By Andi Anderson
As Illinois farmers complete harvest and prepare for fall fertilizer applications, nitrogen management deserves careful attention. According to Torey Colburn, Midwest Conservation Agronomist at American Farmland Trust, producers should prioritize field conditions rather than follow a fixed calendar when applying anhydrous ammonia.
Fall applications can help distribute farm workloads and take advantage of favorable fertilizer prices. However, applying nitrogen several months before crops need it increases the possibility of nutrient losses through leaching and denitrification.
When anhydrous ammonia (NH3) enters the soil, it reacts with water and converts into ammonium (NH4+). This positively charged form attaches to soil particles and organic matter, reducing its movement through the soil.
Soil microorganisms gradually transform ammonium into nitrate (NO3-) through nitrification. Unlike ammonium, nitrate moves easily with water and can enter tile drainage systems. In saturated soils, it can also be converted into gases through denitrification.
Soil temperature plays an important role in controlling this process. Nitrification slows considerably when soil temperatures remain below 50 degrees Fahrenheit.
Therefore, Illinois producers are generally advised to wait until temperatures fall below 50 degrees at a 4-inch depth, measured around 10 a.m. in bare soil. Waiting until temperatures reach 40 degrees would provide additional protection when practical.
Managing Nitrogen Losses
Nitrification inhibitors such as N-Serve (nitrapyrin) can help reduce nitrogen losses by slowing the conversion of ammonium into nitrate. However, these products do not completely stop nitrification or protect nitrogen that has already become nitrate.
Proper application remains essential. Dry, cloddy soil conditions can prevent injection slots from sealing properly, allowing ammonia to escape. Adequate application depth, placement, and moisture conditions are necessary for effective nitrogen management.
A 2024 study by Lowell Gentry and colleagues examined nitrogen management systems in a tile-drained corn-soybean rotation in central Illinois between 2016 and 2019.
Researchers found that fall-applied anhydrous ammonia with N-Serve resulted in cumulative nitrate-nitrogen losses of 103 pounds per acre through tile drainage. A spring split-application system combined with cereal rye cover crops recorded approximately 58 pounds per acre, representing a 43% reduction.
The findings compared complete management systems rather than isolating N-Serve's effectiveness.
Making Better Fertilizer Decisions
Colburn emphasizes that successful nitrogen management involves more than completing fertilizer applications before winter. Producers must consider application timing, placement, rates, and available management tools.
Keeping nitrogen in the soil until crops can absorb it helps protect fertilizer investments while reducing potential water quality impacts.
N-Serve can provide additional protection, but it should not replace proper application timing and field management. Ultimately, farmers should evaluate soil conditions and weather forecasts before applying fall nitrogen to minimize avoidable nutrient losses.
Photo Credit: pexels-jan-kroon
Categories: Illinois, Crops, General