Nutrient Requirements of Tropical Turfgrass1
Micah Woods, Ph.D.
11 March 2013This handout is a supplement to thepresentation given on this topic at theSustainable Turfgrass Managementin Asia 2013 conference at Pattaya,Thailand.
1High performance turf requires enough nutrients, and an importantquestion turfgrass managers must answer is “what amount of eachmineral nutrient should I supply to the grass?” By looking at what isin the grass and estimating how much is harvested when leaves areremoved from the plant, we can estimate how much of each element
is used. Another, more general approach, is to use the temperaturebased growth potential (GP) to predict the growth and the nutrient
use of the grass. Once we have that estimate of nutrient use, we cancompare the amount used to the amount available in the soil, andthat information forms the basis for the development of a sciencebased and efficient fertilizer program.

The logical place to start is to look at what is in the grassleaves. There are 14 essential mineral elements for plants (Table 1)
and 3 essential nonmineral elements. The nonmineral elements,
carbon, hydrogen, and oxygen, are taken up by plants as carbon
dioxide from the atmosphere and as water from the soil. Mineralelements are taken up by the roots and a portion of them can also
be absorbed through the foliage.

MineralHydrogen
OxygenCarbonNitrogenPhosphorus
Potassium
Calcium
Magnesium
SulfurBoron
Chlorine
Iron
Manganese
Zinc
CopperMolybdenum
NickelTable 1: The 17 essential elements forplants, divided into nonmineral andmineral

Leaf nutrient content and the controlling role of nitrogen
If we were to analyze the grass leaves for mineral nutrient content,
we would find nitrogen in the largest amount, usually at about 4%,
then potassium, usually at about 1.5% to 2%, and then phosphorus
and calcium, which are found in similar amounts, usually justunder 0.5%. Table 2 shows the relative amounts of the eight mineralelements found in the highest concentration in leaves.
Grass will grow faster when more nitrogen is applied. But turfgrass managers apply less nitrogen than the grass can use. It is
important to recognize that turfgrass managers use this techniqueto produce the desired growth rate and the desired turfgrass conditions. For both cool-season2 and warm-season grasses3 , the actual
amounts of nitrogen applied to the turf are considerably less thanwhat the grass can use.
Because nitrogen is the mineral element required in the largest
amount by the grass, and because nitrogen supply is always lessthan the grass can use, it becomes apparent that nitrogen controls
clipping production and thus nitrogen also controls the turfgrass
uptake of the other essential elements.

Nonmineral

Element

Percent %Nitrogen
Potassium
Phosphorus
Calcium
Magnesium
SulfurIron
Manganese

420.50.5
0.2
0.1
0.01
0.005

Table 2: Approximate percentage ofthe most abundant mineral elements inthe leaves of many turfgrass species
Wayne Kussow and Steven Houlihan.
The new soil test interpretations for
Wisconsin golf turf. The Grass Roots,
pages 19–25, May-June 2006
2E.A. Guertal and D.L. Evans. Nitrogen rate and mowing height effects on
TifEagle bermudagrass establishment.
Crop Sci., 46:1772–1778, 2006; and L.E.
Trenholm, A.E. Dudeck, J.B. Sartain,and J.L. Cisar. Bermudagrass growth,
total nonstructural carbohydrate concentration, and quality as influenced
by nitrogen and potassium. Crop Sci.,
38:168–174, 1998
3

nutrient requirements of tropical turfgrass

2

How much is removed by mowing
Mowing removes nutrients from the grass by cutting theleaves. In the situation where clippings are returned to the turf,
most of the nutrients are recycled by the turf. When clippings areharvested, as is the common practice on golf course putting greensand other high maintenance turfgrass areas, the nutrients in theleaves are removed with the clippings.
During periods of active growth, when maintained using standard management techniques and nitrogen rates, I estimate thatmaximum clipping removal from turfgrass4 may be about 100 to
125 grams of dry matter per m2 per month.
One of the ways we can determine the nutrient requirement is
simply to replace the nutrients that are removed by mowing. However, we cannot measure the exact amount of leaf clippings that areharvested. Also, the growth rate of the grass changes throughout
the year in response to temperature, soil moisture, and light intensity. Because we are not able to measure the exact nutrient loss bymowing, a general model of growth can help us to predict nutrient
requirements.

