9Lal R. No-tillage effects on soil properties under different crops in Western Nigeria[J]. Soil. Sci. Am. J, 1976,40 : 762-768.
10Blevins R L, Thomas G W, Smith M S, et al. Changes in soil properties after 10 years continuous nontilled and convertionally tilled corn[J]. Soil and Tillage Research, 1983,3 (2) : 135-146.