Bulk soil samples were taken by using a spade in the cultivated
horizon (Ap, 0–150 mm) fromfive sites in each plot after the
harvest of second rice in 2011. The soil samples were mixed to
obtain a composite sample, which were manually separated into
20–40 mm aggregates along the natural failure surfaces after being
air-dried to the plastic limit. After air drying, part of the soils was
ground to pass a 0.25-mm sieve to measure SOC concentration by a
wet oxidation method with K2Cr2O7 and concentrated H2SO4