Effect of Covering-Soil Thickness on Crop Growth on Bare Rock and Gravel Land in an Ecological Restoration Project

Abstract: To study the mechanism by which the thickness of covering soil effects crop growth in an ecological restoration project of bare rock and gravel land, the physiological characteristics of summer maize were observed during 2010–2015. This experiment was set up on exposed rock land, which had been covered by soil with six different thicknesses: 30 (C30), 40 (C40), 50 (C50), 60 (C60), 80 (C80) and 100 cm (C100). During the experiment, soil physical properties and the physiological traits and yields of crops were recorded. The results indicated several effects. 1) With the same thickness level, soil bulk density of the covering soil increased in successive planting years. There was a logarithmic relationship between soil bulk density and covering thickness. There was also a strong algorithmic relationship between covering thickness and sedimentation coefficient (R2=0.91). 2) The thickness of covering soil had a significant influence on both the height of summer maize, and soil and plant analyzer deve...