Using temperature to predict turfgrass growth potential(GP) and to estimate turfgrass nitrogen use
Micah Woods, Ph.D.*ABSTRACT
Based on the optimum temperatures for turfgrass
growth, generally considered to be in the range of
16 to 24°C for cool-season grasses and 27 to 35°C
for warm-season grasses, it is possible to model thepotential for the grass to grow at any temperature.
This is the turfgrass growth potential (GP), a value
ranging from 0, meaning no growth is possible, to1, meaning the temperature is at an optimum forthat grass to grow. The GP is useful in turfgrassmanagement planning. This document describes
how to calculate GP and introduces one practicalapplication of this model: estimating turfgrass ni- Figure 1: For both cool-season and warm-season
trogen requirements.
grasses, the growth potential can be used to predict how temperature will influence the growth ofany grass, anywhere in the world: a) December,
Barcelona; b) June, Sydney; c) September, Tokyo;d) February, Bangkok.
rasses that utilize the C3 photosynthetic pathway are termed cool-season grasses and can growmost rapidly at a temperature of 16 to 24°C. simple, the GP can be understood as a way to put aGrasses that use the C4 photosynthetic pathway numerical value on the ability of the grass to groware able to photosynthesize efficiently at high tem- at a certain temperature.
The GP (Equations 1 and 2) was developed byperatures. These are termed warm-season grasses
PACE
Turf (Gelernter and Stowell, 2005) to deand are expected to grow most rapidly at a temperscribe
the relationship between turfgrass growth
ature range of at least 27 to 35°C.
andtemperature.
The equation to calculate GP
In addition to temperature, the leaf nitrogen stacompares
theactualtemperature to the optimum
tus, plant water status, and the quantity of photemperature
forgrowth,and then returns a value
tosynthetically active radiation (PAR) all influence
between0and1.
Low
valuesof GP predict slow
turfgrass growth. These four factors – temperagrowthorif
thevalue
iscloseto0, dormant turf.
ture, nitrogen, water, and light – essentially conAt
avalueof0.5,
theGP predicts that temperatures
trol how the turf will grow. Turfgrass managers
can easily modify the nitrogen and the water, but are such that the grass can grow at 50% of its maximum rate, and when the GP is 1, grass has the pocan do very little about the temperature or light.
By estimating the growth potential (GP), the in- tential to grow at its maximum rate.
Because turfgrass management, at its core, is refluence of temperature on turfgrass growth at any
allyabout controlling the growth rate of the grass,given time can be predicted. Knowing and anticiit
canbe useful to assign a numerical value to thepating the effect of something that cannot be coneffectoftemperature on growth. This index is GP.
trolled allows turfgrass managers to refine the turfgrass practices that can be adjusted.

GCalculating the growth potential
What is growth potential?
Turfgrass managers know that grasses change
their growth rate as the temperatures change
throughout the year, or as different grasses aregrown in different climates (Figure 1). At its mostWe start by identifying the center of the optimum
temperature range. For cool season (C3 ) grasses,
which have an optimum range of 16 to 24°C, this is20°C. For warm-season (C4 ) grasses, with the optimum range of 27 to 35°C, this is 31°C1 . As the* Chief Scientist, Asian Turfgrass Center,
http://www.asianturfgrass.com

1 Although growth of C grass declines as temperatures in3
crease beyond the optimum range, for C4 grasses there is not

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G ROWTH P OTENTIAL , J UNE 2013

ReykjavikLondon

VancouverBarcelonatemperature−based growth potential (GP)

1.00

●
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0.75

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●

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0.25
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Tokyo

