Effects of amendment of different biochars on soil enzyme activities related to carbon mineralisation

This study aimed to investigate the effects of different biochars on soil enzyme activities associated with soil carbon (C) mineralisation. Biochars were produced from two types of feedstock (fresh dairy manure and pine tree woodchip) at temperatures of 300°C, 500°C, and 700°C. Each biochar was mixed at a ratio of 5% (w/w) with a forest loamy soil and the mixture was incubated at 25°C for 180 days. Soil mineralisation rates, soil dissolved organic C, soil microbial biomass C, and five soil enzyme activities were measured during different incubation periods. Results showed that biochar addition increased soil enzyme activities at the early stage (mainly within the first 80 days) because biochar brought available nutrients to the soil and increased soil dissolved organic C and microbial activity. Soil enzyme activities were enhanced more by the dairy manure biochars than by the woodchip biochars (P < 0.05). The enhancement effect on enzyme activities (except catalase activity) was greater in the treatments with biochars produced at lower pyrolysis temperature (300°C). Linear relationships between some soil enzymes and C-mineralisation rates might indicate that the increased enzyme activities stimulated soil C mineralisation at the early stage. However, the biochar additions could result in great C sequestration in the long term, especially for the woodchip biochars pyrolysed at higher temperatures.