| The correlation between soil biological activities and soil fertility was studied after different amounts of biochar were applied. The correlation analysis results showed that soil biological activities, not including invertase activity and oil microbial biomass carbon, were negatively correlated with soil bulk density. There were significant correlations between soil urease and catalase activity, soil microbial biomass nitrogen, the quantities of microbes and soil chemical and physical factors. Except for invertase activity, the soil enzyme activities showed a positive correlation with the quantities of microbes. But the relationships between four soil enzyme activities were not totally significant. Path analysis showed that the soil urease and microbial biomass nitrogen played a predominantly direct role in soil fertility, while the catalase activity mainly provided an indirect contribution. According to the results of Principal Components Analysis (PCA), soil fertility could be described by microbe factor, enzyme activities factor, and available phosphorus factor. Soils after maize harvest had higher comprehensive score than those after wheat harvest. The comprehensive score of different treatments was escalated with the increase of biochar application rate, which indicated that high rate of biochar would have a more significant effect on improving soil fertility. |