Animal manures are reported as good substitutes for chemical fertilizers to mobilize soil phosphorus (P). However, the mechanisms on how different types of manures regulate microbial biomass involved in P mobilization remain unclear. In this study, we conducted a two-year field experiment to investigate variations in soil microbial biomass carbon (MBC) and P (MBP) and P fractions after 30% animal manures substitution (pig manure (PM), chicken manure (CM), and dairy manure (DM)) in paddy soil. Furthermore, a 30-day incubation experiment was used to explore the mechanisms of soil P transformation induced by 100% manures addition. Two-year field experiment results showed that, compared to the chemical NPK fertilizer, 30% manure substitution didn't influence rice and wheat yields significantly but decreased soil total P loss from runoff by 3.2%. However, 30% manure substitution significantly enhanced MBC and MBP by 11.3-18.4% and 57.1-81.2%, respectively, which also promoted the transformation of moderately labile P (M-P) to labile P (L-P). Moreover, the incubation experiment also convinced that all manures caused higher MBC than chemical P fertilizer. Meanwhile, compared to the no P fertilizer, manures increased L-P and organic P by 2.7%-14.7% and 6.4%-20.0%, respectively. Redundancy analysis indicated that soil MBC/MBP ratio was the main factor to soil L-P and M-P, indicating that animal manures can improve soil microbial abundance and thus promote M-P to L-P in soil. Among three animal manures, PM could improve the mobilization potential of P mostly, due to the highest C source activity by 13C NMR analysis. Our study indicated that animal manures especially PM can be considered as a good candidate for agricultural P management in paddy soils because of their capacity to promote soil P transformation.
Keywords: Animal manures; Microbial biomass; Microbial community; Paddy soil; Phosphorus transformation.
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