AMMONIA LOSS FROM SOIL DURING INCUBATION AND DRYING

The loss of ammonia by volatilization during incubation and soil drying and contamination of soil samples during drying were studied in the laboratory. Aqua ammonia placement treatments produced a range of soil nitrate and ammonium levels, which produced different amounts of ammonia upon incubation and drying. Recovery of applied N as mineral N and volatilized N in acid traps was virtually complete, indicating that ammonia volatilization was the only significant N loss process. When aqua ammonia was applied to the surface, 57% was volatilized, compared with only 2% when the fertilizer was deep placed. Ammonia volatilization decreased with time; most of the loss occurred during the first day after fertilizer application and ammonia loss was virtually complete within 8 days of incubation. Regression analysis indicated loss of ammonia on soil drying could be explained by the initial ammonia concentration and the time from fertilizer application; approximately 40 days from fertilizer application were required for complete chemical adsorption of ammonia (i.e. no ammonia loss on drying). Unfertilized soils absorbed up to 66 mg N/kg of the ammonia volatilized from fertilized soils when dried together in the same oven. We conclude that where accurate ammonium analysis is required on recently fertilized soil, undried soil should be used. This eliminates ammonia loss during drying and cross-contamination of samples. Drying of soil did not affect the recovery of nitrate N, as nitrate was not volatilized or denitrified.