REDUCTION OF TRAFFIC-INDUCED SOIL COMPACTION - A SYNTHESIS

This paper provides a synthesis of the field traffic and tillage experiments carried out in Germany, Scotland, the Netherlands and England reported in this special issue. The experiments were designed to investigate interactions between traffic-induced soil compaction, cropping and the design of machinery and its management in the field. Treatments included reduced ground pressure and zero traffic, and conservation tillage. Where zero traffic was employed, yields of sugar beet, potatoes, onions and ryegrass increased in the range 4-14%, compared with conventional practice. Yield responses from wheat and barley were variable, being either negative or positive in the range -9 to +21% compared with a conventional system. Conservation tillage techniques were used without compromising yield, but needed to be timed appropriately within a given rotation. In all situations where zero traffic was employed, soil porosity was maintained and soil strength and density were significantly reduced compared with conventional practice. Primary and secondary cultivations had a lower draught and energy requirement (in the range 37-70%) under this regime and fewer and less intensive operations were required to produce a seedbed. Responses to the reduced ground pressure systems were generally intermediate between those from conventional and zero traffic. The use of additional wheels or alternative tyres to maintain inflation pressures at or below 80 kPa was only practical for axle loads of up to about 10 mg. A 74 kW, 12 m span two wheel-drive gantry was found to be a practical method of introducing a zero traffic system to a minimum tillage cereals farm. High-draught operations could not be performed on a practical scale, however. A simple formula was derived, using vertical wheel loads and tyre inflation pressure, to predict the maximum stress produced in the soil under wheels. An analysis of the nature of vehicle passes over field soils showed that the greatest potential for damage occurs during tillage and the harvesting of root and forage crops.