TILTH MELLOWING

Summary Effects of weathering action, mainly wetting and drying cycles, on the strength of the clods produced by tillage are studied. Experiments were carried out on sandy loam soils at two sites in South Australia, and on silt loam and clay soils at Wye College, England. It is found that tillage increases the amplitude of soil water content fluctuations. These bigger soil water content fluctuations resulted in a decrease in the clod strength and this in turn modified the size distribution of the clods produced by tillage in the South Australian soils. The decrease in clod strength, as measured by the drop shatter test, was followed by an increase in the proportion of the smaller aggregate size fraction produced by a second implement pass. It is suggested that, for soils in which the increase in the soil water content fluctuations after the first tillage implement pass decreases clod strength, a further implement pass should be delayed for several days. By doing this, the soil can be tilled with minimum energy and cost to produce a good seed bed.