Effects of organic substitution for synthetic N fertilizer on soil bacterial diversity and community composition: A 10-year field trial in a tea plantation

Substitution of chemical nitrogen (N) with organic fertilizers in agricultural ecosystems has been promoted to sustain crop yield and soil quality. Soil microbes play key roles in soil nutrient cycling after organic matter addition. However, there is limited information about the effect of the organic substitution ratio (OSR) on soil bacterial communities, which are considered as a good indicator of soil quality in a tea plantation. In this study, a long-term field experiment with six treatments was established to study the effect of different OSRs of N, from pure synthetic fertilization (NPK) to 100% N substituted with organic fertilizer (OM100), on tea yield and soil bacterial communities. The soil bacterial community composition was measured using a high-throughput sequencing technique. The results showed that as the OSR increased, the soil bacterial diversity increased and the community structure shifted significantly. However, 25% N substituted with organic fertilizer (OM25) produced the highest yield. Additionally, the soil pH and organic carbon (SOC) were the predominant soil characteristics that accounted for the soil bacterial community structural change. With more chemical N being substituted with organic fertilizer, the soil pH, available potassium, SOC, total N, and microbial biomass C and N, were elevated; however, the yield of fresh tea leaves decreased. These results indicated the trade-off effect between tea yield and soil bacterial diversity under different OSRs, which could also alter the soil bacterial communities by changing soil characteristics.