Effects Of Green Manure Combined With Nitrogen Fertilizer On Soil Microbial Community And Rice Yield In Karst Paddy Field

Karst soils in southern China are subject to obvious environmental constraints,and the environmental problems caused by unreasonable fertilization have been intensified in recent years.As a natural organic fertilizer source,green manure is widely used in rice crop rotation system,which has a positive effect on maintaining soil ecological functions.However,relatively few studies have been conducted on the effects of green manure crop rotation on rice production in southern karst rice areas,and there is still a lack of comprehensive analysis on the response of soil physicochemical properties and microbial community characteristics to rice yield characteristics under the conditions of green manure with N fertilization.Therefore,in this study,we monitored the association between rice production and soil microbiology under the conditions of green manure,N fertilizer and their combined application,and explored the contribution of soil physicochemical properties and soil microbial community to rice growth characteristics and yield under the treatment of green manure with N fertilizer,relying on field location experiments and using high-throughput sequencing and other techniques.The main findings were as follows.（1）Green manure return to the field was beneficial in maintaining soil nutrients.Compared with no N fertilizer application,SOM content increased by 2.93%to 10.17%,TN increased by 6.34%to 7.81%,AN increased by 9.78%to 11.27%,NH₄⁺-N increased by111.47%to 202.29%and NO₃^--N increased by 131.38%to 191.49%in green manure with60%,80%and 100%N fertilizer treatments.（2）Green manure with N fertilizer affected soil microbial community structure and species distribution.Green manure with 60%,80%and 100%N fertilization increased the abundance and diversity of bacteria but decreased the abundance and diversity of fungi compared to no N fertilization.Bacterial-fungal co-occurrence network structure was mainly composed of six modules,where module 2 and module 3 occupied the core of the co-occurrence network and were dominated by fungal and bacterial interactions of species within the modules,respectively.In addition,soil microorganisms showed close correlation with physicochemical properties under green manure with N fertilization.SOM,NH₄⁺-N,NO₃^--N and AK significantly affected the distribution of bacterial communities,while AN,NH₄⁺-N,NO₃^--N and AK significantly affected the distribution of fungal communities.（3）Photosynthetic characteristics of rice and rice yield traits were significantly better in the green manure with N fertilizer treatment than in the no fertilizer treatment.Compared with no N fertilizer,the SPAD value,P_nand G_sof rice leaves were significantly increased by4.53%～7.29%,14.31%～16.43%and 6.02%～15.45%,respectively,in the green manure with60%,80%and 100%N fertilizer treatments;meanwhile,the effective spike,spike length and spike grain number of rice were also significantly increased by The effective spike length,spike length and spike grain number of rice also increased significantly by 14.07%～17.75%,6.33%～7.50%and 10.29%～12.48%.Compared with no fertilizer application,rice yield was significantly increased by 34.99%,36.36%and 41.85%in green manure with 60%,80%and100%N fertilizer treatments.In addition,soil N and SOM content in all forms significantly affected rice yield,which was both directly affected by soil physicochemical and indirectly affected by fertilizer application treatments.In conclusion,green manure with 80%N fertilizer is recommended as the optimal fertilization measure for rice production in karst areas in the rice cropping system.