Dynamic Changes Of Rice Growth And Soil Nutrients In Jianghan Plain Under The Condition Of The Return Of Chinese Milk Vetch And Straw

Planting Chinese milk vetch(CMV)and returning rice straw are the important conservation tillage techniques in the paddy field.There were plenty of reports on single application of CMV or rice straw and its effect.With the implementation of the policy of banning straw burning in China,the green manure cultivation under returning rice straw is becoming common,but the research on their combining effects is relatively less.The C/N ratio of the combination of green manure with straw was more appropriate for microbiology growth than single,which might effectively improve soil fertility,reduce chemical fertilizer and promote green rice production.A two-year field trial,including 3experiments(CMV,rice straw and their combination under different nitrogen(N)fertilizer rates;different amounts of N fertilizer under the combination of CMV and rice straw;CMV and rice straw combined with chemical fertilizer under the condition of the same total nutrient input),was conducted to determine the effects of CMV,straw and their combination in Jianghan plain,Hubei Province.The dynamics of rice growth,rice nutrient accumulation,and soil nutrient content were measured.This study aims to reveal the differences between the application of CMV and rice straw and the chemical fertilizer application in nutrient supply and rice nutrient uptake,and furthermore,provide technical and theoretical basis for the optimized application of CMV and rice straw returning in rice production.The main results are as follows:(1)Under different N levels,the yields of rice grain and rice straw were increased by the combination of CMV and rice straw and the single application of CMV,but the increasing effect of rice straw returning alone was not significant.The results of logistic growth curve fitting showed that the maximum growth rate of rice under different N levels of CMV combined with rice straw returning was higher than that of single application of CMV,rice straw,or chemical fertilizer.The increased rates were12.1%-18.1%,31.8%-94.9% and 5.9%-35.0% under the three N application rates.(2)At the same N application rate,CMV,rice straw and their combination increased soil organic matter and total N content at different growth stages of rice.The effect of CMV and its combination with rice straw was more obvious in most cases,thus increasing rice N content,N accumulation,maximum N accumulation rate,and apparent N use efficiency.(3)When the fertilizer application rate was reduced or increased by 50% under the combination of rice straw and CMV,the contents of soil organic matter,total N,available phosphorus and available potassium in different growth stages of rice were generally higher than those of single application of chemical fertilizer,and the accumulation of N,phosphorus and potassium of rice were also close to or higher than those of single fertilizer application.Rice straw combined with CMV could alleviate the effects of excessive or insufficient fertilizer application on rice growth and rice yield by regulating soil N supply and rice nutrient uptake.(4)Less than 50% of the total N input was replaced by the single application or the combination of CMV and rice straw resulted in the equivalent effect with the whole chemical fertilizer application.There were no significant differences in the N,phosphorus and potassium accumulation by rice at different growth stages,and the dry biomass and maximum accumulation rate were close to each other during the growth process,thus no significant differences in the yields of rice grain and rice straw.