Trying to decide how much fertilizer to use in fields producing forage grasses is a challenge. Forage grasses often do best with nitrogen, phosphorus and potassium fertilizers, but increasing one can reduce the effects of the others. Producers sometimes apply more fertilizer than needed, which wastes money, causes excessive runoff and harms the environment, according to the U.S. Department of Agriculture.
By studying the effects of nutrients applied at different rates, a researcher with the USDA's Agricultural Research Service (ARS) in Georgia developed a formula for optimally fertilizing fields used to produce forage grass in southeastern U.S. The improved formula should curb runoff and reduce costs for beef and dairy producers in the Southeast who raise their own forage.
William F. Anderson and his colleagues with the ARS unit in Tifton, Ga., fertilized a commonly used forage grass at six different application rates for nitrogen fertilizer and at three different rates for the phosphorus and potassium fertilizers. They chose Tifton 85 as the forage in their study because it's a type of bermudagrass produced on millions of acres from Texas to the Carolinas to Florida.
Current fertilizer recommendations for Tifton 85 are based on outdated studies conducted for other types of bermudagrass, ARS noted.
The researchers used fields with two soil types common in the Southeast, kept track of rainfall amounts and evaluated yields and the hay's nutritional value (crude protein levels) for each application rate. They also tracked fuel and fertilizer costs and market prices for the hay in order to calculate which application rates are most likely to return the highest profits.
ARS reported that the researchers found the optimal application rate of nitrogen fertilizer to be about 300-400 lb. per acre, which was in roughly the mid- to low-range of the application rates evaluated. The results also showed that a 4:1:5 ratio of nitrogen to phosphorus to potassium works best for maximizing profits, assuming typical rainfall patterns. In other words, for every four parts of nitrogen applied, growers should apply one part phosphorus and five parts potassium, ARS explained. At those rates, a field will produce about 8-10 tons of hay per acre, assuming typical rainfall.
Results were published in May 2016 in Agronomy Journal.