The author considered that ploughing deeper and corn residues might form " flat type " boundary soil ( depth = 30cm ) . this kind of profile morphological characteristics could evidently increase the com yields and prevent the erosion of soil 在三角坐标图中,不同形状界面构造土壤的三相组成分布区域是特征性的,因此,我们认为土壤三相组成特征可以作为评价土壤肥力退化的依据。