9Kapusta G. , et al. Com yield is equal in conventional, reduced, and no tillage after 20 years. Agronomy Journal, 1996, 88 (5) : 812 - 817.
10Ike L. F, Soil and crop response to different tillage practices in a ferruginous soil in the Nigeria savanna. Soil and Tillage Research, 1986,6:261 - 272.