●
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●

●

●

●

●

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1.00

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●

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Bangkok
●

● ● ●

●

●

●

● ●

●

● ● ●

● ●

●

●

●

●

●

●

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0.50

●

●

●

Miami
●

●

●

● ●

Sydney

● ●

0.75

●

●
●

●

●

●

0.25
0.00

●

●

●

0.50

0.00

●
● ●

●

●

●

●

● ●

1

3

5

7

911

1

3

5

7

9111357

911

13

5

7

911

MonthFigure 2: Growth potential of eight cities calculated using Equation 1; for Miami and Bangkok thewarm-season GP is shown; all other cities are shown with cool-season GP.
temperature moves away from the optimum, theThe equation written in this form (Equation 2)
potential of the grass to grow at its maximum rate gives the same result:is decreased. The GP provides a simple way to pre1
dict that growth.2 Equation 1 gives the standard(2)
GP =o 20.5( t−tvar )eform of the growth potential equation:
The GP can be easily calculated using a spreadt−to 2GP = e−0.5( var )(1) sheet formatted for your own requirements. PACE
Turf have also prepared a spreadsheet for calwhere,culating the monthly GP. This can be downloaded at http://www.paceturf.org/index.php/
GP = growth potential, on a scale ofpublic/ipm_planning_tools as the Climate Ap0 to 1
praisal Form which is conveniently available ine = 2.71828, a mathematical constantboth metric and Fahrenheit temperature scales.
t = average temperature for a location, inThese spreadsheets have also been formatted to°Ccalculate an estimate of monthly nitrogen requireto = optimum temperature, 20 for C3
ments.
grass, 31 for C4 grass
Figure 2 shows the GP for eight world cities, onvar = adjusts the change in GP as tempera monthly basis, and those same data are shownature moves away from to ; I suggest 5.5
in Table 1. The average temperatures used infor C3 and 73 for C4
Equation 1 to calculate monthly GP for these cities
are from the World Meteorological Organizationsuch a decline because photorespiration does not occur. The
climatological normals data, available at http://actual growth of C4 grasses seems to remain constant or actually increase as temperature rise above the optimum range. For www.wmo.int/datastat/wmodata_en.html.
practical purposes of using the GP, this does not matter because
the average temperature, even in the hottest locations at which
turfgrass is grown, remain within the optimum range.
2 A more complex growth model would require informationthat is not readily available, namely the maximum potential
growth rate of a specific grass variety combined with, at a minimum, knowledge of the effect of temperature, plant water status, leaf nitrogen content, and photosynthetic irradiance on thegrowth of the grass. The temperature-based growth potential isa simplification but it is easy to use and effective as a planningand management tool.
3 For the equations using the Fahrenheit temperature scale,see Gelernter & Stowell (2005). I sometimes use a variance of
8.5 for C4 grasses; a variance of 7 for C4 grasses matches almost

G ROWTH P OTENTIAL , J UNE 2013

Estimating
ments

nitrogenrequire-One of the most useful applications of the GP is inestimating how much nitrogen the grass may use.
Because the GP is a value between 0 and 1, we canexactly the original equation of Gelernter & Stowell. Varianceof 8.5 predicts slightly more growth away from the optimum
temperature than does the original equation.

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MonthReykjavik

LondonVancouverBarcelonaTokyo

SydneyMiami

Bangkok

1
2
3
4
5
6
7
8
9
10
11
12

0.00
0.00
0.00
0.01
0.04
0.14
0.23
0.21
0.07
0.02
0.00
0.00

0.01
0.01
0.03
0.09
0.29
0.60
0.82
0.78
0.53
0.24
0.05
0.02

0.01
0.02
0.04
0.13
0.36
0.68
0.88
0.89
0.58
0.19
0.04
0.01

0.13
0.16
0.27
0.43
0.76
1.00
0.87
0.86
0.98
0.87
0.39
0.17

0.03
0.03
0.11
0.56
0.97
0.95
0.64
0.43
0.84
0.91
0.40
0.09

0.90
0.88
0.96
0.99
0.78
0.51
0.42
0.53
0.76
0.95
1.00
0.95

0.27
0.31
0.45
0.61
0.77
0.88
0.92
0.92
0.89
0.75
0.53
0.33

0.77
0.88
0.95
0.98
0.96
0.95
0.93
0.93
0.91
0.91
0.86
0.74

Table 1: Calculated GP for C4 grasses at Miami and Bangkok and for C3 grasses at other cities, by month,using Equation 1.

