4WHITBREADA M, LEFROYR D B, BLAIR G J. A survey of the impact of cropping on soil physical and chemical properties in north-western New South Wales [ J]. Australian J of Soil Res, 1998. 36:669-681.
5LEFROV R D B, BLAIR G, STRONG W M. Changes in soil organic matter with cropping as measured by organic carbon fractions and ^13C natural isotope abundance[J]. Plant and Soil, 1993, 155-156:399-402.