Temperature-based growth potential
The growth potential (Equations 1 and 2) was developed
by PACE Turf 5 to describe the relationship between turfgrass
growth and temperature. Cool season (C3 ) grasses have their greatest growth rate when the temperature is about 20°C, with slower
growth at lower or higher temperatures; warm-season grasses (C4 )have their greatest growth rate when the temperature is 31°C orabove, with slower growth at cooler temperatures. The growth potential provides a simple way to predict that growth.6
t−to 2

GP = e−0.5( var )(1)

GP = growth potential, on a scale of 0 to 1
e = 2.71828, a mathematical constantt = average temperature for a location, in °C
to = optimum temperature, 20 for C3 grass, 31 for C4 grass
var = adjusts the change in GP as temperature moves
away from to ; I use 5.5 for C3 and 8.5 for C4

Tim L. Springer. Biomass yield froman urban landscape. Biomass andBioenergy, 37, 82-87 20124Wendy Gelernter and Larry Stowell.
Improved overseeding programs
1. the role of weather. Golf Course
Management, pages 108–113, March2005
5A more complex growth model
would require information that is
not readily available, namely themaximum potential growth rate of a
specific grass variety combined with,at a minimum, knowledge of the effectof temperature, plant water status, leaf
nitrogen content, and photosynthetic
irradiance on the growth of the grass.
The temperature-based growth potential is a simplification but it is easy touse and effective as a planning andmanagement tool.
6For the equations using the Fahrenheit
temperature scale, see Gelernter &Stowell (2005). Use a variance of 7for C4 grasses if you want to match
almost exactly the results of Gelernter& Stowell. Variance of 8.5 predicts
slightly more growth away from theoptimum temperature than does theoriginal equation.

This equation gives the same result.
GP =1(2)t−to 2e0.5( var )Figure 1 shows the growth potential as calculated by equation 1
across the range of temperatures from 0 to 31°C. For warm-season
grasses, the growth potential rises above 0.1 at 13°C. We can interpret a growth potential of 0.1 as being 10%, and at that tempera-Figure 1: The predicted growth potential for cool-season (C3 ) and warmseason (C4 ) grasses

nutrient requirements of tropical turfgrassture, all other things being equal, the grass would have the potential to grow at about 10% of its maximum rate. At a temperature of17°C the growth potential for warm-season grass reaches 0.25, andthis model predicts that 21°C is an average temperature at which
growth potential will be 0.5.
Above an average temperature of 25°C, this model predicts
warm-season grass will have a growth potential more than 0.75.
For cool-season grass, the growth potential declines quickly7 above
a temperature of 25°C. At a location such as Bangkok or Singapore,
the average temperature is always above 25°C, and thus the warmseason growth potential is always above 0.75 in those locations. In
looking at Hong Kong, Shanghai, and Sydney (Figure 2) we can see
the seasonal changes that occur in growth potential.

Hong Kong is slightly warmer, on average, than Shanghai, sowe can see that the growth potential for warm-season grasses isslightly higher at Hong Kong than at Shanghai. And we also cansee that average temperatures at Sydney are more moderate, withcooler summers than both Hong Kong and Shanghai, but with awarmer winter than Shanghai and only a slightly cooler winterthan Hong Kong. The growth rate and consequently the nutrient
requirements of the grass are strongly influenced by temperature,and we can use the growth potential to predict the nutrient requirements of the turf.

The reason for this rapid decline isphotorespiration, which increases
more rapidly than photosynthesis
as temperatures rise above 20°C.
Photorespiration, which occurs in
C3 grasses but not in C4 grasses,
essentially undoes the reactions ofphotosynthesis.
7

Figure 2: Growth potential calculatedusing equation 1 based on averagemonthly temperatures for these cities3

nutrient requirements of tropical turfgrass

4

Linking the leaf nutrient content with growth potential to predict
nutrient requirements
Nitrogen
We can make use of the growth potential by relating the nitrogen requirement of the grass to the growth potential. Empiricalobservations of turfgrass growth rates and nitrogen amounts tocreate the desired playing conditions for golf course turf in 2013
give us a maximum monthly nitrogen use rate8 of about 4 g N m-2
for bermudagrass (Cynodon) and 3 g N m-2 for seashore paspalum(Paspalum vaginatum) and manilagrass (Zoysia matrella).
When the growth potential is 1, the grass can grow at its maximum rate, the clipping harvest of nutrients will be at a maximum,
and that is when the estimated nitrogen use rate will be at a maximum. When the growth potential is less than 1, the clipping harvest
will be less than the maximum, and thus the nitrogen use of thegrass will be correspondingly less. And when the growth potential
is 0, the grass will not grow at all, the clipping harvest of nutrients
will also be 0, and the nitrogen use rate will be 0.
We can then simply calculate the estimated nitrogen requirement
for a given amount of time by multiplying the growth potential
times the maximum monthly nitrogen rate.

