Because of fuel consumption, machinery and labor costs, tillage involves high expenses. In a project that was carried out in the autumn of 2001 and 2002, energy consumption and draught were studied for three tillage implements on a lighter and a heavier soil under wet, moist and dry conditions. Furthermore, aggregate size distribution and energy requirement for fracturing the soil were measured. The tillage implements used were mouldboard plough, chisel plough and disc cultivator. The effects of driving speed and depth of tillage were also studied. Soil strength was measured with both a penetrometer and a shear vane apparatus. The tractor used was a Valmet 6600 (100 hp) with equipment for measuring fuel consumption. The equipment was calibrated to give the PTO effect for any combination of fuel consumption and engine speed, and this was assumed to be the same as the effect available at the tractor wheels. The “tow bar power” was calculated by subtraction of power losses through wheel slip and rolling resistance. Average actual working depth was calculated by measuring bulk density before tillage and then weighing the cultivated soil. On the basis of the tillage depth and PTO effect measurements, it was possible to calculate energy requirement per kg cultivated soil and specific draught. The latter is defined as force per cross sectional area cultivated soil [kN/m2]. After sieving samples of the cultivated soil, the approximate surface area of the fragmented soil and the energy requirement for fracturing were computed. Specific draught was lowest for the mouldboard plough, while the highest values were obtained for the chisel plough. Specific draught decreased with increasing soil water content. The lowest values of energy requirement for fracturing were measured under moist conditions for all tillage implements, and the disc cultivator produced the highest fracturing in relation to energy input. Both specific draught and energy requirement for fracturing were lower for the lighter soil. With the disc cultivator, specific draught increased with working depth, while depth had no influence on specific draught when the mouldboard plough was used. Some of these differences can be explained by differences in geometry between the tools. There was a tendency for specific draught to increase with increased driving speed. This was most obvious on the lighter soil and for the mouldboard plough. The increased draught can be explained by a higher acceleration of soil particles and by increased soil strength because of higher deformation rate. Soil strength and thereby draught requirement differed between soils and moisture contents. There was a strong correlation between soil cohesion and draught requirement, and cohesion was easily measured in the field with a shear vane. The penetrometer measurements did not correlate with draught measurements. Specific draught was lowest for the mouldboard plough. When considering the overall results of tillage, no one implement can be identified as being the most effective. Tillage at water content close to the plastic limit seems to be a good compromise as regards draught requirement and tillage result.
展开▼
