Wheel traffic effects on tillage draught

Tractor and/or implement wheels precede ground tools, and compact soil immediately before it is loosened in most tillage and planting operations. The work reported here was designed to quantify the impact of preceding wheel traffic on tine draught and the energy requirements of tillage, as part of a programme to assess the benefits of controlled traffic operation. Instrumented tines on a three-point linkage toolbar were used behind a 70 kW two-wheel drive tractor to measure the 'traffic effect' of wheels on the draught of the tillage tools following them in a clay soil. Under conditions broadly representative of Australian grain production, the draught of chisel and sweep tines operating behind tractor or implement wheels was increased by a factor of approximately two, compared with identical tines unaffected by preceding wheel traffic. These data can be used to demonstrate that the traffic effect on trailed tillage implements can increase total draught by more than 30%. This can be defined as the 'traffic penalty' of the operation, and indicates the extent to which a conventional tractor/implement system generates its own workload. A 'traffic efficiency' parameter is proposed to quantify the impact of tractor and implement traffic effects, and used to show that approximately 50% of a tractor's power output can be dissipated in the process of creating and disrupting its own wheel compaction. These results can be used to explain the reduction in tillage energy which occurs in controlled traffic systems, and indicate other approaches to improving overall tractor/tillage system efficiency. They are also the basis of speculation about the relationship between tractive efficiency, traffic efficiency and soil structure damage. (C) 2000 Silsoe Research Institute.