3.1. Effects of long-term field treatments on soil properties
The 15-year BF and 23-year BF+ treatments significantly decreased soil C and N contents, but did not significantly affect the C/N ratio compared with the OF treatment (P < 0.05, Table 1). Soil clay content was lower in the BF and BF+ treatments in comparison with the OF treatment, and soil silt content was higher in the BF+ treatment than that of the OF treatment. Furthermore, the BF and BF+ treatments significantly decreased soil DOC content, and the BF+ treatment significantly reduced DOC/TC ratio compared with the OF treatment. It implies lower active C (DOC) content in the BF and BF+ soils due to the long-term removal of plant inputs. Although soil pH of the BF and BF+ treatments and soil WHC of the BF+ treatment were significantly lower than those of the OF treatment, the differences among soil pH did not exceed 0.3 units and the differences among soil WHC did not exceed 1%.