
Denmark
Finland
Hungary
Ireland
Spain
SwedenUnited Kingdom

76

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