The available nitrogen, phosphorus, potassium and secondary nutrients can vary within a field and definitely will be different from year to year. More nitrogen will be available if the fall-planted crop immediately follows the legume. On sandy soils and in years with normally high precipitation, less nitrogen will be available to spring-planted crops. When selecting target fields, also pay special attention to possible phosphorus movement. Such nutrient-sensitive areas, where phosphorus could move off the site to contaminate surface waters, require conservation methods that minimize soil and nutrient runoff.
Potential solutions are grass borders, grass waterways, contour planting and reduced tillage.
On the other hand, mineral soils limit phosphorus leaching and should therefore not jeopardize groundwater. Nitrogen demand usually determines the application rate. If your soils are only capable of producing 75 bushels of corn per acre, it's wasteful and potentially harmful to the environment to supply nitrogen for 200 bushels per acre. Don't overlook the impact of soil pH from frequent manure applications. Proper soil pH is required to promote organic matter decomposition, improve yields and ensure nutrient availability.