SOIL AND CROP RESPONSES TO ZERO-TRAFFIC AND CONVENTIONAL-TRAFFIC SYSTEMS FOR WINTER BARLEY IN SCOTLAND, 1982-1986

An experimental zero-traffic system was compared with a conventional-traffic system over four seasons in Scotland for both ploughed and direct-drilled winter barley seedbeds. A mouldboard plough was used for primary cultivation in both zero- and conventional-traffic plots in the first season, but a chisel plough was used in the ploughed treatments in subsequent seasons. After mouldboard ploughing in the first season, all wheels of both zero-traffic systems were restricted to permanent wheel tracks and all crops were sown in the bed between them. The crop yield for the ploughed zero-traffic system was never exceeded, although in the second season all yields were similar. Overall mean yield decreased with increasing rainfall in the spring and with decreasing soil permeability to air close to the soil surface. Soil compaction by wheels depressed plant populations under direct drilling in wet autumns, especially below wheel tracks in the direct-drilled conventional traffic system. Compaction also occurred in the absence of traffic under direct drilling. Vertical migration of earthworms was assumed to be responsible for some soil structural improvement at depth and, hence, successful direct drilling for both traffic systems, but after wet seasons crop establishment may also require shallow cultivation prior to drilling. After the fourth harvest, the draught force for primary cultivation averaged 17% more for each conventional-traffic system than for the corresponding zero system. © 1990.