[Responses of soil microbial biomass C and P to different long-term fertilization treatments in the yellow paddy soil].

To explore the rational fertilization mode to improve the availability of soil phosphorus (P), we analyzed the changes and coupling characteristics of soil carbon (C) and P, microbial biomass C (MBC) and P (MBP) under different fertilization modes with a successive 22-year field experiment in yellow paddy soil. The experiment had 10 treatments, including no fertilization (CK), single application of nitrogen (N), combination of phosphorus and potassium (PK), combination of nitrogen and potassium (NK), combination of nitrogen and phosphorus (NP), combination of nitrogen, phosphorus and potassium (NPK), single application of organic fertilizer (M), and three organic-inorganic fertilizer combinations (1/4M+3/4NP, 0.5MNP, MNPK). The results showed that, compared with CK, the contents of total organic C (TOC), total P (TP), MBC and MBP in N and NK treatments decreased to some extent, while those in PK, NP and NPK treatments increased. Compared with the treatments of no fertilizer and inorganic fertilizer, the contents of TOC, MBC, MBP and MBP/TP ratio in treatments with manure significantly increased, among which M and MPNK treatments showed the strongest enhancement. The treatments with manure had the lowest MBC/MBP ratio, TOC/MBP ratio and MBC/TP ratio, while N treatment had the highest value. MBC, MBP, MBP/TP ratio, MBC/MBP ratio, TOC/MBP ratio and MBC/TP ratio were significantly correlated with TOC and available P, TOC was the direct factor affecting MBC, MBP, and MBP/TP ratio, while available P was the direct factor affecting MBC/MBP ratio, TOC/MBP ratio, MBC/TP ratio. In summary, soil MBP content and the coupling relationship between C and P could effectively distinguish the modes of production with single chemical fertilizer application and manure application, and could be used as biological indices in the evaluation of soil P fertility. Combined application of manure is an effective way to enhance P availability and increase its potential capacity and maintain soil biological health in yellow paddy soil.