IS YIELD RESPONSE SITE-SPECIFIC? REVISITING NITROGEN RECOMMENDATIONS ON CORN

Variable rate application (VRA) of fertilizer to U.S. cereal crops has provided uneven profitability results. Typically, yield response is negligible and input costs savings are insufficient to cover the added information and equipment costs of the technology. Largely overlooked has been the possibility that typical state-level fertilizer recommendations might be unsuited to VRA management. This research uses experimental data from 1999-2001 on 14 farm fields in south-central Michigan to test the hypothesis that site characteristics interact with nitrogen in affecting corn yield. Included among the site characteristics are a) soil test data, b) soil electrical conductivity, and c) terrain traits (potential wetness and insolation indexes). Site characteristics were found to interact significantly with nitrogen in affecting corn yield response in all three years. The difference in gross margins between VRA using site-characteristic based recommendations and uniform fertilizer application using whole-field or state-level recommendations was not enough to cover the cost of soil testing and VRA for most fields and years at current fertilizer and corn prices. Given that the costs of implementing VRA fertilization could not be recovered, few growers are likely to be willing to pay the added costs of experimentation and data analysis to develop site-specific recommendations, at least under conditions like those evaluated here