2.4 Statistical analysis
Statistical analyses were performed using the R i386 3.3.1 (R Development Core Team) software package. The t-tests were used to compare grassland and cropland at same soil layer in all sites on SOC, STN, STP, C:N ratio, NH4+_N and NO3-_N, soil aggregations, soil microbial biomass, microbial relative abundance and F:B ratio. Three-way ANOVA was used to test for significant differences among site, land use, soil depth and their interactions on the soil microbial biomass. Correlation analysis were conducted to identify the soil parameters accounting for the soil microbial biomass.