Impacts Of Soil Tillage Methods And Crop Straw Recycling On The Soil Fertility Of Rice Field In The Region Along Yangtze River Of Jiangsu Province

Soil tillage and crop straw recycling are two important cropping practices in rice cultivation. In this paper, we conducted a field experiment to investigate the impacts of different tillage methods and crop straw recycling on the soil fertility in typical rice-wheat rotation paddy field in the region along Yangtze River of Jiangsu Province. Three tillage methods (conventional plough tillage, rotary tillage and no-tillage) and one straw returning method were selected in this experiment. We investigated the effects of tillage methods and crop straw returning on the contents of soil organic matter, soil available nitrogen, and soil available Phosphorus, and analyzed the affecting force of tillage methods and crop straw recycling on the soil fertility. The main results are showed below:(1) The impacts of soil tillage and crop straw returning were different on three layer soils at different periods of rice growing season. Crop straw significantly increased the contents of organic matter in0-7cm soil layer from seeding stage to filling stage, only significantly raised the contents of organic matter for1.5-5%in7-14cm and14-20cm soil layers from tillering stage to booting stage. The contents of organic matter in0-7cm soil layer were higher in rice field under plough tillage or rotary tillage than no-tillage during the early period of rice growing season(from seeding stage to jointing stage), while it was opposite in7-14cm and14-20cm soil layers during the late period of of rice growing season (from booting stage to harvested). After rice harvested, the soil organic matter contents in0-7cm soil layer of plough tillage+crop straw returning, rotary tillage+crop straw returning, no-tillage, and no-tillage+crop straw returning treatments were significantly raised by5.7-11.2%as compared to plough tillage treatment. While the soil organic matter contents in7-14cm and14-20cm soil layers were showed no significant difference among different treatments. The results of affecting force showed that the crop straw and soil tillage presented relative higher affecting force at late period of rice growing season than later period. Crop straw had similar affecting force on three soil layers. Soil tillage presented higher affecting force on0-7cm soil layer than7-14cm and14-20cm soil layers. The affecting force of their interaction was lower than that of sole one.(2) The impacts of crop straw returning and soil tillage were different. Crop straw significantly raised the contents of soil ammonium nitrogen at filling stage and mature stage. While its impact on the contents of soil nitrate nitrogen was more complex. Crop straw returning significantly reduced the soil nitrate nitrogen contents at seeding stage, but significantly increased the soil nitrate nitrogen contents from booting stage to manure stage, and had not significant effect on the contents of soil nitrate nitrogen at tillering stage and jointing stage. The impacts of soil tillage on the contents of soil nitrate and ammonium nitrogen were different at different stages and layers. There was not significant difference in the impacts of three tillage methods on the contents of soil nitrate and ammonium nitrogen at seeding and tillering stages. From jointing stage to mature stage, the contents of soil nitrate and ammonium nitrogen in no-crop straw returning rice field generally showed a similar trend:no-tillage> rotary tillage or plough tillage; in the crop straw returning rice field, the nitrate and ammonium nitrogen contents in0-7cm soil layer showed a same trend: no-tillage> rotary tillage or plough tillage; but the nitrate and ammonium nitrogen contents of7-14cm and14-20cm soil layers showed a opposite trend. Crop straw returning and soil tillage had significant impacts on the accumulation of soil ammonium nitrogen in0-7cm and14-20cm soil layers. Crop straw returning had significant impact on the accumulation of soil nitrate nitrogen in all three layers, while soil tillage had not significant impact. The results of affecting force showed that soil tillage, crop straw and their interaction effect presented significant affecting force on the soil ammonium nitrogen after jointing stage. Soil tillage showed higher affecting force on0-7cm soil layer than7-14cm and14-20cm soil layers. While the affecting force of crop straw was opposite. Soil tillage and crop straw mainly showed significant affecting force on the soil nitrate nitrogen at the early and late period of rice growing season. Their affecting force on soil nitrate nitrogen was higher on0-7cm soil layer than7-14cm and14-20cm soil layer.(3) Crop straw returning was also mainly affected the contents of soil available phosphorus during late period of rice growing season, and its impact were similar on three soil layers. Crop straw returning significantly increased the soil available phosphorus contents from booting stage to manure stage. The impacts of soil tillage on the contents of soil available phosphorus contents were different at different stages and layers. The contents of available phosphorus in0-7cm soil layer were higher in rice field under plough or rotary tillage than no-tillage during the early periods of rice growing season; while the contents of available phosphorus in0-7cm soil layer were lower in plough or rotary tillage rice field than no-tillage rice field during the late periods of rice growing season. The contents of available phosphorus in14-20cm soil layer were higher in plough tillage rice field than rotary or no-tillage rice field during all stages of rice growing season. The results of affecting force showed crop straw had significant affecting force on all three soil layers after jointing stage. Its affecting force was higher on7-14cm and14-20cm soil layers than0-7cm soil layer. The affecting force of interaction effect showed similar trend. The affecting force of soil tillage was higher on0-7cm soil layer than7-14cm and14-20cm soil layers.