2012 MSU corn nitrogen recommendations

Recent volatility in both the grain and fertilizer markets may warrant a second look at nitrogen rates.

Though some spring planting got off to an early start, the recent prolonged period of sub-freezing nighttime temperatures has delayed some planting around the state. With May around the corner, growers may want to ensure that their pre-plant or sidedress nitrogen application rates result in the most profitable rate of return. Corn prices have fallen 3 to 4 percent over the last four weeks (as of April 26, 2012), while bulk urea prices have risen close to 25 percent over a similar time period, meaning what may have been the Maximum Return to Nitrogen (MRTN) recommendation earlier this spring may no longer be the case.

Both the MRTN recommendations and on-line corn nitrogen calculator have been updated for first time in four years.

The MRTN system was adopted to further enhance farm profitability by maximizing the economic return of nitrogen fertilizer invested while simultaneously addressing some of the negative environmental consequences that occur when applying excessive nitrogen rates. 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. Several nitrogen:corn price ratios were built into the recommendation system. The “Corn Nitrogen Rate Calculator” is a web-based tool to help determine nitrogen application rates.

Changes in 2012

Three important notes about the 2012 MRTN recommendations:

  1. Corn yield increases over the last several years have resulted in a reclassification of the soil productivity potentials to more accurately represent growers’ yield potential. This adjustment resulted in a 10 to 15 bushel increase across the low, medium, high, and very high categories from previous years.
  2. 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.
  3. When the previous crop is soybean, the nitrogen credit is built into the recommendation. Do not take any additional nitrogen credit as the rotational effect of soybean is already accounted for in the MRTN guidelines.

Table 1. Suggested N rates for corn grain grown in Michigan at several nitrogen:corn price ratios, 2012.

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

170

155-1852

150

135-165

135

125-150

120

110-135

Soybean3 and

small grains4

145

130-160

120

110-135

105

95-120

95

85-110

Medium/Low

Corn

140

130-155

130

120-145

120

110-135

105

95-120

Soybean3 and

small grains4

115

100-130

95

85-110

85

75-100

75

65-90

Loamy Sands and Sands

(CEC   < 8.0)

Irrigated – all crops

210

195-225

190

175-205

175

160-190

165

150-180

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.

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