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 |
|< 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|
|> 100||very high||0 Check drainage; turf may be succulent and prone to disease and other problems|
|P (phosphorus) ||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.|
|> 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.|
|> 500||very high||0 May indicate drainage problem|
|Fe (iron)||Level of sufficiency ||Fe recommendation/1000 sq ft area |
|< 5 ppm||very low||2 app. 0.5 lb. |
|5- 14||low||1- 2 app. 0.5 lb. |
|15- 20||medium low||1 app. 0.5 lb. |
Cu, Zn, Mn- add organic if less than 0.5 ppm.
 Low levels of available iron may indicate over-watering, poor soil preparation, excessive phosphorus levels, or soil compaction.
 If liquid is used apply according to label directions.
 First application of ferrous sulfate or ferrous ammonium sulfate in late May or early June, second about a month later.
 Apply 1 lb. of Fe/1000 sq. ft area. This may be sufficient for one season; if not, repeat application.
 Usually needed only if a very dark green lawn is desired.
 Often associated with acid soils that need liming; not typically a problem in Colorado.
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