Fertilizer N rate recommendations
N rate guidelines
Minnesota N rate guidelines are based on soil productivity, economics and previous crop. Review how the maximum return to nitrogen (MRTN) guidelines were developed.
Working with the MRTN guidelines
Selecting the optimum nitrogen rate is important for maximizing profitability and minimizing environmental risks. The goal is to hit the economic optimum N rate, that point where the last bit of fertilizer is paid for by the final yield gain. Fluctuating fertilizer costs and corn prices affect this N rate. To calculate your N cost per pound, use the fertilizer cost per ton in the following equations:
Urea ($/ton) / 920 = N cost in $/pound
Anhydrous ammonia ($/ton) / 1640 = N cost in $/pound
Once you've calculated your N cost in $/pound, calculate the N cost/N price ratio using your N price. For example, if anhydrous ammonia costs $600/ton, the N cost per pound is $0.36. If the corn price is $4.00 per bushel, the ratio calculation is:
$0.36 / $4.00 = 0.091
Compare the calculated ratio with those in Table 1 and choose the closest one. In this case, 0.10 would be the best selection. For corn following corn, the MRTN is 165 pounds N per acre and acceptable range is 152-180 lb N/acre.
Table 1. Guidelines for use of nitrogen fertilizer for corn grown following corn or soybean when no irrigation is used.