simply choose the maximum amount of nitrogenthat we would want to apply in a day, week, ormonth, and then multiply that by the GP to givethe predicted amount of nitrogen the grass will use
during that time. If we set a maximum amount ofnitrogen that the grass may use at one time, thenas the GP decreases, so also will the predicted nitrogen use decrease.
The GP is based on the optimum temperatures
for photosynthesis of C3 and C4 grasses. In orderto produce maximum carbohydrates and roots, it
makes sense to ensure the grass is supplied withnitrogen in adequate amounts corresponding to
the ability of the grass to photosynthesize. Whenthe grass is not able to grow because temperatures are too cool, there is little reason to supply
nitrogen. Using the GP to predict how much nitrogen the grass may use throughout the year as
the temperature changes offers turfgrass managers
another tool to optimize the plant’s carbohydrate
production.
Estimated nitrogen use of the grass, based onmaximum monthly use of 3.5 g N m-2 for C3species and 4 g N m-2 for C4 species, is given in Table 2. These data are the result of multiplying themonthly GP by the selected maximum monthly Nrate.4
The maximum nitrogen rate is something that isvery site-specific. As an example, If I were growing fine fescue (Festuca spp.), I may set the maximum nitrogen at about 1.5 g N m-2 mo-1 . I would
never use 3.5 g N m-2 for that grass. Not only canone change the maximum nitrogen amount basedon grass species, but one must adjust the maximum nitrogen rate based on what type of turfgrass conditions one is trying to produce. I findit most useful to slightly underestimate how much
N the grass may use. Remember, we can always
put more fertilizer, but if we have put too much,
we can’t take it back.

At Sydney, I might set the maximum at 2 g N
m-2 mo-1 , which gives an annual estimated N use
of 19.2 g N m-2 . Then, if I were using a growth regulator such as trinexapac-ethyl, I would reduce theN rate a further 20% or so. But I could still use theGP and these simple calculations to estimate when
the grass would use the most N.
At Reykjavik, recognizing that there is a large
amount of traffic on the turf during the long summer days, and seeing that the temperatures are socool that the grass is not easily able to grow quickly
to recover from that traffic, I may set the maximum
at 5 g N m-2 mo-1 .

Applications, modifications, andextensions

Use of GP is not something that is fixed or must be
done in a certain way. The GP is not how the grass
grows – GP is not reality. What it is, however, isa simple method that can be used to estimate thereality of how grass grows, and can then be put touse to assist in turfgrass management.
As an example, one may choose to set an optimum temperature (to in Equation 1) of 18°C for
Poa annua rather than the standard 20°C for C3grasses. And if I were working with GP for kikuyugrass (Pennisetum clandestinum), I would use an
optimum temperature of about 25°C, rather than
the standard of 31°C used for other warm-season
grasses. The idea is to use GP to represent the reality of how turf growth is influenced by temperature. GP is simply an index of how the turf may
grow, and the turf manager can put this index touse in a number of ways.
One can make long-term plans by looking at average monthly, weekly, or daily temperatures, calculating the relevant GP, and planning based on
those normal temperatures. One can also make4 A simple conversion factor for fertilizers is to rememberthat 5 g N m-2 is equivalent to 1 lb N/1000 ft2 ; 1 g N m-2 is short-term plans by looking at forecast temperaequivalent to 0.2 lb N/1000 ft2 .
tures for the next day or week, calculating an ac3

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G ROWTH P OTENTIAL , J UNE 2013

