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).