Effect of the quantity and duration of application of simulated acid precipitation on nitrogen mineralization and nitrification in a forest soil

Abstract

A study was conducted of the influence of the rate of application of simulated acid rain on N mineralization and nitrification in a forest soil. The rates were varied by applying different quantities of simulated rain for varying periods of time. The soil was exposed in the laboratory to simulated rain at pH 3.5, 4.1, or 5.6 at rates equivalent to 1.5, 2.3, 4.6, 7.1 or 15 times the average rate of precipitation in the field, and then mineralization of soil N or oxidation of added ammonium was determined. The rates of N mineralization were inhibited by precipitation at pH 3.5 or 4.1 when applied for 27 to 234 day at rates 1.5 times greater than that which occurs in nature. Nitrogen mineralization was not affected by simulated rain at pH 3.5 or 4.1 in soils exposed for 156 day at 2.3 times the natural rate of precipitation, for 27 or 81 day at 4.6 times the natural rate, for 54 day at 7.1 times the natural rate, or for 234 day at 15 times the natural rate. On the other hand, mineralization was fastest in soil exposed to pH 3.5 rain for 234 day at 4.6 times the natural rate of precipitation and for 81 day at 15 times the natural rate. Nitrate formation in soil amended with ammonium was inhibited by rain of pH 3.5 regardless of the intensity of rain or the duration of exposure. For a constant rate of rain application, the inhibition of nitrate formation in ammonium-amended soil generally increased with longer periods exposure. The data show that the use of different rates of additions of artificial rain or different periods of exposure to the simulated precipitation will lead to different conclusions on the influence of acid rain on N mineralization in soil.