Integrated Crop Management News

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Corn N fertilization. I am often asked what N rate should be applied for corn production. I hesitate to give too simple of an answer, but actually a straightforward rate of 125 lb N/acre for corn following soybean (SC) and 175 lb N/acre for corn following corn (CC) (continuous, second-, or third-year) with good N management works well. If you have followed Iowa State University Extension publications regarding N management over the years, these rates are in the middle of suggested rate ranges provided since at least 1979 (100–150 lb N/acre for SC and 150–200 lb N/acre for CC). An analysis of recent data from many N rate trials conducted in Iowa since 1991 indicates these “straightforward” rates are still correct. Figure 1 shows the economic net return to N for SC and CC at four different price ratios of N price:corn grain price ($/lb N:$/bu corn grain). For the figure, the corn price was held constant at $2.20/bu and N prices were varied from $0.11, 0.22, 0.33, and 0.44 per lb N. These give price ratios of 0.05, 0.10, 0.15, and 0.20, respectively at the four N prices. The point of maximum return to N (MRTN) is the N rate where the greatest economic net return to N occurs. This is indicated by the solid symbols on each price ratio line. As you can see, at the 0.10 price ratio the maximum return occurs at 123 lb N/acre for SC and 174 lb N/acre for CC, at the middle of currently suggested N rate ranges.



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