Subsequent effects of slag and biochar application on soil carbon pools and soil microoganisms in paddy fields

Using the Fuzhou Plain paddy as the research area, biochar, slag, and biochar + slag(mixed application) were applied to the paddy before the transplantation of early and late rice seedlings in 2015. A no amendment treatment was used as a control. To understand the subsequent effects of the treatments, the soil organic carbon content and the number of fungi and bacteria were tested for during the rice jointing and maturity stages of the early and late paddy fields in 2017. The results showed: The soil organic carbon(SOC) content of the three applied treatments was significantly higher than that of the control group(P < 0.05). However, there was no significant difference among the treatments in dissolved organic carbon(DOC), easily oxidized carbon(EOC), and soil microbial biomass carbon(MBC)(P > 0.05). Compared with the control group, each application treatment group showed an increase in the number of fungi and bacteria in the soil to some extent; however, the difference was not significant(P > 0.05). There was a significant negative correlation between the number of bacteria and DOC(P < 0.01), a significant negative correlation with EOC(P < 0.05), and a significant positive correlation with MBC(P < 0.05). The fungal/bacterial ratio was significantly positively correlated with the number of fungi and DOC(P < 0.01). This showed that improvement in the stability of carbon storage in paddy soil and the increase in the number of soil microorganisms still occurred 2 years after the application of slag and biochar.