Nutrient Management in Mid-Atlantic Organic Grain Cropping Systems.

Farmers typically use animal manure or compost to maintain soil fertility. While these materials have N:P ratios of approximately 2:1 and 1:2, respectively,  most crops have ratios between 7:1 and 10:1. Manure applications sufficient to meet crop N needs thus typically provide excessive amounts of P, which, with repeated applications, can result in increased risk of P losses to surface runoff. In watersheds such as that of the Chesapeake Bay, the P load of surface runoff is of such environmental concern that manure application is regulated at both the state and federal levels. In addition, manure is a costly nutrient source with limited availability. Farmers have turned to supplementary nutrient sources, such as legume cover crops, to supply the needed N without adding excessive P to the system. Furthermore, it appears that fields with a long history of manure application have extensive soil reserves of both P and N. The purpose of this research was to determine whether manure applications could be decreased when used in conjunction with legume cover crops, without impacting crop yield. In fields with a history of manure applications, rates can be reduced without negatively impacting corn yield.