Improvement of Whitish Oasis Soil, Part 2: Preliminary Soil Bin Experiments with a Four-stage Subsoil Inverting Plough

Abstract

The objective of this work was to develop a special machine, a four-stage subsoil inverting plough which would improve the permeability of whitish oasis soil by inverting the second horizon (Bca) and the third horizon (C) underground and by lowering the percentage of calcium carbonate (CaCO 3) in the subsoil horizon. Specifically, the Bca horizon (with its high content of CaCO 3) is lowered, and the C horizon (with less CaCO 3) is raised. This paper describes the results from preliminary soil bin experiments, that were conducted in Japan with half-scale model ploughs. Optimum shapes of the third and fourth plough bodies were determined for a full-scale four-stage subsoil inverting plough. The results show that a fold-up type plough body with a window on the mouldboard is effective for the inversion of the Bca and C horizons. The optimum approach angle of the third and fourth plough bodies, which is the angle with respect the travel direction, was 30°. The optimum window height of the third plough body was 0 mm, so that the third plough body had no window, and the plough body cut into the soil halfway up the middle of the body. This design gave the smoothest flow of soil. The optimum window height of the fourth plough body was 130 mm. The draught requirements of the plough body were such that the draught to cut soil was the largest, followed by the draught of the accumulated soil block, then by the draught caused when the soil was folded up and finally by the draught caused when the soil slid horizontally on the mouldboard. When the soil water content was 10·5% and 16·9% d.b., the soil inverting rate was an average of 0·9. Nearly perfect inversion of the Bca and C horizons could be obtained because the soil water content was less than the plastic limit (23·7% d.b.), and the soil was easily broken into small pieces that flowed smoothly over the plough body. However, when the soil water content was 25% d.b., which was greater than the plastic limit, the soil inverting rate decreased, and soil did not flow smoothly over the plough body.