There are advantages and disadvantages for each method of preplant nitrogen (N) fertilization. Fertilization method and application timing should be evaluated to minimize N loss along with fertilizer cost while meeting crop needs.
Each N fertilizer has a potential for loss and understanding these loss mechanisms can help make a knowledgeable choice for each unique situation.
Denitrification, leaching, and volatilization are three processes that can lead to N loss associated with a preplant application.
Potential Nitrogen Loss
Nitrogen Application Timing
Timing of N application can be influenced by factors such as weather and workload. Applying N at the time of rapid uptake, between V12 and V18 growth stages, can help reduce potential N loss. For more information click below
Nitrogen Sources and Application
Ammonium and nitrate are the two forms of N used by plants. Other forms of N must be converted by soil organisms to one of these forms. The N source should be considered when determining application method. Anhydrous is the densest nitrogen source. All other nitrogen fertilizer sources are made from anhydrous ammonia. These additional manufacturing processes reduce the concentration and typically increase the cost per unit of N. While these lower N fertilizers generally have a higher price per pound of N, this can be affected by seasonal supply and demand. All N sources are generally easier to store and apply, as well as safer to handle than anhydrous ammonia.
Determining the Nitrogen Application Rate
The rate of N applied is an important variable because of economic and environmental issues.
Before determining the amount of N to apply the producer must:
- Estimate the amount of N in the soil that will be available for corn crop use.
- Determine the total N needed for the expected crop yield. As yield goals increase, the amount of N required will also increase.
Determining the proper N rate can be difficult due to temperature and precipitation affecting the release of N (mineralization) from the soil over time and the potential loss of N after an application.
Crop need and corresponding N applications must be calculated every year and for every field. A common calculation to determine the total N needed for an acre of corn can be determined by multiplying the yield goal for the projected crop year by a factor of 1.0 to 1.2 pounds of N per bushel per acre. Applying N based upon yield goals and soil test levels has been a common method used in western corn growing areas to recommend the amount of N to apply. Several universities in the Corn Belt recommend using a “maximum return to N” (MRTN) formula to determine N fertilizer rate. Calculations are made for a single N cost and corn price combination; different price combinations can be placed on the same graph to compare additional N cost and corn price combinations. Different states and different crop rotations are used to formulate different MRTN graphs for those situations. For more information, see the Corn Nitrogen Rate Calculator from Iowa State University at http://cnrc.agron.iastate.edu/.
Microbial activity releases more N under good corn growing conditions. Using variable rate technology to apply more N in fields or areas of fields, where there is greater potential for response, can increase yield potential. Consider all N sources when deciding on which application options to use. Take into consideration a previous legume crop and manure application, where applicable, to calculate the amount of N supplied from those sources and credit it accordingly, to reduce the amount of nitrogen fertilizer needed.
Scharf, P. and Lory, J. 2006. Best management practices for nitrogen fertilizer in Missouri. MU Extension. University of Missouri-Columbia. http://extension.missouri.edu/p/IPM1027.
Nowatzki, J. Endres, G. DeJong-Hughes, J. and Aakre, D. 2017. Strip till for Field Crop Production. AE1370.
North Dakota State University Extension Service. https://www.ag.ndsu.edu/publications/crops/strip-till-for-field-crop-production
Sawyer J., 2021. Corn Nitrogen rate Calculator. Iowa State University Agronomy and Extension Outreach
Web sources verified 1/21/21. 2010_S1