Effects of soil amendment on nitrogen mineralization of soils at two altitudes in northwest Guizhou

To evaluate the effects of soil amendment on nitrogen mineralization characteristics of soils at different altitudes, a simulated field experiment was conducted to study the effects of soil amendment on nitrogen mineralization and nitrification in soils, yellow soils (Q) at the altitude of 1 320 m and brown soils (W) at the altitude of 2 120 m from Bijie in Guizhou. Stanford method (aerobic culture method under indoor constant temperature and intermittent leaching) was adopted, and the control and three treatments with different T20 addition rates (1%, 2% and 5%) were set up. The results showed that comparing with the control, the accumulated mineralized N of Q1(Q+1%T20), Q2(Q+2%T20), Q3 (Q+5%T20), W1(W+1%T20) and W2(W+2%T20) increased by 21.35%, 37.66%, 26.06%, 10.83% and 5.71%, respectively; however that of W3 (W+5% T20) decreased by 4.50%. With the rise of T20 addition rate, the accumulated mineralized N decreased. The fitting results of quasi-one stage kinetic equation N_t=N_t0 (1-e^-kt)indicated that there was a good correlation between the amount of accumulated mineralized N and time. Determination coefficient R² (0.956 3-0.985 9) from the fitted equation had significantly difference. Mineralization potential (N₀) of yellow soil was 69.45 mg·kg^-1 on average. Soil mineralization rates (k) of the treatments with different addition rates were higher than the control, and soil mineralization rate increased with the rise of addition rate. Accumulated mineralized N (N_t, N₁₅/N_t and N₀/TN) and mineralization index (N₀×k) of different treatments increased first then decreased, and mineralization potential (N₀), accumulated mineralized N (N_t, N₁₅/N_t and N₀/TN) and mineralization index (N₀×k) of brown soil decreased with the increase of T20 addition rate. The fitting results of equation N_tNO3=N_t0/(1+e^a-bt) showed that the determination coefficient R² (0.983 2-0.999 9) from the fitted equation for nitrate N accumulation in soils at two altitudes and time significantly differed. With the increase of T20 addition rate, V_max and T_max increased first then decreased, nitrification promotion rates of Q increased from -8.34% to 7.90%, mineralization promotion rates of Q and nitrification promotion rates of W increased first then decreased, and mineralization promotion rate of W decreased from 10.80% to -4.49%. Therefore, application of 2% soil amendment promoted the mineralization and nitrification of soil organic nitrogen in tobacco-planting areas of northwest Guizhou, which is beneficial to improving the effective use of N and promoting the soil fertility at the two altitudes in northwest Guizhou.