[Effects of different types of biochar on phosphorus and stoichiometric characteristics of extracellular enzymes in paddy soil].

Understanding the stoichiometric characteristics of phosphorus and extracellular enzyme activity in paddy soil under the application of different types of biochar can improve phosphorus management and nutrient utilization efficiency. A two-year field experiment was conducted with treatments including no fertilization (CK), chemical fertilizer (NPK), and biochar amendments based on NPK: perishable organic waste biochar (WB), rice straw biochar (SB), and pig manure biochar (MB). Combined with enzyme vector analysis, we explored the effects of different biochar types on soil phosphorus availability and microbial carbon, nitrogen, and phosphorus-related enzyme activities. Results showed that the NPK treatment increased total phosphorus, available phosphorus, and crop yield by 39.8%-73.1%, 128.5%-131.0%, and 27.0%-33.9%, respectively. Compared to NPK, all three biochar treatments consistently elevated soil total phosphorus, with MB>WB>SB, where MB significantly increased by 108.8% and 156.0%. The MB treatment enhanced soil available phosphorus and phosphorus activation capacity by 297.1%-388.4% and 53.3%-143.1%, respectively, leading to average annual improvements of 12.1% in rice yield and phosphorus use efficiency. Biochar application boosted β-glucosidase (BG), N-acetyl-β-glucosaminidase (NAG), and leucine aminopeptidase (LAP) activities by 43.9%-90.4%, 15.7%-77.6%, and 84.5%-173.4%, respectively, but inhibited alkaline phosphatase (ALP) activity by 41.8%-54.9%. Soil enzyme carbon-phosphorus ratios in biochar treatments were significantly higher than in NPK, while carbon-nitrogen ratios were lower. Biochar application effectively alleviated microbial phosphorus limitation and may have shifted to nitrogen limitation. There were significant positive associations between soil total phosphorus and available phosphorus with BG, LAP activity, rice yield, and phosphorus use efficiency, but negative associations with ALP activity. In summary, biochar application enhances soil phosphorus availability and extracellular enzyme activity, mitigated microbial phosphorus limitation, an increased rice yield. The MB performed the best.