| Crop straw as the most important byproduct in agricultural production is one of many useful and renewable material resources. China an agricultural country produces about 800 million t amount of crop straw every year, which accounts for 30% in the world. With the development of conservation tillage, straw return acts as an effective utilization way, not only can solve the problem of environmental pollution from traditional straw burning, but also plays an important role in improving soil fertility, and promoting agricultural sustainable development. This research started from June 2011 to June 2013 and the experimental site is located at Xiaohu Country, Huaisi Town Yangzhou City, Jiangsu Province. By conducting field plot test, we studied short-term effects of different amounts of straw return on soil nutrients, soil enzyme activity, soil carbon pool and rice and wheat yield in rice-wheat rotation fields. The aim was to explore a suitable amount of straw return for local production, and provide theoretical and practical basis for improving soil fertility and perfect the local straw counters-field technology. The main conclusion in this research as follows:1. Suitable amount of straw return had significant effect on improving soil nutrients and crop yieldWhether in rice season or in wheat season, straw return could significant increase soil total nitrogen, available phosphorus and available potassium contents, and also increased the rice and wheat yield. The soil nutrients and crop yield ranked in the order:both rice and wheat straw return> only one season straw return> on straw return. In rice season, the treatment of consecutive 4500 kg·hm-2 amount of wheat straw return+6750 kg·hm-2 amount of rice straw return had the most significant effect on soil total nitrogen and available potassium contents. While in wheat season, the treatment of consecutive 3000 kg·hm-2 amount of wheat straw return+4500 kg·hm-2 amount of rice straw return had the most significant effect. In crop yield, the treatment of consecutive 3000 kg·hm-2 amount of wheat straw return+4500 kg·hm-2 amount of rice straw return had highest rice yield and wheat yield, and which increased 20.7% than that of no straw return. Therefore, suitable amount of straw return could improve the soil nutrients and increased the crop yield.2. Suitable amount of straw return had obvious effects on soil enzyme activity and microbial biomass carbon and nitrogen contents.Straw return could improve soil sucrase, catalase and urease activity. In rice season, the treatment of consecutive 3000 kg·hm-2 amount of wheat straw return+4500 kg·hm-2 amount of rice straw return had the most significant effect on soil sucrase and catalase activity. While in wheat season, the treatment of consecutive 4500 kg·hm-2 amount of wheat straw return+6750 kg·hm-2 amount of rice straw return had obvious effect. For urease activity, the full amount of both rice and wheat straw return had the significant effect in both rice season and wheat season. Straw return could increase the soil microbial biomass carbon and nitrogen contents in different soil depths, showing as:both rice and wheat straw return> only one season straw return>no straw return, and among them, more than half the amount of straw return had more apparent effects. Therefore, suitable amount of straw return could improve microorganism quantity and activity and improve the soil environment.3. Suitable amount of straw return could improve soil organic carbon contentNo matter in rice season or wheat season, straw return could increase the soil total organic carbon and labile organic carbon contents in the three soil depths (0～7,7～14 and 14～21cm), and performed as:both rice and wheat straw return> only one season straw return> no straw return. With the increase in soil depth for all treatments, soil total organic carbon and labile organic carbon contents generally decreased, indicting that straw return could affected the vertical distribution of soil organic carbon. The influence of straw return on soil organic carbon in different soil depth was different, but with the same regularity: consecutive middle and higher amount of straw return> consecutive low amount of straw return. For the third rice season, at 0～21cm soil depth, the treatment of consecutive 4500 kg·hm-2 amount of wheat straw return+6750 kg·hm-2 amount of rice straw return had the significant higher soil total organic carbon, easily oxidizable carbon and water-souble organic carbon than that of no straw return. In wheat season, at 0-21cm soil depth, soil total organic carbon and easily oxidizable carbon contents in the treatment of consecutive 3000 kg·hm-2 amount of wheat straw return+4500 kg·hm-2 amount of rice straw return were the highest. In a word, within the scope of this amount, straw return could increase soil total organic carbon and labile organic carbon contents, and the treatments of middle and high amount of straw return had the obvious advantages than others. Therefore, appropriate amount of straw returned could play an important role in increasing soil organic carbon sequestration. |
