AGRONOMIC NEWS ITEMS
From Agronomists of the
Potash & Phosphate Institute
655 Engineering Drive, Suite 110
Norcross, Georgia 30092-2837
Phone (770) 447-0335
Fall 1996, No. 2
HAY AND SILAGE HARVESTS REMOVE LARGE AMOUNTS OF POTASSIUM
For some cattlemen, 1996 beef prices and drought forced a reduction in herd size. Animals that remain will be more reliant on forage than in the past since grain prices are not predicted to decrease in the foreseeable future. Drought in some areas of the country and the lower cattle prices have allowed others to selectively expand their herds where moisture was less limited and forage was abundant.
Management should focus on optimizing forage production to minimize the per unit cost of animal weight gain and decrease the need for supplemental grain feeding. Balanced fertilization, with particular attention to potassium needs, will help ensure that forage/hay production and quality needs are met. Planning now will lead to improved performance and enhance the opportunity to capitalize on any rebound in cattle prices in the future.
In the South, some grain sorghum and corn fields were mowed and baled for hay or cut for silage to prevent a complete loss in cash flow as the crops withered from lack of moisture. A common assumption is that all the phosphate and potash applied in the spring will still be in the soil for use by late summer grass growth or fall crop needs. A review of potassium removal in hay and silage illustrates the error in this assumption and exposes the need for late summer and early fall potassium fertilization.
More potassium is removed in the harvest of corn and sorghum hay and silage than is removed by the harvest of grain only. Corn and sorghum silage, at 65 percent moisture and yielding 8 to 10 tons per acre, will remove from 64 to more than 80 pounds of K2O per acre. Hay harvests of sorghum, corn, and bermudagrass will remove between 40 and 60 pounds of K2O per ton. When eight 1,000-pound round bales are removed per acre, as much as 160 to 240 pounds of K2O per acre are also removed. This level of potash removal is second only to the removal of nitrogen by harvested crops.
Failure to replace harvested potassium can result in :
- increased crop susceptibility to drought,
- increased susceptibility to diseases,
- decreased response to nitrogen and phosphorus applications, and
- reduced forage quality .
Potassium deficiency in bermudagrass pastures and meadows also results in thinning stands with fewer leaves, increased susceptibility to winter-kill, poor early-season growth when moisture is most abundant, decreased forage digestibility, and a possible decrease in animal intake.
Nitrogen, phosphorus, potassium, sulfur and magnesium must all be kept in balance to provide adequate forage production and nutrition...for beef cattle, dairy cattle, horses, sheep and goats. For every pound of nitrogen removed in harvested forage, up to a pound of K2O is also removed. For the dollar invested, potash is among the most economical inputs a producer can purchase. In Louisiana for example, on a soil 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 costs and 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 hay cutting.
Consider the potassium needs of your crops now. Late -summer application of potassium can increase forage production and profitability. For those planning to overseed with a cool season annual…such as ryegrass or wheat...to extend the grazing season, be sure to include potassium in a balanced supply with nitrogen and phosphorus.
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