Drilling vegetables into autumn-cultivated soil with a low ground pressure vehicle: effects on timeliness and soil compaction

Secondary cultivations for the spring-sowing of vegetables are often delayed because they cannot be carried out until the soil to the depth of cultivation has dried to the plastic limit (i.e. it crumbles rather than smears). It is suggested that doing secondary cultivations in the autumn, and then drilling in the spring without further cultivation, would be less liable to delays because only the soil down to the depth of drilling need dry below the plastic limit. Simple models are derived to calculate soil water contents from weather data. They show that between 1960 and 1981 the 0–120 mm layer (representing a typical cultivation depth) dried beyond the plastic limit for an average of 36% of the days between 14 February and 9 May, compared with 68% for the 0–30 mm layer (proposed system). Wheel sinkage, bulk density and cone resistance measurements showed that a tractor would cause excessive compaction when only the surface 30 mm was drier than the plastic limit, but this could be minimized by using a low ground pressure vehicle.