Effects of combined application of Chinese milk vetch and synergistic materials on nutrient content and microbial community structure in paddy soil

【Objective】 This study aimed to investigate the effects of combined application of Chinese milk vetch （MV） and synergistic materials （SM） on soil nutrient content， microbial communities of paddy soil and their correlations， so as to provide a theoretical basis to achieve high and stable yield through manure-rice rotation model.【Method】 A pot experiment was carried out using rice cultivar Teyou 809 as research subjects. Under two rotation models of winter fallow-rice and Chinese milk vetch-rice， eight treatments were set： winter fallow （CK）， winter fallow+urease inhibitor （CN）， winter fallow+bentonite （CP）， winter fallow+goethite （CZ）， Chinese milk vetch incorporation （MV）， Chinese milk vetch incorporation+urease inhibitor （MN）， Chinese milk vetch incorporation+bentonite （MP）， and Chinese milk vetch incorporation+goethite （MZ）. By integrating soil agrochemical analysis， high-throughput sequencing， and bioinformatics approaches， the effects of different treatments on soil nutrient content and microbial community structure were investigated.【Result】 Compared with CK， the MV treatment significantly increased the total nitrogen content by 4.73% and available phosphorus content by 128.00% in paddy soil （P<0.05， the same below）. Compared with CN treatment， the MN treatment significantly increased the available phosphorus content by 80.03%； but it significantly decreased the total phosphorus by 16.43%， and total potassium by 32.23%. Compared with CP treatment， MP treatment significantly increased the total nitrogen content by 5.26% and total phosphorus content by 13.68% in paddy soil. Compared with CZ treatment， the MZ treatment significantly increased the available phosphorous content by 20.13%， and significantly decreased the available potassium content by 25.04%. No significant difference in soil organic matter content was observed among all treatments （P>0.05）. The application of MV， SM， and their combination could all increase the Alpha diversity of bacterial communities and reduce the richness of fungal communities in paddy soil. The dominant bacterial phyla in paddy soil were Chloroflexi， Proteobacteria， Acidobacteriota， and Bacteroidota； the dominant fungal phyla were unclassified_k__Fungi， Basidiomycota， and Ascomycota. The results of redundancy analysis showed that the contents of total nitrogen， total phosphorus， alkali-hydrolyzable nitrogen， and available phosphorus were the main environmental factors affecting the composition of bacterial communities，and no fungal communities significantly correlated with environmental factors were found. Chloroflexi， Proteobacteria， Acidobacteriota，unclassified_k__Fungi， and Ascomycota were the key groups of soil microorganisms under the applications of MV， SM， and their combinations.【Conclusion】 The applications of MV and the three types of SM are beneficial to improve soil fertility， optimize soil microbial community structure， with the combined application of MV and bentonite showing the best effect and indicating high value for promotion in actual production.