As the weather turns cooler, cool-season grass pastures enter their most productive period of the year. For optimum production, producers need to apply sufficient fertilizer to these grasses in a timely fashion, says Dale Leikam, Kansas State University Research and Extension nutrient management specialist.
"Nitrogen, phosphorus, potassium, and sulfur are the nutrients which most commonly limit cool-season grass production in Kansas," he says.
If cool-season grass pastures have not been sampled yet for soil test analysis, the K-State agronomist said, it should be done at once.
"Cool-season grasses may need more than just nitrogen. Balanced fertility is essential to optimum yield and high quality hay. For example, adding nitrogen will not produce optimum yields if the soil phosphorus or potassium levels are low," Leikam says.
While the November-February time-frame is optimum for most fertilizer applications to many cool-season grass pastures, Leikam says there are situations where it might be best to split applications between an August-September application and a November-February application.
The conditions in which a split application might be preferred include:
- If the cool-season grass is to be grazed/harvested in both the fall and spring;
- If the cool-season grass stand has been subjected to drought or overgrazing stress; or
- If the field is to be used for seed production.
Do not apply nitrogen fertilizers to frozen soils, since there is a real potential of nitrogen washing off the field in runoff, Leikam adds.
For established stands of cool-season grasses, cool-season pastures should be fertilized with about 100 to 140 pounds of nitrogen per acre per year, he said. In central Kansas, the nitrogen rate should be about 60 to 100 pounds per acre. Other nutrients should be applied if needed, based on soil test values.
"Over the years, large amounts of phosphorus and potassium are removed from cool-season grass pastures, and phosphorus and potassium soil test values are often low. Cool-season grasses are relatively responsive to applied phosphorus and potassium if soil tests are low," Leikam says.
If the nitrogen, phosphorus, and potassium needs of the crop are completely satisfied, sulfur would be the most likely nutrient to limit cool-season grass production. A rate of 10 to 15 pounds of sulfur is the suggested rate of application, he adds.
Finally, soil pH is sometimes a consideration for cool-season grass pastures, Leikam added. "Both forage production and stand longevity are reduced when the soil pH is less than 5.5. At higher soil pH levels, however, cool-season grass responses to lime have been inconsistent in K-State tests. If lime is to be applied, surface-apply no more than 2,000 lbs effective calcium carbonate per acre at one time, Leikam says.
More information on smooth bromegrass management is available in the K-State publication C-402 "Smooth Brome Production and Utilization." It is available on the Web at: www.oznet.ksu.edu/library/crpsl2/c402.pdf.