IMPROVEMENT OF PLANOSOL SOLUM .5. SOIL BIN EXPERIMENTS WITH A 3-STAGESUBSOIL MIXING PLOW

A drop-down type plough (two-stage subsoil mixing plough) was effectiv e 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 str ength, and (5) it was necessary to remove the first plough body to fac ilitate opening of the first furrow. Basic soil bin tests were conduct ed in Japan to develop a three-stage subsoil mixing plough to solve th ese problems using half-size model ploughs. The results showed that th e draught requirement and clod size, could be reduced by using three p lough bodies; one for the Ap, one for the Aw and one for the B horizon s. A slatted mouldboard should be used to minimize draught rather than a plate mouldboard. The optimum working widths of the second and thir d plough bodies were 150 mm, which minimized draught but resulted in a wider working width than the nominal value. (C) 1996 Silsoe Research Institute.