Adaptive Management to Improve Nitrogen Recommendations for Corn.

Most of the N available to corn is released from soil organic matter by biological processes. Biological processes are particularly difficult to predict and impossible to control on a field-scale. Effective management of biological processes, however, is possible using an adaptive approach to the management. Adaptive management of biological processes is based on post-mortem evaluation of predictions of biological processes. Current N recommendations for corn use yield to predict the amount of N available to corn from biological processes occurring in soils during the growing season. Our current recommendation system, however, does not evaluate these predictions of available N, and therefore, our N recommendations do not improve with time. Farmers often use yield or the greenness of corn to informally evaluate N availability, but no systemic post-mortem evaluation of our N recommendations is performed to improve N recommendations. The cornstalk nitrate test (CSNT) provides post-mortem evaluations of N recommendations. Results from the CSNT show N availability during the growing season from a relatively large volume of soil. A decision support system for using the CSNT to improve N recommendations is being developed for Iowa and for the Chesapeake Bay area. Field history and CSNT values are used to modify current N recommendations. Results have shown that current N recommendations: 1) often are too low in a corn silage-rye silage system, 2) need to be adjusted for the timing and form of N, and 3) often do not accurately predict the amount of N available from manure. Use of adaptive management will increase the efficiency of N use in corn.