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Corn Nitrogen Recommendations

By Kurt Steinke

Variable—the one word often used to describe corn response to nitrogen (N). Soil variability within a field influences the N supply due to changes in soil texture, organic matter content and topography while environmentally both temperature and rainfall distribution are often key drivers of N variability across entire landscapes. Despite new application technologies and a plethora of products targeting improved plant growth and efficiency, three factors including rainfall frequency, crop heat units and soil texture still appear to offer the greatest influence on corn response to N.

Resources are available to reduce grower uncertainty when selecting corn N rates. Seven states through the Corn Belt, including Michigan, utilize the Maximum Return to Nitrogen (MRTN) corn N recommendation system. The MRTN model 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 model provides a range of N rate recommendations based on corn yield response to N over many years and across a range of Michigan soils. What the MRTN model also recognizes and accounts for is that the most economically optimum nitrogen rate will never be constant as corn and fertilizer prices fluctuate over time. The model provides a profitable range of N rates that allows for user input to adjust rate based on crop rotation, soil productivity potential and current price of N fertilizer and corn grain.