1.2.3 Sample determination
Soil samples were air-dried at room temperature, and visible roots and
other debris in the soil samples were removed. Each composite soil
sample was sieved through a 2-mm sieve. SOC was determined by the
Walkley–Black method (Nelson & Sommers, 1996). Total N was determined
by the Kjeldahl acid digestion method (Foss Kjeltec 8400, FOSS, DK)
(Nelson & Sommers, 1996). Total P was measured by Mo-Sb colorimetry
(UV-2102C, UNICO, Shanghai, China) (Nelson & Sommers, 1996). Soil pH
value: potential method (water/soil ratio: 2.5:1). Urease enzyme
activity was measured using the phenol sodium-hypochlorite sodium
colorimetric method (Soil Physics institute, 1978). Sucrase enzyme
activity was calculated according to the amount of glucose (mg) that was
generated in 1 g soil sample after cultivation at 37℃ for 24h (Soil
Physics institute, 1978). Alkaline phosphatase enzyme activity was
determined using the method of disodium phenyl phosphate (Soil Physics
institute, 1978). Catalase was determined by KMnO4titration (Soil Physics institute, 1978).