2.4 Soil physicochemical properties
The air-dried soil samples were sieved through soil sieves with 2 mm, 1
mm and 0.25 mm aperture, and four groups of soil samples were obtained
(>2 mm, 2-1 mm, 1-0.25 mm, <0.25 mm)
(Muruganandam, Israel , & Robarge, 2009),
use an electronic balance to
weigh the weight of each particle size.
The soil structural stability was
evaluated by the mean weight diameter (MWD) of water-stable aggregate
(Zhao, Chen, Hu , & Li, 2017). The content of easily extractable
glomalin-related soil protein (EE-GRSP) and total glomalin-related soil
protein (T-GRSP) was determined by improving the assay method according
to Janos et al. (2008). The EE-GRSP was extracted from 0.5 g soil with 4
ml of 20 mmol L-1 of sodium citrate (pH=7.0) and
autoclaved at 121℃ for 30 min. The T-GRSP was extracted from 0.5 g soil
with 4 ml of 50 mmol L-1 of sodium citrate (pH=8.0)
and autoclaved at 121℃ for 60 min.
The supernatant was collected by centrifugation at 10000 rpm for 10 min
at 4℃. The T-GRSP extraction was performed 6 times until the solution
was straw-colored ((Gao, Zhou, Ling, Hu , & Chen, 2017). An
spectrophotometer (595 nm) was used to determine the GRSP content using
bovine serum protein as the standard product.
The rest air-dried soil samples were used to determine soil pH by pH
meter (FiveEasy FE20) on a mixture of water to soil ratio of 2.5:1.
TC (total carbon), TOC (total
organic carbon), and total N (TN) were determined by the analyzer (multi
N/C 2100 TOC/TN Analyze, Germany, Analytikjene). Soil ammonium N
(NH4+-N) and nitrate N
(NO3--N) were determined by continuous
flow analyzer (BRAN+LUEBBEAA3, Germany), and the extract solution was 2
mol·L-1 KCl, and soil total phosphorus (TP) and
available phosphorus (AP) were determined by the molybdenum antimony
anti-colorimetric method.