Improvement of Planosol Solum: Part 5, Soil Bin Experiments with a Three-stage Subsoil Mixing Plough

Abstract

A drop-down type plough (two-stage subsoil mixing plough) was effective for the one-to-one mixing of the second (Aw) and third (B) horizons to improve the planosol solum in China leaving the first (Ap) horizon undisturbed. However, this machine had the following disadvantages: (1) it produced large soil clods, (2) it had a large draught requirement, (3) it required a furrow following system, (4) it has poor frame strength, and (5) it was necessary to remove the first plough body to facilitate opening of the first furrow. Basic soil bin tests were conducted in Japan to develop a three-stage subsoil mixing plough to solve these problems using half-size model ploughs. The results showed that the draught requirement and clod size, could be reduced by using three plough bodies; one for the Ap, one for the Aw and one for the B horizons. A slatted mouldboard should be used to minimize draught rather than a plate mouldboard. The optimum working widths of the second and third plough bodies were 150 mm, which minimized draught but resulted in a wider working width than the nominal value.