If applied N or mineralized organic matter N (conversion from organic to ammonium) would stay in the ammonium (NH4+) form, then losses would not occur because ammonium attaches to soil and does not leach (move through the soil with water) or denitrify (microbial conversion to N gases when soils become saturated). Unfortunately, that isn’t the way it works. Ammonium is converted to nitrate (NO3-) via nitrification. Nitrate is the form that can be moved out of the soil profile by leaching or lost by denitrification. The conversion of ammonium to nitrate and the conversion of nitrate to N gases are both microbial processes. Hence, potential N loss is dependent upon factors that influence each – for nitrification soil temperature is very important (faster with warm soils, slower with cold soils); for denitrification soil temperature, soil moisture (only occurs when soils are saturated – anaerobic conditions) and readily available organic matter for an energy source. If fertilizer N is applied in the nitrate form, then that N is immediately subject to these loss pathways. Mineralization does occur when soils are saturated, so ammonium can accumulate in flooded soil and add to crop available N.
Iowa State University
Sawyer, John E., "Relationship of Nitrogen Conversion in Soil to N Loss" (2010). Integrated Crop Management News. 446.
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