Short term effects of biochar with different particle sizes on phosphorous availability and microbial communities

Despite the increasing interest for biochar as a soil amendment, a knowledge gap remains on different particle size of biochar on soil phosphorous (P) availability and its impacts on microbial community. We hypothesized that biochar particle size and incubation temperature can significantly influence soil P availability and microbial community in subtropical acidic soil. A laboratory incubation study was established to investigate the effects of soil pH, available P and soil microbial responses to biochar addition having varying particle sizes using paddy soil and red soil under different incubation temperatures (15 °C & 25 °C). Biochar produced via pyrolysis of spent mushroom substrate feedstock was sieved into three particle sizes ((≤0.5 mm (fine), 0.5-1.0 mm (medium) and 1.0-2.0 mm (large)). The results exhibited that the fine particle biochar resulted in significantly higher release of P, soil pH, available P and bacterial species richness while simultaneously reducing the activities of phosphatase enzyme in both soils. Apprehending the impact of biochar particle size and incubation temperature, principal coordinate analysis (PCoA) predicted that soil microbial communities with fine particle biochar and high incubation temperature (25 °C) clustered separately. Redundancy analysis depicted that fine particle biochar had a direct association with available P and soil pH while high incubation temperature depicted a strong affinity for microbial communities. Hence, it is suggested that fine particle biochar and high incubation temperature may provide better habitat for microorganisms compared to the other particle sizes which may be due to improved soil pH and available P. However, a long term study of different biochar particles application in subtropical acidic soil needs to be pursued further for a more comprehensive understanding on this issue.