Agri-Brief: Potassium Inceases Forage Yields, Quality, and Stand Persistence

AGRI-BRIEFS
AGRONOMIC NEWS ITEMS

From Agronomists of the
Potash & Phosphate Institute
655 Engineering Drive, Suite 110
Norcross, Georgia 30092-2837
Phone (770) 447-0335

Fall 1997, No. 6

POTASSIUM INCEASES FORAGE YIELDS, QUALITY, AND STAND PERSISTENCE

To capitalize on yield and quality opportunities, forage producers in the southern states should consider crop nutrient needs based on soil tests and harvest removal.

Good forage growth places a large demand on the soil's nutrient supplying power. Failure to replace harvested nutrients can result in a draw-down of the soil nutrient reservoir, reducing yields and shortening the life of alfalfa, clover, bermudagrass and other forage stands. Topdressing deficient pastures and hay meadows at the right time can lead to improved forage performance and enhance the opportunity to capitalize on good growing conditions.

Balanced fertilization, with particular attention to potassium needs, will help ensure that forage/ hay production and quality needs are met. Potassium removal by most forages is second only to the harvest removal of nitrogen. For example, hay harvests of bermudagrass, clovers, and alfalfa will all remove between 40 and 60 pounds of K₂O per ton. If eight 1,000-pound round bales of these forages are harvested per acre, as much as 160 to 240 pounds of K₂O per acre are also removed.

Failure to replace the harvested potassium in forages can result in :

Increased crop susceptibility to drought,
Increased susceptibility to diseases,
Decreased response to nitrogen and phosphorus applications
Thin stands with fewer leaves
Reduced forage quality
Increased susceptibility to winterkill and
Increased environmental losses of nitrogen through leaching and runoff.

For every pound of nitrogen removed in harvested bermudagrass forage, 0.75 to one pound of K₂O is also removed. For the dollar invested, potash is arguably among the most economical inputs a producer can purchase. For example, on a soil in Louisiana testing low in potassium, it took three years of applying at least 200 pounds of K₂O (330 pounds of 0-0-60 fertilizer) per acre to increase the bermudagrass stand to an optimum density. After harvest, fertilization and liming costs were considered, and assuming a hay value of $60 per ton, the net return to K₂O fertilization was over $16 per acre per cutting.

Leafspot disease organisms readily attack bermudagrass and other warm season forage grasses that have inadequate potassium levels. Tissue analysis can help identify potassium-deficient forages. Tissue concentrations should be at least 1.8 to 2.4 percent potassium in 3 to 5 week-old stands or regrowth. Maintaining adequate potassium levels through the summer into the late fall, before the onset of dormancy, helps plants manufacture carbohydrates for root growth and storage, improves water-use efficiency, enhances nitrogen-use efficiency, and helps plants compete with weeds. A healthy stand in the fall contributes to a rapidly growing, healthy stand the next spring.

Mid-season to late-summer application of potassium can increase forage production and profitability. Consider the potassium needs of your crops. Nitrogen, phosphorus, potassium, sulfur, magnesium and other essential nutrients must all be kept in balance to provide adequate forage production and nutrition_for beef cattle, dairy cattle, horses, sheep and goats. Be sure to include potassium in a balanced supply with nitrogen and phosphorus if planning to overseed warm season grasses with a cool season annual, such as ryegrass or wheat, to extend the grazing season.

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For more information, contact Dr. Cliff S. Snyder, Midsouth Director, PPI, P.O. Drawer 2440, Conway, AR 72033-2440. Phone (501) 336-8110. E-mail: csnyder@ppi-far.com.
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