7Hayder G, Mumtaz S S, Khan A, et al. Maize and soybean intercropping under varies levels of soybean seed rates [J]. Asian Journal of Plant Science, 2003, 2(3) : 339-341.
8Jaynes D B, Swan J B. Solute movement in uncropped ridge tilled soil under natural rainfall [J]. Soil Science Society of America Journal, 1999, 63: 264-269.
9Ito O, Johansen C, Adu-Gyamfi J J, et al. Roots and Nitro gen in Cropping Systems of the Semi-arid Tropics [M]. In- ternational Research Center for Agricultural Science, 1996: 481-492.