Abstract
Organic manure substituting chemical fertilizer is considered as an important agricultural practice for improving crop yields, but it also disturbs the soil biogeochemical cycling. In order to explore the variation of soil properties and bacterial community structure in different fertilization treatments, a field experiment (2011-2017) was carried out in the wheat-rice rotation system with four treatments: control (CK, without any fertilizer), solely chemical fertilizer (NPK), organic manure substituting for 50% of chemical nitrogen (N) fertilizer (NPKM) and 100% of chemical N fertilizer (OM). Results showed that, the highest crop yields (wheat and rice) from 2011-2017 years were all observed in NPKM treatment. Combined with α-diversity analysis, NPKM increased the soil bacterial community richness (supported by the increased indexes of Ace and Chao1) in wheat season, as well as OM treatment in rice season. Compared with NPK, organic manure inputs (NPKM and OM) increased microbial biomass carbon (MBC) content, and encouraged the dominant bacteria (Acidobacteria, Anaerolineaceae and Nitrospira) in both crop seasons. Additionally, NPK significantly promoted the relative abundance of Rhodanobacter in wheat season due to the low soil pH, possibly resulting in the lower crop yield. Similar bacterial composition and structure was found between NPKM and OM treatments in the wheat season. However, application of NPKM significantly increased the relative abundance of Nitrospira in the rice season, which may generate large amounts of nitrate nitrogen (NO₃^--N), and then bring the risk of N₂O emission and NO₃^--N leaching in paddy. We further found that the soil pH and organic matter were the dominant soil characteristics affecting bacterial community structure. Overall, considering the crop yields and soil quality sustainability, organic manure substituting parts of chemical fertilizer was an optimal approach to increase crop yields and reshape soil bacterial community in wheat-rice rotation fields, while more organic manure should be applied in rice season.
 

Wheat-rice rotation system; Organic manure substitution; Bacterial community diversity; Bacterial community composition