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Fall Application of Nitrogen
Over the years fall nitrogen application has offered advantages over spring nitrogen applications. Advantages are measured against potential nitrogen loss prior to crop usage. Fall application usually spreads workload during favorable weather when more time is available than a typical spring season. In addition, fall fertilizer is often less expensive and application equipment is more available than in spring time.
Fall application also reduces spring tillage needs usually resulting in a better seedbed which is crucial for high yielding crops. Spring nitrogen application offers advantages in application timing and delaying expenses.
Nitrogen application closer to crop use reduces loss potential to leaching and denitrification processes. Soil incorporated nitrogen applied as NH3 (anhydrous ammonia or urea) needs to be converted to NO3 before losses occur. Time required for conversion depends on soil moisture and soil temperature. Many days to weeks are required for complete conversion of NH3 to NO3. Nitrogen application that occurs when soil temperatures are below 50 degrees F retain most of the nitrogen in a NH3 form until soils warm, usually after small grain planting.
Leaching and denitrification loss requires substantial amounts of precipitation on medium to fine textured soils prevalent in North Dakota.
Most of these soils will hold 9" of plant available water in four feet of soil. Average August 1 to April 1, precipitation is 8" in NE North Dakota.
Areas with soils near field capacity should apply NH3 in mid to late October to minimize potential losses. Dryer soils can have nitrogen applications made earlier without much risk of nitrogen loss.
Sandy textured soils have a high leaching loss potential and nitrogen should only be applied in the spring.
Many times research results show higher or equal yields for fall nitrogen applications as compared to spring applications. Dryer seedbeds and moisture loss from spring incorporation often account for better yields with fall applications. Evaluate each field situation before nitrogen applications.
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