35 years of manure and chemical fertilizer application alters soil microbial community composition in a Fluvo-aquic soil in Northern China

- 35 years manure application decreased the ratio of fungi to bacteria.
- 35 years chemical fertilizer addition decreased the ratio of Gram-positive bacteria to Gram-negative bacteria.
- Soil microbes are more responsive to manure application than to chemical fertilizer application.
- The six environmental variables (pH, SOC, TN, TP, IN and AK) explained 61% of the variation in microbial community.

Soil microbial composition is important to soil organic matter decomposition and nutrient cycling. However, our knowledge about how different fertilization regimes could affect soil microbial communities remains limited. In this study, we investigated the long-term (35 years) effects of eight different fertilization regimes: two manure levels (with or without), combined with four chemical fertilizer regimes (no chemical fertilizer, N, NP, NPK) on a range of soil chemical and microbial properties in a wheat-maize/sweet potato double cropping system. Results showed that repeated application of manure or chemical fertilizers significantly increased soil organic carbon and total nitrogen contents, promoted microbial growth and activity, and changed microbial community structure. Annual addition of manure induced a significant decrease of the ratio of fungi to bacteria and a distinct shift in the bacterial community to greater abundance of Gram-positive bacteria compared with Gram-negative bacteria. However, chemical fertilizer additions significantly decreased the ratio of Gram-positive to Gram-negative bacteria. Principal component analysis showed that the impact of manure on microbial community structure was more significant than that of chemical fertilizer. Furthermore, redundancy analysis indicated that the most probable mechanism of the impacts of fertilization practices on microbial community structure may be the mediation of soil C and nutrient availability in this calcareous Fluvo-aquic soil.