Abstract:Reclaiming new arable land through engineering measures is an important way to increase cultivated land area in China. However, the main problem of these new arable lands is the low content of soil organic matter, and the cultivation of farmland SOM is a time-consuming process. In this study, The effects of applying decomposed straw and woody peat which has the similar structure in soil humic substances on improving SOM contents of newly-reclaimed arable red-yellow paddy soils was investigated. In addition, three commercial activators were used to promote the rapid transformation of straw nutrient, and field experiments were conducted to compare the effects of straw, woody peat and activators application on the yields and soil properties of yellow paddy soils, and meanwhile Pyrosequencing-based analysis of the V4-V5 16S rRNA was used to elucidate its microbial mechanism. The field experiments included six treatments: soil without straw or peat (CK), soil + straw (S), soil + straw + peat (SP), soil + straw +peat + activator I (SPJ1), soil + straw +peat + activator Ⅱ (SPJ2), soil + straw +peat + activator Ⅲ (SPJ3). The results showed that SP, SPJ1, SPJ2 and SPJ3 treatments had the highest SOM, EOC, DOC, MBC and MBC/MBN. The contents of SOM, EOC and DOC of SP, SPJ1, SPJ2 and SPJS treatments were 12.1%-20.6%, 29.9%-48.9%, and 50.8%-75.5% higher than those of S or CK treatment, respectively, while those of MBC and MBC/MBN were 10.5-13.5 and 5.1-12.4 times of those of S or CK treatment, respectively. The content of AvaP and aggregation degree were similar between SPJ1, SPJ2 and SPJ3, and were significantly higher than those of other treatments, increased by 44.7%-63.6% and 26.4%-43.6% respectively compared with S treatment. It showed that peat and all three activators in this research could significantly improve soil physical and chemical properties. The dominant bacteria in paddy soil were Proteobacteria, Acidobacteria and Chloroflexi. Bacterial diversity and phylogenetic diversity index were higher in all stimulator-applied soils and were significantly positively correlated with DOC and EOC, respectively. The bacteria community composition in the soils treated with all three activators were similar and had markedly differences with other treatments. And the differences were mainly related to AvaP, DOC, EOC and MBN. The results above indicated that the addition of activators to paddy soils with straw returning has the potential to stimulate soil microorganisms with nutrient conversion functions, thereby, can improve soil fertility and increasing crop yields, and all three activators selected in this study have similar effects.