ENERGY-REQUIREMENTS AND DEPTH STABILITY OF 2 DIFFERENT MOLDBOARD PLOWBOTTOMS IN A HEAVY CLAY SOIL

A field experiment was conducted in Saint-Simon (Quebec) on heavy clay soil to establish the difference in energy requirements and plowing d epth stability between two plow bottom shapes commonly used. The exper imental design was a split-split plot with two bottom shapes, five plo wing depths and five speeds. The helical (long) bottom featured lower share and moldboard approach angles than the cylindrical (short) model and it was equipped with a sharepoint and a longer landside. Results indicate that the long bottom reduced the specific draft force (D-s) b y 12% and the fuel consumption by 6% relative to the short model. D-s had a non-linear behavior with plowing depth for both models. Speed ha d only linear effects on D-s for the long model whereas the short bott om displayed both linear, and cubic trends. Plowing depth standard dev iation (SD) increased as plowing depth decreased for both bottoms. Thi s trend was less significant for the long bottom. However, the average d coefficient of variability (CV=SD/mean) for both bottoms increased f rom 5% to 14% as plowing depth decreased from 220 mm to 140 mm. These results indicate the depth stability problems encountered at plowing d epths less than 150 mm.