Adapting to the new corn nitrogen recommendations
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
The change from recommending nitrogen (N) based on expected yield to recommending N based on economic return is quite significant. To adapt to this change will take time and some on-farm N rate evaluation by farmers to become comfortable with these new recommendations. In making this change, farmers may want to use the higher recommended amount in the “Maximum Return to N (MRTN)” range in Table 1. For example, if the five-year running average year is 170 bushels per acre, the previous crop was corn and the N:corn price ratio is near 0.10 ($0.50/ lb N and $5.00/ bu corn), then the recommended N rate is 150 lbs N/acre. The upper range value is 165 lb N/acre. If soybean is the previous crop, the upper range value is 130 lb N/acre.
To determine the MRTN rate from Table 1, you need to know: 1) the productive capacity of the soil, 2) the previous crop, and 3) the N:corn price ratio. The N:corn price ratio is the cost of N ($/lb) divided by the expected corn selling price ($/bu). For example, if the price of N is $0.50/lb ($820/ton anhydrous ammonia) and corn is $5.00/bu the N:corn price ratio is 0.10 (0.50/5). If the price of N is $0.65/lb ($600/ton urea) and corn is $5.00/bu, then the N:corn price ratio is 0.13 (0.65/5).
If the previous crop is something other than corn or soybean, use the recommendations associated with soybeans. Any crop other than corn as the previous crop will usually result in some N benefit similar to soybean. When the previous crop is alfalfa or clover, then some additional N credit can be taken based on percent stand. For established alfalfa the additional N credit will be approximately equal to percent stand. For clovers, the additional N credit will be about 0.5 x percent stand.