2.3. Laboratory analysis
The BD was determined by drying method of oven-dried at 105℃ for 24 h to constant weight. The contents of WSA were determined by wet sieving method using soil aggregate analyzer (TTF-100, Shunlong experimental instrument factory, Shanghai, China). The enzymatic activities were determined by Deforest method for β-1,4-glucosidase (βG), β-1,4-N-acetyl-glucosaminidase (NAG), L-leucine aminopeptidase (LAP), and acid phosphatase (ACP) (Deforest, 2009). The contents of NH4+-N and NO3--N in soil were determined by continuous flow injection analyzer (AA3-A001-02E, Germany), after extracting 3 g of fresh soil sample with 25 ml 1 mol L-1 KCl solution for 30 min. Soil hydrogen ion concentration (pH) (water-soil ratio of 2.5:1) was determined by pH meter (Sartorius PB-10, Germany). Soil electrical conductivity (EC) (water-soil ratio of 5:1) was determined by conductivity meter (DDS-307, Shanghai, China). Soil total carbon (TC) contents were determined by element analyzer (ECS4024, Italy), after wrapping 0.2 g of dry soil sample screened 0.15 mm sieve with tin paper. The contents of soil organic carbon (SOC) and soil total nitrogen (TN) were determined by potassium dichromate external heating method and Kjeldahl method, after weighing 0.1 g and 1 g of dry soil sample screened 0.15 mm sieve, respectively. Soil total phosphorus (TP) contents after digesting 0.5 g of dry soil sample screened 0.15 mm sieve by HClO4-H2SO4 and adjusting pH and soil available phosphorus (AP) contents after extracting 2 g of dry soil sample screened 2 mm sieve with 40 ml 0.5 mol L-1 NaHCO3 solution for 30 min were determined by Mo-Sb colorimetric method with ultraviolet spectrophotometer (UV-5500, Shanghai, China) at 700 nm wavelength (Zhang et al., 2019c).