| Incorporation leguminous green manure to the field can provide nitrogen for subsequent crops,and retain and activate some nutrients,which can effectively improve the nutrient utilization efficiency of crops and increase yield.To study the effects of incorporation green manure on the nitrogen and phosphorus nutrient utilization efficiency and microorganisms of rice and explore the key influencing factors of green manures on crop nutrient utilization efficiency,and provide theoretical basis for the return of green manure to the rice field ecosystem in the karst region of Guizhou,this study planted and applied of green manures to paddy fields in the winter fallow fields in karst areas of Guizhou province,with no chemical fertilizer(CK)applied,local traditional fertilization(CF),and alfalfa(AL),milk vetch(ML),and ryegrass(RY)green manures in combination with 80%chemical fertilizer,respectively,were used in our study.The main research findings are as follows:(1)Compared with CF,grain yield,straw and root of rice biomass in AL treatment were increased by 16.91%,21.92%,and 35.73%,respectively;,grain yield,straw and root of rice biomass in ML treatment were increased by 10.22%,12.77%,and 23.69%in 2021,respectively.In 2022,rice grain yield,straw biomass,and root biomass were decreased by 9.05%,5.95%,and 22.65%,respectively;Grain yield and straw biomass in RY treatment were increased by 3.69%and 15.16%,respectively,while the root biomass was increased by 52.07%in 2021 and decreased by 8.90%in 2022.The biomass of rice roots and straw,the number of grains per panicle,effective tillering,and chlorophyll content showed significantly positive correlation with rice grain yield.The positive effect of green manures on rice production was higher in the first year than that in the second year.(2)Incorporation green manure to the field increased the nitrogen and phosphorus content and absorption of rice roots,stems,and grains,with the nitrogen and phosphorus absorption of grain>straw>root.Application of green manures improved the agronomic efficiency,absorption rate,and utilization rate of nitrogen and phosphorus fertilizers in rice,with AL being the highest.The agronomic efficiency,absorption rate,and utilization rate of nitrogen fertilizer in AL treatment were increased by 64.85%,287.96%,and 161.90%on average,repectively,over the two years compared to CF treatment;The agricultural efficiency,absorption rate,and utilization rate of phosphorus fertilizer were increased by 64.85%,130.59%,and 102.16%on average,repectively.The agronomic efficiency,absorption rate,and utilization rate of nitrogen fertilizer in ML and RY treatments were increased by 29.96%,33.83%,97.62%,and 104.64%,61.60%,and 68.08%,respectively;The agricultural efficiency,absorption rate,and utilization rate of phosphorus fertilizer were increased by 29.96%and 33.83%,45.35%and 58.17%,42.01%and 51.21%,respectively.(3)Application green manure has a trend of increasing soil total nitrogen,available nitrogen,microbial biomass nitrogen,and urease activity.Compared with CF,AL,ML,and RY treatments increased soil nitrate nitrogen by an average of 14.41%,13.00%,and 6.82%over the two years,while soil ammonium nitrogen were increased by an average of 43.87%,23.78%,and 18.89%,respectively,over the past two years.Green manure treatments significantly increased the microbial biomass nitrogen content.Structural Equation Modeling(SEM)analysis showed that green manures indirectly improved nitrogen fertilizer utilization efficiency by promoting soil available nitrogen content,rice grain yield and biomass,as well as straw and grain nitrogen content.Chemical fertilizer had a significant direct negative effect on rice nitrogen fertilizer utilization efficiency.Compared with CK,application green manure treatments reduced the Chao index of nitrogen functional genes and increased the Shannon index.Compared with CF,AL treatment could increase the relative abundance of ureC,nifD and nifH genes related to soil nitrogen cycle,and there was significantly negative correlation between the relative abundance of nifH gene and soil N:P.(4)Green manures can increase the content of total phosphorus and available phosphorus in the soil.Compared with CK,application of green manures increased the content of NaHCO3-P.Compared with CF,soil acid phosphatase activity was increased in green manure treatment.SEM analysis shows that green manure indirectly improved phosphorus fertilizer utilization efficiency by promoting biomass and phosphorus content in grains and straw,while chemical fertilizers had a significant direct negative effect on phosphorus fertilizer utilization efficiency in rice.CK,CF,AL,ML and RY screened 19,21,23,19 and 14 phosphate solubilizing strains respectively,and identified 3,6,8,5 and 5 different genera of strains,with Pseudomonas as the main,accounting for 54.17%,followed by Bacillus,Ensifer,etc.The phosphorus dissolving index(PSI)of each phosphorus dissolving strain was 2.28～4.20,and the phosphorus dissolving amount was 54.35-777.32 mg/L.The AL21 strain isolated in AL treatment had the highest phosphorus dissolving amount,which was identified as Pseudomonas by phylogenetic tree.In summary,planting leguminous green manure in winter fallow fields,especially alfalfa green manure,can effectively improve soil nutrients and soil enzyme activity in rice,thereby improving the absorption and utilization efficiency of nitrogen and phosphorus nutrients in rice.By reducing the amount of chemical fertilizer by 20%,rice yield can be increased. |
