Effects of interaction of different factors on nitrate nitrogen accumulation and pH of brown soil

A constant temperature incubation experiment was conducted to evaluate effects of temperature (10℃ and 30℃), soil moisture content (70% and 100%), ureanitrogen rate (0, 450, 600 and 750 mg/kg) and their interaction on nitratenitrogen accumulation and soil acidification. The results show that nitrification is slowly under 10℃, and significantly negative and positive correlations are found between Kmax (maximal nitrification rate) and ureanitrogen rate (r=-0.935**), t0 (time of maximal nitrification rate) and ureanitrogen rate (r=0.876**), respectively. The nitrification rate is increased as the increase of the ureanitrogen rate under 30℃. Days of t0 are prolonged under the low temperature. The t0 values of the ureanitrogen rate of 750 mg/kg under 10℃ are 1.9 and 2.5 times larger than those under 30℃ with soil moisture of 70% and 100%, respectively. An exponent increasing trend is found between the nitrate nitrogen accumulation and the degree days after urea application in all treatments, and the accumulation amount is higher with soil moisture content of 70% than that of 100%. Significant accumulations are found under the ureanitrogen rates of 600 and 750 mg/kg. Soil pH values of all treatments are lower than that of the initial soil under 30℃, and pH values of ureanitrogen rates of 600 and 750 mg/kg are less than 5.1, which shows a significant acidification. Results of the path analysis show that amount of ureanitrogen and incubation day are two key factors that affected nitrification rate and then affected soil pH, and the other factors are incubation temperature and soil moisture content.