October 13, 2014 – There has been a large change in corn grain prices this fall. How might that affect recommended nitrogen (N) fertilizer or manure-N application rates, and planning for the 2015 crop? The answer depends on more than just the price of corn, but also the price of nitrogen. It is the ratio of these prices (price ratio, where the $/lb actual N is divided by the $/bu corn; example, $0.50/lb N and $3.50/bu corn is a 0.14 price ratio). Both prices are important and influence recommended N rates as the ratio reflects the last unit of N that can be paid for by the yield increase from that N application. In Iowa, recommended rates (Maximum Return to N, MRTN) come from the Corn Nitrogen Rate Calculator (CNRC), which is the online tool providing rate recommendations for corn following corn and corn following soybean. The rates derived from the CNRC are adjusted for user specified N and grain prices. While a significant change in grain price may be troublesome, it may or may not affect recommended rates because of current N price.
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