These estimates are general and only
serve as a starting point. Every golfcourse will have a slightly different
maximum level, based on the desired
growth rate of the grass. We canmake the grass grow faster withmore nitrogen, and slower with lessnitrogen, and these values are basedon standard conditions.
8Potassium
As shown in Table 2, the average potassium content of turfgrassleaves is usually about half that of nitrogen. The potassium requirement of the grass, then, is about half that of nitrogen. If themaximum nitrogen rate were 4 g m-2 mo-1 , then the maximum
potassium rate would be 2 g m-2 mo-1 . Adding more potassium
than the grass can use9 will not provide any benefit to the grass.
Even in situations when the soil contains as much or moresodium than potassium, it is not necessary to apply extra potassium, at least for bermudagrass turf.10

Other elements, with calcium as an example
The same approach as used for potassium can be applied to theother elements. We can use the growth potential to predict how
much the grass may grow, and consequently how much of an element it may use at any time, recognizing that nitrogen controls theuptake of the other mineral elements.
Let’s take calcium as an example, for a bermudagrass green at
Bangkok in the month of March. The growth potential at Bangkok
in March is 0.96. For simplicity let’s just round that up to 1. And
let’s assume that we have decided that our desired growth rate forbermudagrass is achieved at a maximum monthly nitrogen use of
4 g m-2 . The ratio of nitrogen to calcium in bermudagrass leaves isGrady Miller. Potassium application
reduces calcium and magnesium
levels in bermudagrass leaf tissueand soil. HortScience, 34(2):265–268,
1999; George H. Snyder and John L.
Cisar. Nitrogen/Potassium fertilization
ratios for bermudagrass turf. Crop
Sci., 40:1719–1723, 2000; and Micah S.
Woods, Quirine M. Ketterings, andFrank S. Rossi. Measuring the effectsof potassium application on calcium
and magnesium availability in acalcareous sand. International TurfgrassSociety Research Journal, 10(2):1015–1020, 2005
9George H. Snyder and John L. Cisar.
Potassium fertilization responses asaffected by sodium. InternationalTurfgrass Society Research Journal, 10:428–435, 2005
10

nutrient requirements of tropical turfgrassabout 8:1, with there being close to 4% nitrogen in leaves compared
to about 0.5% calcium. So if we estimate that the grass is using 4 g
N m-2 in March, then it can only use 1/8th as much calcium, or 0.5
g m-2 .
Using a spreadsheet or other software program, it is a matter ofjust a few minutes to estimate nutrient use rates of the grass at yourlocation given your desired maximum growth rate.11
But simply knowing how much the grass is using is not enough.
If there is already enough of an element in the soil, adding more as
fertilizer will have no effect on the grass.

5

The growth potential can be applied
on a daily, weekly, or monthly basis,
as can the associated nutrient use
estimates. To get annual estimates ofnutrient requirements, as shown in
Table 3, we can sum the daily, weekly,
or monthly estimates.
11

How much is harvested relative to how much is in the soil
The previous sections have described how to estimate the nutrients that are used by the grass. In that sense we may say they arerequired by the grass. But are they required as fertilizer? They are
if there is not enough of the element available in the soil to meetthe plant requirements. But for most elements other than nitrogen,phosphorus, and potassium, the amounts in the soil are usually
sufficient to meet the needs of the grass.
The minimum levels for sustainable nutrition (MLSN) guidelines
have been developed12 to provide guidance to turfgrass managers
in soil test interpretation and especially in determining whether
the amount of an element in the soil is adequate to meet the plantrequirements. The latest version of the MLSN guidelines can be
downloaded at http://www.paceturf.org/PTRI/Documents/1202_
ref.pdf.
Taking the location of Bangkok as an example, using the growthpotential model, and setting a maximum nitrogen rate for bermudagrass of 4 g N m-2 , we have an estimated annual harvest of elements as shown in Table 3. The MLSN guidelines are shown forreference, and it is clear in comparing the estimated use of elements
by the grass with the amount in the soil at the MLSN guideline that
only nitrogen, potassium, and phosphorus tend to have an estimated harvest greater than the amount in the soil. Calcium, magnesium, and sulfur, however, even at the low MLSN guideline, arepresent in the soil at greater amounts than the grass is estimated touse in one year, and thus they are rarely required as fertilizer.
Element

Estimated harvest
g m-2 yr-1

MLSN
ppm

MLSN
g m-2

Deficitg m-2

NKPCaMgS44.6
22.3
5.6
5.6
2.2
1.1

na
35
18360
54
13na
5.2
2.7
53.7
8.1
1.9

-44.6
-17.1
-2.9
none
none
none

Micah S. Woods and Larry Stowell.
Minimum levels for sustainable nutrition soil guidelines. Technical report,
Asian Turfgrass Center and PACE Turf,2012
12Table 3: Estimated annual harvest ofN, K, P, Ca, Mg, and S from bermudagrass at Bangkok assuming maximum
N rate of 4 g N m-2 mo-1 when growthpotential is 1. The current MLSN
guidelines are shown in both ppm andequivalent g m-2 units. Deficit shows
the amount the estimated harvest will
exceed the MLSN guideline.