Compaction of a swelling clay soil by agricultural traffic; effects upon conditions for growth of winter cereals and evidence for some recovery of structure

A swelling stagnogley soil remained unwheeled or was uniformly wheeled by a combine harvester and a tractor in two successive autumns before direct drilling winter cereals. Combine wheeling of the soil at its wettest condition caused the largest loss of soil porosity. The autumn and spring of the second growing season for the winter cereals were wetter than long term average. The smaller porosity in the wheeled soil, created lower soil redox potential and smaller oxygen flux as well as greater soil strength and larger amounts of available water, but little difference in soil temperature. The crop in the wheeled soil had fewer plants, less root and a lighter yield than in the unwheeled soil. The wheeled soil recovered some porosity and lost strength after wetting and drying during the second growing season, whereas soil freezing had very little effect. This restructuring was sufficient to reverse some of the detrimental effects of compacting the soil.