But we also found that a relatively small percentage of the farmers contributed disproportionately to the excess nutrient applications. For example, most of the farmers surveyed would, on average, apply about 160 pounds of nitrogen per acre. The situation with phosphorus is similar. The study also shows that most of the excess nutrients on cornfields come from manure spread there. Shepard sees several possible reasons for the failure to credit the manure properly.
Farmers face engineering limitations.
The box-style manure spreader widely used across the state is designed to get rid of a waste rather than manage a valuable nutrient source. Most water protection programs have emphasized building expensive manure storage structures while failing to emphasize the crediting behaviors needed to manage the manure stored in those structures. Fertilizer dealers make recommendations while underestimating manure applications because of uncertainties about the type, amount and evenness of its distribution. Although farmers recognize manure's value as a soil amendment, they find it difficult to act on this knowledge because of their farm work schedules. What remains are the complex and difficult challenges of changing agronomic behavior, farmer by farmer, one at a time.