It is well established that much of the nitrogen in manure can be lost as ammonia soon after application, and that the percentages of N lost vary greatly with site conditions. N by these mechanisms helps explain why corn producers consider animal manures to be an unreliable source of N for corn production. Problems caused by variability in losses of plant-available N from manured cornfields were insurmountable in the past, but they can be addressed today. This approach makes it possible to apply N fertilizer only where needed. Details for using this soil test are provided in a new ISU Extension publication, Nitrogen Fertilizer Recommendations for Corn in Iowa , Pm-1714.
Information provided by the soil test has two noteworthy benefits.
First, it will help producers avoid costly applications of unneeded commercial fertilizers after manures are applied. Second, it should help producers select rates and methods of application that make manure a more reliable source of N for corn production. The overall effect should be a substantial net reduction in the amounts of N applied to soils and lost from soils. Only small investments of time and money are needed to use the late-spring test to evaluate current N management practices. Collecting and testing two or three samples from each of three or four fields should provide a reasonable evaluation for most producers.