Maximizing return on corn nitrogen investments

Several consecutive years of volatile spring weather and lower crop prices may bring uncertainty when selecting corn nitrogen recommendations.

Cold, hot, dry, wet, early, late; Six words that both summarize and demonstrate the variability in spring planting conditions for the last several Michigan cropping seasons. Though uncertainty with spring weather may always exist, resources are available to reduce grower uncertainty when selecting corn nitrogen (N) rate applications. Seven states through the Corn Belt, including Michigan, have adopted the Maximum Return to Nitrogen (MRTN) corn N recommendation system.

The MRTN system was adopted to further enhance farm profitability by maximizing the economic return of N fertilizer invested while simultaneously addressing some of the negative environmental consequences that occur when applying excessive N rates. The system provides a range of N rate recommendations based on many years of corn yield data from N response trials conducted exclusively across a range of Michigan soils. What the MRTN system also recognizes and accounts for is that the most economically optimum nitrogen rate will never be a constant measure as both corn and fertilizer prices will fluctuate over time. The system provides a profitable range of N rates that allows for user input to adjust N rates based on crop rotation, soil productivity potential and current price of N fertilizer and corn grain.

The MRTN recommendation table is a summary of results from the Michigan database within the Corn Nitrogen Rate Calculator. Both tools may be accessed via the Soil Fertility and Nutrient Management Program website at Michigan State University.

Suggested N rates for corn grain grown in Michigan at several nitrogen:corn price ratios, 2015

Soil productivity potential1

Previous crop

N:Corn price ratio

0.05

0.10

0.15

0.20

Suggested N Rate (lbs. N/acre)

High/Very high

Corn

175
160-1902

155
140-170

140
130-155

125
115-140

Soybean3 and small grains4

150
135-165

125
115-140

110
100-125

100
90-115

Medium/low

Corn

145
135-160

135
125-150

125
115-140

110
100-125

Soybean3 and small grains4

120
105-135

100
90-115

90
80-105

80
70-95

Loamy sands and sands (CEC < 8.0)

Irrigated – all crops

215
200-230

195
180-210

180
165-195

170
155-185

Copyright 2015 Kurt Steinke, MSU Department of Plant, Soil and Microbial Sciences
1
Low: average yield = < 135 bu/A; Medium: average yield = 136 to 165 bu/A; High: average yield = 166 to 195 bu/A; Very High = more than 196 bu/A; (average yield is the five-year running average disregarding unusual highs and lows). 

2 Range approximates + $1 of the maximum return to N (MRTN) rate.
3 When the previous crop is soybean, the nitrogen credit is built into the recommendation. Do not take any additional nitrogen credit. Nitrogen credits for previously applied manure need to be subtracted from the N recommendations.
4 Refers to small grains interseeded with leguminous cover crop species. Small grains not interseeded with leguminous cover crop species should default to previous crop corn.

Using the MRTN recommendations

Michigan State University Extension recommends following these important notes when using MRTN recommendations.

  • The MRTN system is not an individual site-year recommendation system. Rather the system provides corn N recommendations that have proven profitable over many years, not just one, thus accounting for both optimal and sub-optimal growing seasons. Field-specific circumstances including excessive rainfall after early N applications or individual large rainfall events are not accounted for and may require adjustments to in-season N applications.  
  • Corn yield for the N rates listed at the 0.05 price ratio will be near maximum levels, but N rates for higher price ratios may result in a greater economic return to the grower.
  • When the previous crop is soybean, the N credit is built into the recommendation system. Do not take any additional N credit as the rotational effect of soybean is already accounted for under the “previous crop” heading.
  • If the previous crop was a small grain that was interseeded with a leguminous cover crop species, growers should follow the recommendation category for previous crop soybean and small grain. If no leguminous cover crop was used with the small grain, growers should default to the recommendation category for previous crop corn.
  • The profitable range listed beneath suggested N rates can be used to adjust N rates based on an individual grower’s familiarity with a specific field (i.e., tendency to yield greater or less than expected), the amount of risk a grower wishes to assume, or locally important air, soil and water concerns.  

 Dr. Steinke’s work is funded in part by MSU’s AgBioResearch.     

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