Spatial and temporal variation in economically optimum nitrogen rate for corn

The economically optimum N rate (EONR) required for corn (Zea mays L.) may vary spatially due to variation in soil characteristics and temporally due to the interactions of environmental factors. The objectives of this research were to quantify the impact of field variability on the yield response of corn to N fertilization and to evaluate the temporal stability of these response functions. A production field near Revere, MN, was cropped with corn in 1995, 1997, and 1999 in rotation with soybean [Glycine mar (L.) Merr.]. Four replications of seven treatments were established in a split-plot arrangement of a randomized complete block design. Main plots consisted of three N rates (0, 67, 134, and 202 kg ha(-1)) while the split plots were two rates (0 and 0.56 kg ha(-1)) of nitrapyrin [2-chloro-6 (trichloromethyl)pyridine]. Each replication was divided into subblocks to estimate spatial patterns in yield N response and EONR. Spatial analysis indicated that only half of the field responded to N. Uniform application recommendation of 145 kg N ha(-1) for the whole field overfertilized these areas while other areas were underfertilized. Variable-rate N applications according to the EONR would have resulted in 69 and 75 kg ha(-1) less N being applied than the uniform N rate in 1997 and 1999, respectively. Potential economic benefits were $8 and $23 ha(-1) higher than the uniform N rate in 1997 and 1999, respectively. Approximately 60% of the field responded in a similar manner in both 1997 and 1999, suggesting that temporal variations must also be considered with site-specific N management.