Loss of Nitrogen by Ammonia Volatilization and Denitrification After Application of Urea to Maize in Shanxi Province, China.

Because of concern that emission of nitric oxides (NO_x) and ammonia (NH₃) from agriculture may form secondary aerosols in the atmosphere and impact on the variability and intensity of the Asian Monsoon we determined the importance of emission of these gases from a maize crop fertilized with urea in northern China. The fertilizer was deep placed by traditional farmers’ practice and emission of NO_x and NH₃ was determined with a backward Lagrangian stochastic dispersion technique. The emission measurements indicate that 1.2 % of the applied nitrogen (N) was lost as NO_x. This loss is far greater than the fertilizer derived emission of NO_x derived by others and it is suggested that this is because the measurements were made continuously rather than as spot measurements with static chambers. The results for NH₃ show that even though the fertilizer was placed below the soil surface a small amount (6.5 % of the applied N) was still lost to the atmosphere. Soil analyses to depth indicate that little nitrate was leached down the profile and a study using soil cores and acetylene inhibition to measure denitrifying activity suggested that the rate of denitrification was very slow in this soil until heavy rain fell 10 days after fertilizer application. The results suggest that in this soil with a slow denitrification rate and little leaching, deep placement of the urea to limit NH₃ volatilization is an effective method for decreasing N loss to the atmosphere and increasing fertilizer use efficiency.