| The decomposition characteristics of rice straw, wheat straw, rape straw, the change of soil nutrients, different available carbons and carbon pool management index were discussed under straw mulching on two kinds of different parent materials soil in Chengdu plain and Central Hilly Area of Sichuan. It shows that:The accumulative total decomperation ratio of wheat straw,rape straw was as high as 50% in the early stage,and then pulled down in the late.But the decomposition characteristics of rice straw was contrary to wheat straw,rape straw.after one years time, and the decomperation ratio of three kinds straw fell into the same class.During same time, the accumulative total decomperation ratio and decomperation rate was bigger in Chengdu plain than that of Central Hilly Area. The humification coefficient of rice straw, wheat straw and rape straw was change from 0.22 to 0.32 in two trial places. Jenny model was carried out to forecast soil carbon balance: 15.61 ton of rice straw was needed to raise soil carbon from 12.86g/ kg to 20g/ kg independently,and 14.64 ton of wheat straw as wellStraw is rich in nutrient, the content of nitrogen is 0.77%～1.24%, and phosphor is 0.09%～0.23%, and potassium is 1.14%～2.25%. Straw returned to soil can increase the content of nitrogen, phosphor and potassium. The effect of straw returned to soil on soil fertility was investigated through a fixed field experiment. The results indicated that Straw-mulching treatment increased the content of toal nitrogen, available nitrogen, total potassium and available potassium, especially the available potassium improved 73% in Chengdu plain comparing with CK. There's no evident rule about the change of soil phosphor between different treatments.When strawed retune to soil,the available nitrogen and available phosphor of no-tillage treatment was lower than that of plow-tillage treatment,but plow-tillage treatment turned over the soil that increased the movement of hydronium of potassium,so the total potassium and available available was lower than that of no-tillage treatment,but there's no exceedingly significant difference between two treatments.Soil organic carbon is one of an important index to appraise soil fertility.It can improve soil organic carbon when straw returned to soil according to a three years, fixed field experiment,and the content of organic carbon HF＞HM＞CK,the treatments of HM and HF increased 2.64%,18.66 % respectively comparing with CK in trial place: of Chengdu plain,and the trial place of Central Hilly Area of Sichuan increased 8.01% and 20.37 % as well. The annual increasing ratio of soil organic carbon of the theatment HM reached 0.017%～0.034 %,but the theatment HF was bigger than that of HM because of too much of undecomposited straw remained in soil, and it reached 0.087%～0.118 %.The Stable-oxide coefficient of soil organic carbon reduced when straw returned to soil comparing with CK, and the treatments of HM and HF reduced 30.22%,34.72% respectively in trial place of Chengdu plain, and Central Hilly Area of Sichuan reduced 40.57%,53.14%. Strawreturnedto soil can improve the content of CA,CMB,CM by 42.30～50.56 %,13.22～164.35 %, 15.67-159.45 % respectively, and CPMI increase 9.25 %～38.51% in Chengdu plain,and 48.20%～54.42% as well in Central Hilly Area of Sichuan.Treatment of HF can improve the quality of available carbon comparing with treatment of HM.The results of correlation analysis demonstrated that CPMI can reflect the dramatic variation of soil fertility and soil carbon more actively than that of soil organic matter. |
