Effects Of Conservation Tillage Of Paddy Fields In Taihu Region

The experiment was carried out in 2006 at the Agriculture Science Institute of Taihu, Jiangsu with three cropping patterns (wheat-rice, ryegrass-rice, rape-rice), two modes of tillage and two modes of crop straw returning to field, hence forming 12 experimental treatments. The main results are as follows.1. Paddy conservation tillage affected dynamic change in main soil fertility factors in growing period of rice. The result showed that the contents of the total nitrogen organic matter and available nitrogen in the soil gently increased in 2005, but were fluctuated at a certain level in 2006. But the available P and K changed sharply and showed no consistent trend between 2005 and 2006.2. The total nitrogen content, organic matter, available N and available K tested at rice harvest were increased in 2006 compared that of 2005, but the available P and soil pH were declined. The total N was increased by 8.95%, organic matter, by 3.85%, available N, by 1.39, and available K by10.38%, but the available P and pH were decreased by 21.33% and 5.71% respectively for the conservation tillage treatment.3. The nitrogen contents in rice plants were higher under straw returning to field but the phosphorous and potassium contents were lower than that of no straw returning in most of the treatments. The conservation tillage could promote nutrient absorption and increase nitrogen, phosphorous and potassium accumulation in late growth stage, hence giving positive influences on rice yield.4. Based on the average yields for wheat-rice, ryegrass-rice, rape-rice cropping patterns in 2005 and 2006, the rice yield were 8751.6 kg/hm2 under conservation tillage, being higher 6.91%, 5.46% and 2.36% than that of no tillage with no straw returning, no straw returning with ploughing and straw returning with ploughing respectively.5. The correlation coefficients between the rice yields and soil available K reached 0.6333, but the rice yield had lower correlation coefficients with pH, organic matter, total N, available N and available P contents of the soil. Furthermore, the correlation coefficients of the rice yields with K contents of rice plants at heading and maturity were 0.7629 and 0.7925, but had lower correlation coefficients with P contents. This showed the enhancement of soil available K under straw returning could be the leading factor of increasing rice yields.