SOIL PREPARATION

CHAPTER 7

7.1 Conditions for effective implement action 7.1.1 Soil water content

Deep tillage using delve ploughs should be conducted at a soil water content at which the soil can be formed into a ball that will fall apart when slight pressure is applied by the fingers. In such a slightly moist soil, maximum break-up will be achieved. At very dry conditions, large clods are formed that cannot be exploited by roots (Figure 7.16) and, in addition, the traction required will be at its maximum. When soils are too dry for soil preparation, an irrigation of approximately 25 mm can be considered. Soil preparation can then be done two to three days later in well-drained soils such as a Tukulu or Oakleaf, which will result in a better physical soil structure than what would have been achieved in the dry soil (Vinpro, 2015). In poorly-drained soils the waiting period between irrigation and soil preparation may be longer before an ideal soil water content is reached. Tilling soils that are too wet may also cause a poor crumbling action as well as wheel slip. Soil water conditions for preparation are best when the soil surface is sufficiently dry to ensure good traction for tractors while the subsoil is still moist. The correct soil water content for soil preparation will also depend on the type of implement used. Rippers will produce better break-up of the soil at drier conditions, i.e. close to permanent wilting point. Blade delving should also be done in dry soil in order to prevent compaction of the soil due to the concentrated tractor movement.

FIGURE 7.16: Large clods that cannot be exploited by roots (left) (Photo: ARC Infruitec- Nietvoorbij) are formed when soil that was too dry is delve-ploughed and also when too wide a cutting width is used. Breaking up such large clods on the soil surface (right) (Photo: J.E. Hoffman, Stellenbosch University) by further tillage before planting will cause unintended re-compaction.

SOIL PREPARATION | 123