Ph Changes In Soil N2o Emissions

I~H ?~i~ ?38 ? Abstract N20 plays an unnegligible role on the greenhouse effect and the destruction of the ozone layer. The N20 emission from agricultural productivity ,mainly producted by soils accounts for the major part of anthropogenic N20 emissions, The physical and chemical characteristies of soil may effect the microbial constitution and enzyme activities, therefore effect the N20 emission rates. So the effect of soil pH on the N20 emission rates were assessed. The experiments were carried out in the laboratory. Three soils were sampled: an acidic soil(pH 4.4), a neutral soil(pH 6.5) and an alkaline soil(pH 7.75). The acidic soil was taken from Red Earth Experimental Station of Chinese Academy of Science in JiangXi province, and the neutral and the alkaline soils were taken from the agricultural soil in Germany. The experiments on the acidic soil were conducted in Yangzhou University, and the experiments on the neutral and alkaline soils were conducted in the University of Giessien in Germany. By adding acidic or alkaline, three soils were adjusted to four different pH values respectively. The acidic soils were amended with either NH4~ and incubated aerobically to investigate the effect of pH on the N20 emission in nitrification, or appliced NO; and incubated under anaerobic conditions, to investigate the effect of soil pH on the N20 emission in the process of nitrate reduction. In the NH4~ treatment, after each gas sampling the incubation bottles of all other treatments were filled with fresh air to maintain aerobic condition, the N~O emission rates were calculated (ug N20-N Kg ). For the neutral and the alkaline soils, the experiments which soil pH effects the N20 emission in the reduction of N0 were conducted. Soil samples ~vere added with either KNO3 or KNO3-i-Glucose, then filled with N2 to anaerobic incubation for 24h, then filled new N2, gas samples were withdrawed after 0 mm, 45 mm, then the concentration of N in the soils were analysised. The total nitrogen losses (N20+N2) in the reduction of NO1 were measured by C2H2 methods ,and the N20 emission rates were presented (rng N20-N Kg1 W?. From our investigat ions, we can conclude as following: ~k 4J~: pH (4 盝i.~ N20 ~t i~f~fYj(iJf~- 39 During the oxidation of NH4~. only small N20 emission were observed, which accounted for about 0.020/0 of applied NH4~ -N, and the N20 emission showed no significant differences between various soil pH levels during the entire incubation period. Under aerobic conditions, the conversion of NH to NO and NOY was improved with increasing pH, and the N20 emission decreased. ? The nitrate reductase activity became high with increasing pH, and the reduction of N0 to N07 was improved. However, due to restricted C availability, the conversion of NO7 to N20 was inhibited, leading to nitrite accumulation and only minor changes in N20 emission. ? The optimum pH for N20 emission were varied in different soils. For the acidic soil, the highest N20 emission rates was observed at pH 6.7, the alkaline soil was at pH 5.9, the neutral soil was at p1-I 5.25. The lowest N20 emission rates were observed at pH 4.4. 7.7 and 7.44 for the acidic soil,...