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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

View larger version (18K): [in this window] [in a new window]   Fig. 1. Relationships between corn grain yields and rates of N fertilization for three crop categories analyzed.

View larger version (21K): [in this window] [in a new window]   Fig. 2. Discrete marginal products (DMPs) of N fertilization for the incremental increases in rates of N fertilization applied for three crop categories.

View larger version (25K): [in this window] [in a new window]   Fig. 3. Marginal products (MPs) of N fertilization as calculated from five different models for all rates and for rates in the near-optimal range (inserts A, B, and C). EXP, exponential model; LRP, linear response and plateau model; QRP, quadratic response and plateau model; QUAD, quadratic model; SR, square root model.

View larger version (17K): [in this window] [in a new window]   Fig. 4. The second derivatives of continuous models used to describe the relationship between rates of N fertilization and grain yields. EXP, exponential model; QUAD, quadratic model; SR, square root model.

View larger version (17K): [in this window] [in a new window]   Fig. 5. Effects of fertilizer-to-grain price ratios on economic optimum rates (EORs) as calculated from five different models used to describe relationships between rates of N fertilization and grain yields.

View larger version (17K): [in this window] [in a new window]   Fig. 6. Relationships between discrete marginal products (DMPs) of N fertilization and N rates in the near-optimal range when all observations are included in the analysis.

View larger version (21K): [in this window] [in a new window]   Fig. 7. Discrete marginal products (DMPs) of N fertilization calculated for three incremental increases in rates of N fertilization in the near-optimal range for each crop category.