MonthReykjavik

LondonVancouverBarcelonaTokyo

SydneyMiami

Bangkok

123
4
5
6
7
8
9
10
11
12

0.0
0.0
0.0
0.0
0.2
0.5
0.8
0.7
0.3
0.1
0.0
0.0

0.0
0.0
0.1
0.3
1.0
2.1
2.9
2.7
1.9
0.8
0.2
0.1

0.0
0.1
0.2
0.4
1.2
2.4
3.1
3.1
2.0
0.7
0.1
0.0

0.4
0.6
0.9
1.5
2.7
3.5
3.0
3.0
3.4
3.0
1.4
0.6

0.1
0.1
0.4
2.0
3.4
3.3
2.2
1.5
3.0
3.2
1.4
0.3

3.1
3.1
3.4
3.5
2.7
1.8
1.5
1.9
2.7
3.3
3.5
3.3

1.1
1.2
1.8
2.4
3.1
3.5
3.7
3.7
3.6
3.0
2.1
1.3

3.1
3.5
3.8
3.9
3.9
3.8
3.7
3.7
3.6
3.6
3.4
3.0

Annual

2.6

12.1

13.4

24.2

20.9

33.7

30.5

43.1

Table 2: Example of monthly and annual estimated nitrogen requirement of grasses, in units of g N m-2 ,based on a maximum monthly application of 4 g N m-2 at Miami and Bangkok and 3.5 g N m-2 at theother locations.

3. Turfgrass nitrogen requirement and growth
tual GP based on the current situation rather thanpotential, http://bit.ly/NGD58X
on the average.
For C3 grasses, high-temperature stress can be a
4. En español, Predecir los requerimientos
concern. Based on the adjustments one makes tonutricionales y el crecimiento del césped,
Equation 1, one can get an index of just how much
http://files.asianturfgrass.com/gp_
stress the grass may be under during the hottest
aedg_abril_2013.pdf
months of the summer.
I think it is interesting to look at GP before
5. 日 本 語 で, 芝 草 の 栄 養 要 求 を 理 解 す る,
scheduling core aerification and other disruptive
http://calendar.asianturfgrass.com/
maintenance practices. I always like to minimize
understanding_turfgrass_nutrient_disruption to the playing surface, and if theserequirements_5june2012_jp.pdf
maintenance activities can be scheduled at a timewith a high GP, the recovery time will be fast, andThese documents also provide additional expladisruption time minimized.
nations of GP and its practical use.
Nitrogen is not the only element that can be• This article from GCM explaining GP:
managed based on GP. For many turfgrass sites
http://www2.gcsaa.org/GCM/2005/
the amount of nitrogen applied controls the uptake
march05/pdfs/Weatherrole108-113.pdf
of other macronutrients (Petrovic et al., 2005; Kussow and Houlihan, 2006), and therefore the GP ap• Blog post from Jason Haines explaining
proach could easily be adapted for those elements
how he uses GP to optimize turfgrass peras well.5
formance at Pender Harbour Golf Club:
http://penderharbourgolf.blogspot.ca/
2012/09/how-much-nitrogen.html
More information
I have written extensively about GP and its application in turfgrass management. These documents
provide more information and examples.
1. Understanding turfgrass nutrient requirements, http://calendar.asianturfgrass.
com/understanding_turfgrass_nutrient_requirements_5june2012.pdf

References
Wendy Gelernter and Larry Stowell. Improved
overseeding programs 1. The role of weather.
Golf Course Management, pages 108–113, March2005.

Wayne Kussow and Steven Houlihan. The new soil
2. Nutrient requirements of tropical turftest interpretations for Wisconsin golf turf. Thegrass, http://www.files.asianturfgrass.
Grass Roots, pages 19–25, May-June 2006.
com/20130311_woods_handout_nutrient_A.M. Petrovic, D. Soldat, J. Gruttadaurio, andrequirements_tropical_turfgrass.pdf
J. Barlow. Turfgrass growth and quality re5 This approach is implemented in the minimum levels
lated to soil and tissue nutrient content. Interfor sustainable nutrition (MLSN) guidelines. For more infornational Turfgrass Society Research Journal, 10:989–mation see http://www.paceturf.org/index.php/journal/
997, 2005.
minimum_level_for_sustainable_nutrition.
G ROWTH P OTENTIAL , J UNE 2013

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