The profitability of crop production is highly dependent on proper nitrogen (N) management, as N fertilizer represents a large fraction of the total cost of production. Unfortunately, N is the one of the most challenging nutrients to manage in field crops. A primary challenge for farmers is to provide a sufficient quantity of plant available nitrogen (nitrate and/or ammonium) to crops, while minimizing N loss to the environment.
There are inherent tradeoffs and risks with timing of N fertilizer application. Nitrogen should be applied to coincide with crop demand and uptake to the extent possible. Application of N fertilizer before planting simplifies management but poses a greater risk of N loss to the environment. Application of N fertilizer during the growing season minimizes N loss, but adds a new risk of not being able to apply N if soil conditions remain wet for too long. Growers need to balance these tradeoffs and adjust N management based on time, equipment constraints, soil texture, and weather patterns.
The appropriate placement of N fertilizer depends on the type and timing of fertilizer applied. Anhydrous ammonia (AA) must be placed into the soil to capture ammonia. Urea-containing fertilizers should be incorporated into the soil when temperatures are warm but can be left on the soil surface when cold. Banding urea-containing fertilizers and AA slows their conversion to nitrate which can reduce N loss.
Nitrogen fertilizer source trials have consistently shown that numerous N fertilizer forms are effective in providing N nutrition to crops. The choice of fertilizer source should be based on application timing and placement, cost, availability, equipment considerations, and farmer preference.
Indiana, Michigan, and Ohio corn N rate recommendations (and those of Iowa, Illinois, Minnesota, and Wisconsin) are based on extensive N response trials conducted over several years in each state. These trials have determined the N rate at which the last pound of added nitrogen fertilizer returns a yield increase large enough to pay for the cost of the additional fertilizer. This approach, called the maximum return to nitrogen (MRTN), is favored over trying to maximize corn yields because of the economic volatility in both corn grain and nitrogen fertilizer prices.
Calculating the MRTN requires 4 inputs: 1) location, 2) the previous crop grown (corn; soybean or small grain), 3) price of nitrogen fertilizer, and 4) price expected per bushel of corn. When corn prices are low and/or fertilizer prices are high, nitrogen rates are reduced; when corn prices rise or N fertilizer prices fall, recommended nitrogen rates increase. The corn N rate recommendations do not account for N fertilizer application timing, but rather assume best management practices are used. Therefore, the recommended N fertilizer rate represents the total N to be applied over the growing season, regardless of timing of N application.
The corn N rate calculator at cnrc.agron.iastate.edu provides both a single recommended N rate and also a Profitable N Rate Range, that is, a range of N fertilizer rates predicted to produce a profitable return. The simplicity of this tool helps to facilitate the ease of use across each state, but farmers are encouraged to use other available information such as weather, soil type, pre-side-dress N tests, management history, and previous performance to help refine a localized N rate for any given field.
Indiana Corn N Rates
Economically optimal N rate recommendations for corn following soybean differ by region in Indiana. In addition to the calculator website given above, specific recommendations and additional guidelines for Indiana are at agry.purdue.edu/ext/corn/news/timeless/nitrogenmgmt.pdf.
Michigan Corn N Rates
Michigan corn N rate model provides an N rate and profitable range adjustable by growers based upon crop rotation, soil productivity potential, current price of N fertilizer and corn grain, and field history. Corn N rates listed near the 0.05 price ratio will be near maximum production levels but N rates for greater price ratios may result in a greater economic return to the grower. Please see soil.msu.edu for recent updates.
Ohio Corn N Rates
When developing an optimal N fertilizer rate for soft winter wheat, soil texture, organic matter, residual manure or fertilizer contributions, crop rotation, planting date, and yield goal should all be considered.
Tri-State Fertilizer Recommendations for Corn, Soybeans, Wheat, and Alfalfa
Executive Summary | Soil Sampling, Handling, and Testing | Soil pH and Lime Recommendations | Nitrogen | Phosphorus and Potassium | Calcium, Magnesium, and Sulfur | Micronutrients | Additional Resources | Authors and Acknowledgements
This website provides a summarized version of the Tri-State Fertilizer Recommendations, reporting the main points of the document but lacking comprehensive detail. For complete information, please see the full version which is available from The Ohio State University Extension Publications Store.