This report summarizes corn yield response to fertilizer nitrogen (N) rate in field-scale trials conducted around the state of Indiana since 2006.
These results are applicable to N management programs that use efficient methods and timings of N fertilizer application. The average Agronomic Optimum N Rate (AONR) for corn/soy in 53 trials conducted on medium- and fine-textured soils in southwest, southcentral, southeast, and westcentral Indiana was 208 lbs N/ac. The average AONR for 30 trials conducted on medium- and fine-textured soils in northwest and northcentral Indiana was 212 lbs N/ac. The average AONR for trials conducted on medium- and fine-textured soils in other regions of the state were 232, 251, and 263 lbs N/ac for central (23 trials), east central (26 trials), and northeast (11 trials) Indiana, respectively. The average AONR for 16 trials on non-irrigated sandy soils was 202 lbs N/ac. At five Purdue Ag. Centers where we conducted paired trials of corn following soybean (corn/soy) and corn following corn (corn/corn) from 2007 to 2010, the average AONR for corn/corn was 44 lbs greater than for corn/soy while average corn/corn yields were 18 bu/ac less than the corn/soy yields.
Economic Optimum N Rates (EONR) calculated for various combinations of N fertilizer cost and grain price are listed in Tables 2-7 for regions of the state.
Nitrogen fertilizer is one of the significant variable production costs for corn. Applying "more than enough N" is no longer cheap "insrance" as it once was many years ago. Applying "more than enough N" is also not environmentally friendly. High N fertilizer costs and environmental impacts should encourage growers to critically evaluate their N management program, including application rate, fertilizer material, and timing.