2.3 | Soil sampling and analysis
After maize harvest, twelve soil samples were randomly collected from
the topsoil layer (0–20 cm) in each plot in October every year. The
fresh soil samples from each plot were mixed as a composite sample,
air-dried, finely ground, and sieved to pass through a 0.15 mm mesh. The
SOC was determined using
K2Cr2O7–H2SO4digestion method (Bao, 2000), and the measurement of SOC stocks was
based on a constant soil mass (Xu et al., 2019).