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 Agronomic Optimum N Rate (AONR) represents the total amount of fertilizer N (including starter N) required to maximize yield, but not necessarily profit. The AONR varied among regions of the state from about 210 to 263 lbs N / ac, depending partly on soil organic matter and soil drainage characteristics.
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) are defined as those that maximize dollar return from the nitrogen fertilizer investment. Because the yield benefits from additional N decrease as N rates approach the AONR, the EONR will almost always be less than the AONR. The EONR in our trials varied throughout the state from about 170 to about 210 lbs N / ac. Region-specific EONR, calculated for various combinations of N fertilizer cost and grain price, are listed in the accompanying tables.
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