K-State Research and Extension Johnson County

Fertilizer for Cool-season Grasses

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There is no one right answer to how to fertilize Cool-season grass. There are several options, and how you utilize your grass will help you decide how to fertilize. The number one key to fertilizing is to know what nutrients are deficient so that you can optimize the most bang for your buck. Ag producers in Johnson County are eligible for ten free soil tests through our office. This can be a great resource to help you make management decisions, and it’s free!

Fertilizing Cool-season Pasture Grasses

Smooth bromegrass and tall fescue, which are cool-season grasses, require annual fertilization for optimum production. Traditionally nitrogen (N) is the nutrient most commonly applied to cool season grass pastures and hayfields. But phosphorus (P), potassium (K), and sulfur (S) are other nutrients which commonly limit cool-season grass production in Kansas. If cool-season grass pastures and hayfields have not been soil tested yet, this should be done as soon as possible.

Cool-season Grass Fertility Programs

A good fertility program is essential for optimum yield and high quality hay. Adding N will not produce optimum yields if the soil P level is low. Plant and root growth will be limited if the soil’s ability to provide adequate P to cool-season grasses is limited. Likewise for K. In recent years, response to S has also become more common as the amount of S being added to our soils each year through deposition from the air has decreased sharply.

Splitting Fertilizer Applications

While the late-fall or late-winter timeframe is optimum for fertilizer applications to cool-season grasses, there are situations where it might be best to split applications between a late-summer/early-fall application and a late-winter/early-spring application. If split applications are used, it is best to apply all the P and K along with 30 - 50 lbs N per acre during August-September — while applying the remaining N and S fertilizer during the November - February time period. If split applications will not be used, it is best to apply all of the needed fertilizer in the winter to early-spring time period.

Under what conditions would a split application be preferred?

  • If the cool-season grass is to be grazed/harvested in both the fall and spring, it is best to make split applications in order to maintain adequate growth and quality for the fall crop.

  • If the cool-season grass stand has been subjected to drought or overgrazing stress, split applications are preferred in order to provide optimum nutrition for the recovering crop.

  • If the field is to be used for seed production.

Over the years, large amounts of P and K are removed from cool-season grass pastures, and P and K soil test values are often low. Cool-season grasses are relatively responsive to applied P and K if soil tests are low. Crop removal is about 12 pounds of P2O5 and 40 pounds of K2O per ton of cool-season grass. If maintaining soil test values is desired over time, then replacing the amounts of P and K removed in the forage will be required.

If the N, P, and K needs of the crop are completely satisfied, S would be the most likely nutrient to limit cool-season grass production. Application rates of 10-15 pounds/acre of S are suggested.

For more information on smooth bromegrass management, see K-State publication C-402 Smooth Brome Production and Utilization

Written by Juju Wellemeyer