Abstract: 【Objective】 The effect of biochar on soil microbial biomass carbon and nitrogen and enzyme activity of Tier soils in the Guanzhong region of China was studied. It may provide a theoretical guidance for biochar to improve soil quality as a soil amendment. 【Method】Biochar used in the field trail was produced by the pyrolysis of fruit tree stems and branches under the condition of 450°C and limited oxygen. Then biochar was mixed with the surface horizon of the soil (0-20 cm) with different dosages (0, 20, 40, 60, and 80 t·hm^-2 which was expressed as B0, B20, B40, B60, and B80, respectively.). After two years of summer maize and winter wheat rotation, the soil biological activity and physicochemical properties of different soil layer was measured. The effect of biochar on soil enzyme activity and microbial biomass carbon and nitrogen in Tier soils was studied by the principal component analysis. 【Result】(1) In the 0-20cm soil layer, the soil microbial biomass carbon (SMBC) and soil microbial biomass nitrogen (SMBN)of the treatments with the 40 or 60 t·hm^-2biochar were higher than those of the other treatments, while in the 20-30cm soil layer, SMBC and SMBN reached the maximum with the treatment of 80 t·hm^-2 biochar, and this principle was true when the biochar amendment and the control was compared. (2) In the different soil layers, the variation regularity of soil enzyme activities were the same, the overall trend was an increase and then decrease with the increase of the amount of biochar. The soil enzyme index (SEI) indicated that the application of biochar significantly increased the SEI. In the 0-10 cm soil layer, compared with the control, the SEI of the treatments of biochar amendment was significantly increased by 1.6-2.7 times. In the 10-20 cm and 20-30 cm soil layers, this index was significantly increased by 26.6%-39.5% and 18.7%-21.7%, respectively. However, SEI was significantly decreased with the increase of biochar to 80 t·hm^-2. (3) By principal component analysis, the eight indexes in this study can be divided into two categories, the soil active factor and the soil strength factor. The comprehensive scores of different soil layers were 0-10 cm >10-20 cm >20-30 cm. In 0-10 cm and 10-20 cm soil layer, the comprehensive scores of different treatments were B60>B40>B20>B80>B0, and in 20-30 cm soil layer, the composite score was B60>B80>B40>B20>B0, respectively.【Conclusion】The application of biochar may lead to the increase of soil microbial biomass, soil enzyme activities, and the soil biological environment. Overall, the treatment with 60 t·hm^-2 biochar led to the best comprehensive performance in this study.

Key words: biochar, soil microbial biomass carbon and nitrogen, soil enzyme activities, soil enzymes index, principal component analysis, tier soil