Ammonia Volatilization and Soil Nitrogen Changes after Urea and Ammonium Nitrate Fertilization of Pinus Taeda L.

Abstract

AbstractFrom 3.9 to 13.1% of the nitrogen (N) was lost to the atmosphere when 200 kg/ha of N as (NH2)2CO were applied to an undisturbed forest soil during each of the four annual seasons. There were no measurable losses from a comparable NH4NO3 treatment. The majority of the loss occurred within the first 2 weeks after fertilizer application. During this time volatilization of NH3 from the (NH2)2CO‐amended soils appeared to depend more on moisture in the soil and time and amount of precipitation after fertilizer application than on season of fertilizer application. Conditions of light precipitation providing adequate moisture for (NH2)2CO hydrolysis but insufficient to leach the (NH2)2CO resulted in the greatest NH3 losses. Heavy precipitation leached the urea or NH3 deeper into the soil profile where it was retained. Although differences were not significant among seasons, winter loss < fall < summer ≃ spring. Precipitation trends and seasonal temperature differences may be responsible for these differences.Ammonium‐N from (NH2)2CO remained in the forest floor and top few centimeters of mineral soil. In contrast, the NH4+ produced by the ionization of NH4NO3 was carried deeper into the soil profile.