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 development (SPAD) values. In each treatment, the growth rates of the crops during the jointing and booting stages were higher than that in the booting to grain filling stage. After two years of land-use, the mean height of the crop in the C50 treatment was 8.16%, 3.32%, 3.31%, 9.86% and 7.55% higher than that for the C30, C40, C60, C80 and C100 treatments, respectively. The differences between treatments were significant (p < 0.05). SPAD values were highest at the heading stage. The highest value for the C50 treatment was 298.41 after two years of land-use. 3) Soil thickness significantly affected yields and the water use efficiency (WUE) of summer maize. The highest average crop yield and WUE value during the experimental period for the C50 treatment were 4614.12 kg hm-2 and 13.57 kg hm-2 mm, respectively. For the C50 treatment the multi-year average water use efficiency was significantly higher than that of the other treatments in 2010–2015. In conclusion, a soil thickness of 50 cm covering the bare exposed rock was adequate as a tillage layer for the crop, and all crop growth indexes in this treatment were better than for other soil thicknesses. The results provide a scientific basis for the land remediation and ecological restoration of bare rock and gravel land. At the same time, for Africa, where one-third of the land is desert, arable land resources are relatively scarce and agricultural ecology is fragile, can serve as a significant reference to improve the ecological environment, develop arable land resources and increase agricultural income.