2.3 Soil properties
Soil subsamples were air-dried and analyzed for chemical and physical
parameters. Soil pH was determined in deionized water (soil : water, 1 :
2.5) using a pH meter (Mettler-Toledo, Switzerland)). Total SOC was
measured by wet digestion with 133 mmol L-1K2Cr2O7 and concentrated
H2SO4 at 170–180 ℃ Total N (TN) was
determined using a semi-micro-Kjeldahl method. Available N (AN) was
analyzed using a diffusion method. available P(AP) was extracted using a
mixed solution of 0.03 mol L-1 NH4F
and 0.025 mol L-1 HCl. Available potassium (AK) was
determined by flame photometric method. Soil inorganic N
(NH4+ and
NO3−) was extracted from soil samples
with 1 M KCl and determined by colorimetrically using a segmented flow
auto analyzer (Skalar, Breda, Netherlands) (Lu, 1999). The values ofδ 13C and δ 13N were
determined using an isotope ratio mass spectrometer (IsoPrime
100,Germany) coupled with an auto elemental analyzer (vario MICRO
cube,Germany).