Several methods can help estimate nitrogen (N) loss and supplement N need. They should be used as guides and for information regarding N application. Late spring soil nitrate test. Details about this test can be found in the Iowa State University publication PM 1714, Nitrogen Fertilizer Recommendations for Corn in Iowa. Soil condition should allow the collection ofgood samples from the entire one-foot depth.
Available at: http://works.bepress.com/john-sawyer/25/