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Turfgrass Fertility Needs of Cool-Season Grasses

Curtis E. Swift, Ph.D., Colorado State University, Area Extension Agent, Horticulture

Soil Test Levels (ppm)
Recommendations based on a soil test report (Ammonium Bicarbonate DPTA technique)

NO3-N (nitrate nitrogen) Level of sufficiency Requirement of N/year [1]
< 10 ppm very low 4- 5 applications (1 pound/1000 sq. ft)
10- 24 low 3- 4 applications (1 pound/1000 sq. ft)
25-49 medium low 2- 3 applications (1 pound/1000 sq. ft)
50- 74 sufficient apply (1 pound/1000 sq. ft)  when growth is less than desired
75- 100 high 0
> 100 very high 0 Check drainage; turf may be succulent and prone to disease and other problems
P (phosphorus) [8] Level of sufficiency P205/1000 sq. ft/year
< 5 ppm very low 4- 5 app. 0.5 lb.
5- 15 low 2- 3 app. 0.5 lb.
16- 30 medium low 1- 2 app. 0.5 lb.
31- 50 sufficient 0
51- 75 high 0
> 75 very high 0
K (potassium) Level of sufficiency K20/1000 sq. ft/year
< 25 ppm very low 4- 5 app. 0.5 lb.
25- 75 low 2- 3 app. 0.5 lb.
76- 150 medium low 1- 2 app. 0.5 lb.
151- 300 sufficient 0
> 500 very high 0 May indicate drainage problem
Fe (iron) Level of sufficiency [2] Fe recommendation/1000 sq ft area [3]
< 5 ppm very low 2 app. 0.5 lb. [4]
5- 14 low 1- 2 app. 0.5 lb. [5]
15- 20 medium low 1 app. 0.5 lb. [6]
21- 100 sufficient 0
>100 [7] high 0

Cu, Zn, Mn- add organic if less than 0.5 ppm.

[1] Use split applications; follow the late-season fertilization program.

[2] Low levels of available iron may indicate over-watering, poor soil preparation, excessive phosphorus levels, or soil compaction.

[3] If liquid is used apply according to label directions.

[4] First application of ferrous sulfate or ferrous ammonium sulfate in late May or early June, second about a month later.

[5] Apply 1 lb. of Fe/1000 sq. ft area. This may be sufficient for one season; if not, repeat application.

[6] Usually needed only if a very dark green lawn is desired.

[7] Often associated with acid soils that need liming; not typically a problem in Colorado.

[8]The extraction method used to determine the P in the sample needs to considered with using this fertility chart. Conversion information based on the extraction method used is provided at Phosphorus_analysis_techniques.shtml

Placed on the Internet September 21, 2004; Updated September 1, 2009; Updated April 25, 2011