Nitrogen moves readily in the soil and applying all the N needs at seeding time is not only risky but may not be the most efficient strategy or practice. Here are the ways that we can lose nitrogen.
Immobilization - Immobilization refers to the process in which nitrate and ammonium are taken up by soil organisms and therefore become unavailable to crops. Immobilization occurs when decomposing organic matter contains low amounts of nitrogen and those soil microbes out compete plants for that N. It is the reverse of mineralization, where N becomes available to plants.
Leaching – As N moves readily in the soil, N, in the nitrate form, can be lost to leaching and these losses can be significant. For a 1” rain event early in the growing season you could potentially lose up to 50% of the spring or fall applied N. In sandy soil the N can move 7 to 10 inches below the root zone, 5 inches in loam and 3 inches in a clay loam soil.
Volatilization – Volatilization is the loss of N through the conversion of ammonium to ammonia gas, which is released to the atmosphere. The volatilization losses increase at higher soil pH and conditions that favor evaporation (e.g. hot and windy). The process of ammonia volatilization commonly takes place when nitrogen is in an organic form known as urea. A big issue for anyone that melts urea and sprays that on your crop in a foliar application.
Denitrification - Denitrification is the process that converts nitrate to nitrogen gas, thus removing bioavailable nitrogen and returning it to the atmosphere. Denitrification occurs when N is lost through the conversion of nitrate to gaseous forms of N, such as nitric oxide, nitrous oxide and dinitrogen gas. This occurs when the soil is saturated and the bacteria use nitrate as an oxygen source.
