Rice husk biochar impacts soil phosphorous availability, phosphatase activities and bacterial community characteristics in three different soil types

To assess the effects of rice husk biochar (400 °C, 0.5 h) on the conversion of soil phosphorus in different soil types in China, a nine week microcosm incubation experiment was performed using acid red soil, organic brown soil, and saline soil, which were amended with 0, 10, 20 and 40 t/hm2 biochar. Soil physico-chemical properties, microbial biomass, phosphatase activities, phosphate solubilizing bacteria, and bacterial community characteristics were investigated. The results showed that rice husk biochar significantly modulated the pH of the three studied soils by 0.1-0.2 units and increased the soil gravimetric water content by 0.3-1.4% over that of the controls. The addition of biochar significantly enhanced the Olsen-P and microbial biomass carbon in all studied soils, and this was partly dependent on the rate of biochar application. The levels of soil microbial biomass phosphorus and phosphatase activities were most significantly increased with 20 t/hm2 biochar treatment. These results showed that treatment with rice husk biochar could provide more suitable growth conditions for soil bacteria and significantly enhance soil phosphorus availability and related enzymes. Furthermore, bacterial communities were investigated in all three soils using Illumina MiSeq pyrosequencing to generate tentative taxonomic assignments, which differed statistically over time. The results of a heat map with principal component analyses suggested that the biochar tended to shape the structure of bacterial communities in degraded soils such as acid red soil and saline soil. The most significant variation could be observed in the acid red soil. Biochar increased the relative abundance and distribution of Thiobacillus, Pseudomonas, and Flavobacterium in soils by varying degrees; all three are reported to be genera of phosphate solubilizing bacteria. In conclusion, biochar had a positive effect on phosphate solubilizing bacteria and contributed to increasing phosphorous availability.