The Effects Of Co-incorporation Of Green Manure And Rice Straw On Dynamic Changes Of Soil Carbon And Nitrogen

Rice straw and green manure are the main organic fertilizer sources in rice fields in southern China.Reasonable utilization can effectively fertilize the soil and reduce the amount of chemical fertilizer.Straw returning can not only solve the environmental pollution caused by incineration,but also promote nutrient recycling.Planting leguminous green manure in winter fallow fields can not only enrich nitrogen nutrients through biological nitrogen fixation,but also release nutrients for crops to absorb and utilize.The C/N ratio of rice straw is large,and it is rich in hemicellulose,lignin and other refractory substances.If a large number of rice straw cannot be decomposed in time after returning to field,it may produce toxic substances,affecting the growth of subsequent crops.Different from rice straw,leguminous green manure is rich in nitrogen nutrients.Combined with rice straw,it can regulate the C/N ratio of biological residues and affect the decomposition of organic materials and nutrient release.Based on the green manure and rice planting areas in the middle and lower reaches of the Yangtze River,this study compared the decomposition rules of different green manure and rice straw,and clarified the nutrient release rate during the decomposition process and the nutrient transformation characteristics of Chinese milk vetch(Astragalus sinicus L.),Vicia villosa and rice straw.The effects of combined application of different types of green manure and rice straw on nutrient release of green manure and straw,and the dynamic changes of soil carbon and nitrogen accumulation were investigated.It provides a theoretical basis for the field management of green manure and rice straw returning mode in the region,and better serves the sustainable development of agriculture.The net bag culture method was used to simulate the green manure and straw returning method to study the decomposition characteristics of rice straw combined with Chinese milk vetch and Vicia villosa and their effects on soil carbon and nitrogen nutrients.The main research results are as follows:1.The decomposition characteristics of rice straw,Chinese milk vetch and Vicia villosa were revealed.Chinese milk vetch(MV),Vicia villosa(VV)and rice straw(RS)were cultured for 180 days to clarify the decomposition law of different organic materials.The results showed that the decomposition of the three organic materials was rapid in 0-10 d,slow in 10-60 d,and stable in 60-180 d.The cumulative decomposition rates of MV,VV and RS were 85.12%,82.58% and 77.22%,respectively,and the average decomposition rates were 0.47 g/d,0.46 g/d and 0.43 g/d,respectively.By comparing the decomposition laws of three organic materials,it can be found that the decomposition rates of MV and VV treatments at 0-10 d were 94.26% and 91.62% higher than those of RS treatment,respectively.10-60 d RS treatment had the fastest decomposition rate,which was 79.43%and 43.14% higher than MV and VV treatments,respectively.The decomposition rates of RS treatment at 90-180 d were 16.36% and 19.20% higher than those of MV and VV treatment,respectively.The overall degradation rate of different organic materials was MV > VV > RS.2.Adding rice straw promoted nutrient release of Chinese milk vetch and Vicia villosa in the middle and late stages of decomposition.Four treatments were set up by comparing the decomposition law of green manure with returning green manure alone and adding rice straw: 1,decomposition of Chinese milk vetch(MV);2.Co-incorporation of Chinese milk vetch and Rice Straw(MV+RS);3 Vicia villosa(VV);4.Co-incorporation of Vicia villosa and Rice Straw(VV+RS).The results showed that the addition of rice straw mainly promoted the decomposition of Chinese milk vetch in 30-60 d.In this period,the decomposition rate,carbon,nitrogen and phosphorus release rate of Chinese milk vetch were significantly increased by 42.68%,32.22% and 19.18%.Adding rice straw mainly promoted the decomposition of Vicia villosa in 60-120 d.During this period,the decomposition rate,carbon,nitrogen and phosphorus release rate of Vicia villosa were significantly increased by 45.40%,41.88% and19.06%.Overall,the addition of rice straw had no significant effect on nitrogen and potassium release of Chinese milk vetch and Vicia villosa.3.The addition of green manure promoted the decomposition and nutrient release of rice straw.In the second part,the effect of green manure on rice straw decomposition was studied.Three treatments were set up: 1.Rice straw decomposition(RS);2.Co-incorporation of Chinese milk vetch and Rice Straw(RS+MV);3.Co-incorporation of Vicia villosa and Rice Straw(RS+VV).The effect of adding green manure on rice straw decomposition was studied.The results showed that adding green manure promoted rice straw decomposition and nutrient release.Compared with the single straw returning,the cumulative decomposition rate of straw was increased by 3.89% and 3.28% respectively at the end of the experiment.The carbon release rate of rice straw increased by 35.48% and30.46% in the early 0-30 d after adding Chinese milk vetch and Vicia villosa,respectively.The nitrogen release rate of rice straw was increased by 7.44% and 13.62%,9.39% and6.82%,2.88% and 0.56% in 0-60 d,60-120 d and 120-180 d,respectively.The addition of Chinese milk vetch and Vicia villosa had significant effects on the phosphorus release rate of rice straw from 0 to 120 d,which increased by 49.89% and 35.84%,respectively.The effect of adding green manure on the release of potassium content was reflected in the early stage of the experiment.The decomposition rate of rice straw was increased by12.68% and 15.96% respectively from 5 to 30 days,and the potassium content in rice straw was basically released after 30 days.4.Straw and green manure could improve soil carbon and nitrogen storage.By setting1,control(CK);2.Rice straw decomposition(RS);3.Chinese milk vetch(MV);4.Vicia villosa(VV);5.Co-incorporation of Chinese milk vetch and Rice Straw(RS+MV);6.Co-incorporation of Vicia villosa and Rice Straw(RS+VV).The results showed that straw and green manure could improve soil carbon and nitrogen storage.After adding organic materials,the contents of soil organic carbon and total nitrogen increased by 0.88%-5.92%and 6.80%-14.56%,respectively.RS+MV treatment had the best effect on increasing organic carbon.RS+VV treatment had the best effect on the increase of total nitrogen.Through the analysis of soil soluble organic carbon in different decomposition periods of organic materials,it was found that the promotion of organic nutrients in the later stage of the experiment was obvious,and the overall effect of MV,VV,RS+VV treatment was better in 120-180 d.They were increased by 18.86 mg/kg,7.05 mg/kg and 7.29 mg/kg,respectively.The effect of green manure on soil ammonium nitrogen increased by 22.12%and 22.75% respectively in VV and RS+VV treatments in the first 5 days.In the middle of the experiment,different treatments fluctuated greatly.At 90 d,organic materials promoted soil ammonium nitrogen significantly,and MV and RS+MV treatments were the most significant,which were 121.88% and 91.84% higher than CK,respectively.120-180 d RS treatment effect is the best,increased by 104.62%.The treatment VV and RS+VV increased soil nitrate by 286.64% and 213.01% respectively,followed by MV and RS +MV by 122.57% and 97.08% respectively.The promotion effect of RS treatment was weak,increasing soil nitrate nitrogen content by 42.21%.