New MSU nitrogen recommendation for field corn

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.

Nitrogen plays a significant role in the growth, development and yield of corn. From the mid-1900s until present time, supplemental inputs of nitrogen through various nitrogen sources, especially legumes and manufactured nitrogen fertilizers, have contributed greatly to improvement in corn yields in Michigan. The first increments of nitrogen additions result in large increases in grain yield, but with each succeeding increment added the increase in grain yield becomes less until no further increase in yield occurs from additional nitrogen. The nitrogen recommendation for corn is based on this principle.

Many field studies have been conducted over the years to establish the nature of the relationship between corn grain yield and nitrogen addition. For many years, MSU’s nitrogen recommendations for corn were provided in tabular form based on the yield potential of the soil. More was recommended for soils with higher yield potentials. Studies indicated that, on average, 1.1 to 1.2 pounds of nitrogen was required to produce one bushel of corn. In the 1970s, the tabular information was used to create a linear nitrogen recommendation equation based on yield potential. This equation indicates that the amount of nitrogen required is related to the yield potential of the soil. However, the equation may give the mistaken impression that yield can be increased without limit by applying more nitrogen. This relation only applies within the bounds of the yield potential of the soil.

Corn yield response data collected over the last 10 years show that new corn hybrids are more effective in utilizing nitrogen for producing grain. One bushel of corn is being produced, on average, with 0.8 lb of nitogen. Summarization of corn yield response to data in Michigan and other North Central corn producing states shows that the economic optimum nitrogen rate (EONR) is similar across a range of yield potentials. Many states have now adopted the maximum return to nitrogen (MRTN) approach to determine the appropriate amount of nitrogen to apply for corn. The cost of nitrogen increases linearly with rate whereas the increase in corn grain yield plateaus (Figure 1). Where the difference between the two lines is greatest is the MRTN nitrogen rate. The MRTN nitrogen rate is higher for corn after corn than for corn after soybeans, due to nitrogen benefit from the soybeans. The MRTN rate will also vary with the productivity or yield potential of the soil. The recommended amount of nitrogen varies with the nitrogen-to-corn price ratio. At a nitrogen-to-corn price ratio of 0.10, the MRTN for corn after soybean in Michigan and Minnesota is near 100 and 115 lbs nitrogen/a for medium/low productivity soils and high productivity soils, respectively. In Wisconsin, the similar values are 60 and 115 lbs nitrogen/a. For corn following corn, the nitrogen recommendations are near 135 and 150 for Michigan and Minnesota. For Wisconsin, the recommendations are 105 for medium/low productivity soils and 135 for high productivity soils. The range of nitrogen recommendation for ± $1.00 of the MRTN is approximately ± 15 lbs nitrogen /acre. As the nitrogen-to-corn price ratio increases, the MRTN recommended nitrogen rate decreases.

Suggested nitrogen rates for corn grown in Michigan based on recent nitrogen response data and using the MRTN approach are given in Table 1. The more productive soils have soil conditions that are more favorable for root development and mineralization of nitrogen. Hence, higher yields can be attained in high productivity soils with only slightly more nitrogen fertilizer than in low to medium productive soils. These recommendations are significantly lower than previous nitrogen recommendations. Farmers may be hesitant to make a complete shift to these recommendations, but rather moderate their nitrogen rates based on a better nitrogen efficiency of new corn hybrids (0.8 lbs N/bu than the previous 1.1). To test the new recommendations, farmers should put in strips with the new nitrogen recommendation in comparison to their standard rate and compare yields and economic return. Research data indicates there is very good confidence the new recommendations will provide the best economic return on investment in nitrogen.

Figure 1.  Illustration of maximum return to nitrogen (MRTN) concept. This example uses nitrogen
priced at 40 cent/lb and corn at $4.00 per bushel.

Table 1. Suggested N rates for corn grown in Michigan based on the MRTN approach. 2008.
Table 1

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