Effect of biogas slurry addition on soil properties, yields, and bacterial composition in the rice-rape rotation ecosystem over 3 years

Purpose: Organic treatments may improve soil nutrient availability and ecological functions. This study aimed to determine the effect of biogas slurry (BS) on soil properties, yields, and bacterial community activity and to examine the main environmental factors impacting bacterial compositions in the ecosystem. Materials and methods: A 3-year field experiment was conducted in yellow soil under a rice-rape rotation to understand the effect of BS originating from anaerobically digested pig waste on soil chemical and bacterial compositions. Results and discussion: Compared with an inorganic nutrient treatment and a control, adding BS at a moderate dose (BS6, 165.1 t ha(-1)) positively affected the rice and rape yields, soil fertility, and bacterial diversity. The BS was more suitable than chemical fertilizer for maintaining agricultural soil sustainability, especially the BS6 and BS7 treatments (165.1 and 182.1 t ha(-1), respectively), by improving nutrient content, increasing soil pH, and promoting soil crumb structure formation. The relative abundance of Actinobacteria in BS6 was decreased by 37.9% compared with the untreated soil and 27.7% compared with the fertilizer treatment, while the relative abundance of Nitrospirae in BS6 increased by 41.2% and 43.5% compared with these treatments, respectively. Redundancy analyses (RDA) showed that pH, rape yield, cation exchange capacity (CEC), and total nitrogen (TN) were significantly correlated with soil bacterial community composition and explained 56.0%, 46.4%, 43.2%, and 34.9% of the total community variability, respectively. The soil bacterial diversity depended mainly on soil pH, and crop rotation played an important role in changing the bacterial community. Conclusions: The soil bacterial composition was clearly altered after 3 years of BS treatments. These increases in bacterial diversity could be of ecological significance in maintaining soil fertility and functionality.