Horticulture

Turfgrass Fertility Needs
by 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)

NO 3 -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

K (potassium)	Level of sufficiency	K 2 0/1000 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

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 1lb. 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.

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