EFFECT OF HARVEST METHOD AND FEED VALUE ON THE ECONOMIC OPTIMUM NITROGEN RATE FOR CORN

Consideration of the harvest method and protein content of corn grain and forage may be important variables for estimating Economic Optimum Nitrogen (N) (EON) rates for corn. Corn grain yield, forage yield, gra in protein and forage protein data from twenty five N response experim ents conducted in Pennsylvania were analyzed to determine the effect o f harvest method and a price adjustment based on grain and forage prot ein content on the EON rate. The value of the protein in this study wa s assumed to be that of substituting soybean meal in the ration for gr owing beef cattle or dairy cattle. There was no difference in the EON for corn harvested for grain compared to corn harvested for forage whe n the protein content was not considered. When price adjustments were made for the protein content of the grain and forage, the EON rates in creased 10 kg/ha for grain and 22 kg/ha for forage. With the protein p rice adjustments, the EON was 14 kg/ha higher for forage than grain. T hese results support the recommendation for higher N rates for corn ha rvested for forage, where the protein value of the forage is considere d, compared to corn harvested for grain. In situations where the amino acid composition of the grain is important, such as for poultry or sw ine, or where urea or anhydrous ammonia can be substituted in the rati on for protein, it is unlikely that a higher EON level would result wh en protein content or quality is considered.