Nitrogen recommendations based on yield goals require reliable estimates of the factors affecting corn (Zea mays L.) N needs. If these parameters are unknown or erroneously estimated, N recommendations may be inappropriate from economic and environmental perspectives. This study was conducted to develop corn N recommendations using soil‐specific data from 117 corn N response experiments and to compare these recommendations with those based on yield goals. Soil‐specific recommendations for six major soil regions in Wisconsin were developed using a response function based on combined data from all experiments conducted on a specific soil, and from response surface models containing N rate and residual nitrate‐N variables. Yield goal‐based recommendations were generated with a widely used mass balance approach. Recommendations based on response data provide a constant N rate across a wide range of actual yields consistent with the observation that economic optimum N rates on a specific soil do not change with yield. Where yield goals are based on a multiyear average of attained yields on a given soil, N recommendations are the same as those derived from soil‐specific response data. Where yield goals are much higher or lower than the average of attained yields, however, inappropriate N recommendations are obtained. Although recommendations based on response data require an adequate database for each soil, grouping of soils with similar N response characteristics is possible and minimizes the need for N response data from individual soils. Our research shows that optimum N rates are less variable than yields, indicating that a relatively small database for a representative soil should provide enough information to make sound N fertilizer recommendations. Economic returns from N use calculated for a typical range of corn/N price ratios (16.7 to 10.0 lb N/bu) show that it is usually not profitable to increase or decrease the soil‐specific N rate recommendation. A base N rate derived from yield response data with annual adjustments for soil nitrate‐N has the advantage of providing a very site‐specific N recommendation while avoiding excessive or unprofitable N rates due to selection of unrealistic yield goals.
Research Question
Expected yield or yield goal is the primary management input used to develop corn N recommendations in most of the USA. Although many N response studies have been conducted on the major soils used for corn production, current yield goal‐based N recommendations do not reflect the typical pattern of corn response to applied N. Since N response data provide soil‐specific information on corn N needs, recommendations based on these data could help to minimize excess N applications due to selection of unrealistic yield goals and ensure profitable use of fertilizer N. The objectives of this work were to develop corn N recommendations based on soil specific data from numerous N response experiments and to compare these recommendations with those based on yield goal.
Literature Summary
Inappropriate N appl...
