Amending biochar affected enzyme activities and nitrogen turnover in Phaeozem and Luvisol

Therefore, we conducted two five-year field experiments in contrasting soils (Phaeozem and Luvisol) with biochar application rate at 0 t·hm-2 (CK, 0), 22.5 t·hm-2 (D1, 1％), 67.5 t·hm-2 (D2, 3％) and 112.5 t·hm-2 (D3, 5％) to investigate the potential effects of biochar application rate on soil organic nitrogen (N) turnover and its linkage to enzymatic mineralization in contrasting soil. The results showed that soil organic carbon (SOC) and microbial biomass nitrogen (MBN) contents, microbial biomass carbon to nitrogen ratio (MBC:MBN) and protease activity are significantly influenced by biochar application rate whereas not by soil type. Ammonium nitrogen (NH4+-N) and nitrate nitrogen (NO3--N) contents, and dehydrogenase (DHA) activity are significantly changed by soil type whereas not by biochar application rate. Based on the redundancy analysis (RDA), we found that organic N fractions are associated with MBN, SOC and protease in Phaeozem, but related to protease activity in Luvisol. Our findings indicated that organic N turnover is not only related to the bioavailability of N but also requires carbon substrates in Phaeozem, whereas the transformation of organic N in Luvisol is dominated by enzymatic mineralization as the relatively low level of bioavailable N.