Effects of long-term straw returning on rice yield and soil properties and bacterial community in a rice-wheat rotation system

Crop straw returning to the field is an important practice improving soil quality and nitrogen (N) supply. However, little information is available whether and how long-term both wheat and rice straws returning to the paddy field affects rice yield and soil properties and bacterial community in a rice-wheat rotation system. The objectives of this study was to test the hypothesis that soil bacterial communities would regulate soil N mineralization and immobilization turnover during the rice growth season after long term straw returning, and to investigate the relationships of soil physiochemical characteristics and bacterial community with N availability in the soil and rice yield. An indica-japonica ‘super’ hybrid rice (O. sativa L.) cultivar was field-grown and the experiment began in the rice season of 2015 in a rice-wheat rotation system, with four types of straw returning treatments including no straw returning (CK), previous wheat straw returning before rice transplanting (WR), previous rice straw returning before wheat sowing (RR), and both rice and wheat straws returned to the field (DR). The data in this paper were mainly presented in the rice season of 2019 and 2020. Compared with that in CK, on average grain yield was increased by 8.1 %, 7.1 %, and 12.2 % in WR, RR, and DR treatment, respectively. Both physiochemical traits and bacterial communities were responsible for the variation of N uptake at the main growth stages of rice. The total N uptake, especially N uptake rate around the panicle initiation stage was improved in straw returning treatments with largest effect in DR, followed by WR, and RR. The higher N uptake is pivotal for spikelet differentiation and contributed to a larger panicle size and a higher grain yield. N uptake was positively correlated with soil organic carbon content, soil microbial biomass carbon and N content, and soil inorganic N content, but negative correlated with soil pH and bacterial community compositions. Bacterial of Proteobacteria, Bacteroidetes, Nitrospirae, and Chloroflexi were the dominated phyla and were contributed to the differences in bacterial community compositions among the treatments. The long-term straw returning to paddy field could synchronize available N supply in the soil and the demand of rice plants by regulating the dominant bacterial phyla in the soil, and consequently, increase grain yield of rice. This study provides new insights into the mechanism underlying the N cycling driven by bacterial community after long term straw returning and useful information to improve both soil quality and rice yield in a rice-wheat rotation system.