Fertilizer N rate recommendations

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.