The basis of tractor power selection on arable farms

Abstract Primary tillage largely dictates the power requirement on an arable farm. The effectiveness of the power and machinery system is, however, arbitrarily determined by the management skill in matching work output to the time available at an acceptable level of fixed and variable costs. The farmer tends to compensate for inadequacies of the machinery system and for vagaries of the weather by adjusting the definition of soil workability and amending the time available to suit the advanced or belated state of progress in the field. The identification of the effect of different soil moisture content levels on the work rate of various tractor-plough combinations provides a more objective assessment of soil workability and represents a major advance on existing machinery planning procedures. It has been achieved by relating traction and plough draught to cone index as a soil strength parameter which is soil moisture dependent. Incorporating a soil moisture simulation model, this study shows the feasibility of a comprehensive computer program for the selection of tractor-plough combinations for a given climate and soil type within a machinery, labour and timeliness penalty cost framework.