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Alternative Benchmarks for Economically Optimal Rates of Nitrogen Fertilization for Corn

^a Iowa Soybean Assoc., 4554 114th St., Urbandale, IA 50322
^b Dep. of Agronomy, Iowa State Univ., Ames, IA 50010
^c Dep. of Plant Science, Univ. of Connecticut, Storrs, CT 06269

^* Corresponding author (pkyveryga{at}iasoybeans.com)

Received for publication November 26, 2006. Discussions of N fertilizer needs for corn (Zea mays L.) usually are based on the assumption that economic optimum rates (EORs) of N provide the best benchmark to indicate the rates most likely to maximize profits for producers. We describe methods for calculating some additional benchmarks and illustrate how efforts to improve N management could be advanced by recognizing several alternative benchmarks simultaneously. We analyzed data from 54 small-plot trials with a new procedure that disaggregates problems associated with systematic model bias and variability in crop yield responses to fertilizer N. We compared the commonly used method for calculating EORs to a method that is described as discrete marginal analysis at near-optimal rates of N fertilization. We described methods for calculating the incremental break-even rate, the incremental rate that gives no crop response, and the incremental rate of N that gives the desired level of profit. Discussions of the relative merits of each benchmark suggest that problems associated with calculating and using the concept of EORs can be avoided by presenting the alternative benchmarks as proposed in this paper.

Abbreviations: EOR, economic optimum rate • EXP, exponential model • IRBE, incremental break-even rate • IRDP, incremental rate that gives the desired level of profit • IRNR, incremental rate that gives no yield response • LRP, linear response and plateau model • QRP, quadratic response and plateau model • QUAD, quadratic model; SR, square root model

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