Nitrogen Accounting and Credits

Efficient nitrogen fertilizer use requires that the producer give proper credit for non-fertilizer nitrogen sources before determining the nitrogen rate. Significant nitrogen sources include soil organic material and soil residual nitrate (determined by soil sampling), manure and organic materials (determined by analyzing a sample of the material), legumes (determined according to the previous crop), and irrigation water (determined by testing irrigation water). Actual nitrogen credits from these sources can vary widely, but in many cases the nitrogen fertilizer rate can be reduced significantly after accounting for these credits. More information on nitrogen accounting is available in the resources listed at the end of this chapter.