Effect Of Rice Straw Returning In Chinese Milk Vetch-rice System In Southern Anhui Province

Utilization of green manure is traditional and effective method to improve soil fertility and satisfy nutrient supply to the next-stubble crops.It plays important roles in achieving high and stable yield and establishing the friendly environment of agricultural.In the south China,green manure-rice cropping system has peoved to be high-efficiency and sustainability method.In the milk vetch-rice rotation system,the high-yield cultivation of milk vetch and the combined utilization of milk vetch and rice straw were important measures for the development of green manure production and efficient utilization of rice straw resources.In this research,the effects of different amounts of rice straw and nitrogen（N）fertilizer on fresh biomass of milk vetch and soil properties were studied by pot experiments;the yield and nutrient absorption characteristics of rice at different growth stages were studied by dynamic sampling based on field experiment,and the effects of soil fertility and chemical fertilizer substitution under the combined utilization of rice straw and milk vetch were evaluated,and its mechanisms were furthur investigated.The main results are as follows:（1）Rice straw returning combined with N fertilizer can improve soil fertility and achieve high fresh biomass of milk vetch.Rice straw addition and N fertilizer application significantly increased the fresh biomass and shoot N,phosphorus（P）and potassium（K）accumulation of milk vetch.Compared with rice straw treatment,N fertilizer treatment had a stronger positive effect on fresh grass yield and nutrient accumulation of milk vetch,and the combined application of thees two factors had a more significant fresh biomass increase effect.The total amount of rice straw returned to the field combined with 45-90kg/hm² N fertilizer was more conducive to the increase of fresh grass yield（fresh biomass increase rate was 57.5%～171.2%）and nutrient absorption（accumulation of N,P and K increased by 70.5%～141.1%,45.3%～80.8%and 102.9%～151.6%respectively compared with the control）.Application of straw and N fertilizer significantly increased soil enzyme activities.The activity of soil L-leucine aminopeptidase increased at first and then decreased with the increased amount of straw at all the four N levels.The other five soil enzyme activities were strongest at RS2 treatments when N levels were N0,N45 and N135,while that in RS1 treatment was strongest at N90 level.Results of aggregated boosted trees analysis showed that soil readily available K content and N-acetyl-glucosaminidase activity were the most important indicators,and respectively contributed 52.6%and 30.0%to the fresh biomass of milk vetch.（2）The combined utilization of milk vetch and rice straw increased rice yields,and promoted nutrient absorption and N use efficiency of rice.Under the condition of reducing 40%N fertilizer,the rice yield could be maintained by utilization of milk vetch(MN₆₀)and combined utilization of milk vetch and rice straw(MSN₆₀),and the contribution of planting milk vetch to rice yield was greater than that of returning rice straw to the field.Rice growth stage and fertilization treatment had significant effects on shoot N,P and K accumulation,and the interaction between them had significant effect on N accumulation.The accumulation of N,P and K in the shoot of rice was no significant difference among the treatments at tillering stage,and the change trend was similar at booting stage and maturity stage.Compared with N₆₀,MSN₆₀ increased the N accumulation of rice shoot by 84.45%and 26.76%at booting stage and maturity stage,and there was no significant difference between MSN₆₀ and N₁₀₀;the P and K accumulation of MSN₆₀ was the highest,compared with other N treatments,P accumulation at booting stage and maturity stage increased by4.87%～29.92%and 6.21%～28.84%respectively,potassium accumulation increased by7.74%～37.50%and 6.06%～22.85%respectively.At the same time,the combined use of milk vetch and rice straw can effectively improve the rice N contribution rate,N use efficiency,N agronomic efficiency and N partial productivity.（3）The combination of milk vetch and rice straw can effectively improve the soil fertility of paddy soil.The change trend of soil inorganic N and available P content was similar to that of shoot N and P accumulation during rice growth period.The results showed that the application of milk vetch and combined usage of milk vetch and rice straw could effectively improve soil fertility,and the joint utilization could improve soil fertility more comprehensively.The content of soil inorganic N in MSN₆₀ treatment was the highest before transplanting and at maturity,with the increase of17.54%～69.05%and 1.78%～19.46%compared with other N treatments respectively.At the maturity stage of rice,MSN₆₀ treatment had the highest contents of total nitrogen and organic matter.Compared with N₆₀ and SN₆₀ treatment,total nitrogen increased by 7.51%and 9.59%,and organic matter increased by 13.62%and 2.61%,respectively.In addition,the combined utilization of milk vetch and rice straw could significantly increase the activities of soil enzymes related to carbon transformation and acid phosphatase,and reduce the activities of urease.（4）Soil total N content and urease activity were the dominant factors of rice yield and shoot N accumulation during rice maturity,the contribution rates to rice yield were 27.45%and 30.03%respectively,and the contribution rates to aboveground nitrogen accumulation were 24.15%and46.95%respectively.Application of milk vetch had a significant positive effect on soil total N,available nutrients and enzyme activities,and had a strong positive effect on rice yield and shoot nutrient accumulation at rice maturity.The results of soil fertility indexes of milk vetch utilization and co-utilizaiton of milk vetch and rice straw treatments were similar,and the results of rice yield and plant nutrient accumulation of co-utilizaiton of milk vetch and rice straw treatment and conventional nitrogen application treatment were similar.In conclusion,rice straw returning combined with N fertilizer and co-utilizaiton of milk vetch and rice straw can effectively solve the problem of rice straw resource utilization.Co-utilizaiton of milk vetch and rice straw can improve soil fertility,promote rice nutrient absorption,and achieve stable rice yield under the condition of reducing chemical fertilizer,which is an important measure to realize the green and sustainable development of rice field.