CK, control with no-tillage and straw removal before maize planting; NT, no-tillage with straw stubbles 30–40 cm in height before maize planting; RT, rotary tillage with straw incorporation before maize planting; SR, straw return after maize harvest; SR0, no straw return after maize harvest. Values followed by different lowercase letters within the same column indicate significant difference at P < 0.05.