| Straw is one of the world’s largest numbers of by-products of agricultural production. Straw Resource is huge in our country, in recent years, the production of crop residues is more than 700 million t, but the complete and effective policy mechanisms of comprehensive utilization of straw have not yet formed. The utilization efficiency of crop-straw is still low; the main use is burning directly. Direct burning of straw causes a serious waste of resources, and can easily cause environmental pollution. In addition, during agricultural production applying of fertilizer in great quantity will not only cause the loss of soil fertility, but also cause pollution to groundwater, rivers and lakes, and it is the important source of agricultural non-point source pollution. Crop residues containing large amounts of nutrients like Nitrogen, Phosphorus, Potassium, trace elements, and organic matter, is an inexpensive organic material. Straw is the most direct and effective way of efficiently using of straw resources. Straw can put the most nutrients absorbed by crops into the soil, reduce the use of chemical fertilizer, play an important role of improving soil properties, and is an important way of sustainable development of Agriculture. Therefore, it is particularly important and urgent to carry out the research of optimized fertilization and straw. Through two years of field experiment, this research sets up five experiment processing including the full amount of NPK fertilizer (NPK),90% NPK fertilizer with straw (90%NPK+S),80% NPK fertilizer with straw (80% NPK+S),70% NPK fertilizer with straw (70%NPK+S) and 50% NPK fertilizer with double straw (50%NPK+SS), studying the effect of straw-return with reducing fertilization on soil physical and chemical properties, biological characteristics, soil nutrient status, crop yield and its components, growth traits, quality and so on. The results show that:1. Under the rotation system of rice-vegetable, continuous straw coverage with reducing fertilization have a positive effect on soil properties and nutrient status. With straw treated, soil bulk density decreased by 0.020～0.11g·cm-3, pH value increased by 0.060～0.55, organic increased by 2.55～12.9g·kg-1, total nitrogen content increased by 0.0290～0.941g·kg-1, total phosphorus content increased by 0.033～0.392 g·kg-1, total potassium content increased by -0.200～6.50g·kg-1, available nitrogen content increased by 18.3～65.5 mg·kg-1, available phosphorus content increased by 0.200～13.7 mg·kg-1, available potassium content increased by 4.20～61.5 mg·kg-1.Comparing the full amount of NPK fertilizer, straw-return can significantly reduce the bulk density of topsoil, improve the bulk density, and improve topsoil pH with bringing them closer to neutral. While, continuous straw coverage can also improve topsoil organic matter, total NPK content, available P and K content and is higher than only chemical fertilizer. In summary, the effect of 70%～80% NPK with straw for the full amount on improving soil physical and chemical properties is the most significant.2. Under the rotation system of rice-vegetable, continuous straw coverage with reducing fertilization have a positive effect on soil biological traits. With straw treated, soil invertase activity increased by 11.5%,11.0%,5.8%, protease activity increased by 19.3%,29.3%,23.8%, catalase activity increase by 9.1%,6.4%,0.6%, urease activity increase by 15.6%,45.9%,48.4%, acid phosphatase activity increased by 50.8%,40.3%,6.6%. After the straw returning, the activities of soil converting enzyme, protein powder, catalase, urease and acid phosphatase have significantly improved, higher than NPK fertilizer treatment.In summary, the effect of 70%～80% NPK with straw for the full amount on improving the activities of soil biological traits is the most significant. What’s more, by correlation analysis between soil organic matter, pH, total nutrients and available nutrients with soil enzyme activity, it shows that good soil properties can significantly improve the activities of soil enzyme.3. Under the rotation system of rice-vegetable, the research about effect of continuous straw coverage with reducing fertilization on crop production and economic benefits shows that:straw mulching with reducing fertilizer can increase rice production, the yield increased by 3.03%～17.89%.90% NPK+S and 50%NPK+SS have better results, the yield increased by 17.06% and 16.31%. By correlation analysis with rice production component factors, it shows that panicles and seed setting rate of rice play a major role in rice production (r=0.811**、0.514**), straw can increase rice production by increasing panicle and seed setting rate. And Straw mulching with reducing fertilizer can increase the production of ercai with the yield increased by 12.18%～36.36%, total amino acids, Vitamin C content, reduce the NO3-N content, and has significantly improved for the quality of ercai. Straw mulching with reducing fertilizer can increase the output and output ratio of rice and ercai, effectively improve the economic benefits of rice and ercai,50% NPK fertilizer with double straw is the most affordable fertilizer policy which has the highest output ratio with 21.6、11.6.4. Under the rotation system of rice-vegetable, continuous straw coverage with reducing fertilization have a positive effect on plant quality and NPK uptake. The nitrogen and phosphorus content in different organs of rice expresses as grain> straw, potassium content expresses as straw> grain. By correlation analysis between different treatment and rice nutrient content, it shows that different treatments have significantly positive correlation with potassium and phosphorus content of rice straw and grain and have negative correlation with nitrogen content (r=-0.298、-0.228) showing that straw mulching with reducing fertilizer can increase the phosphorus and potassium content of rice plants, reduce the nitrogen content. Rice production has significantly positive correlation with rice nutrient content, showing that rice nutrient content may have an effect on rice production. By correlation analysis, different treatments have a positive correlation with PK uptake (r=0.629、0.567), a negative correlation with N uptake (r=-0.244), showing that straw mulching with reducing fertilizer can increase the PK uptake of rice plant and reduce the N uptake. What’s more, there are some relationship between NPK content and NPK uptake.To sum up the results,70～80% NPK with full amount of straw (In rice planting season with urea fertilizer applied by 170.8～195.0 kg·hm-2, superphosphate fertilizer applied by 189.2～215.8 kg·hm-2, potassium fertilizer applied by 60.8～69.2 kg·hm-2, straw applied by 7500 kg-hm"2. In ercai planting season with urea fertilizer applied by 383.6～428.4 kg·hm-2, superphosphate fertilizer applied by 266.9～ 305.1 kg·hm-2, potassium fertilizer applied by 136.3～155.7 kg·hm-2, straw applied by 7500 kg·hm-2) is the best way to keep optimal fertilization methods of rice-vegetable rotation patterns. It is an important way to improve soil fertility and increase crop yields under upland cropping conditions. |
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