SOIL PREPARATION

CHAPTER 2

FIGURE 2.2: Shallow grapevine rooting in a Tukulu soil due to natural compaction in the subsoil (Photo: ARC Infruitec-Nietvoorbij).

In addition to natural compaction, soil compaction can be caused by man- made mechanical forces of machinery wheels and tracks on the soil surface. Man-made compaction is, however, not only caused by vehicle traffic on the soil surface, but also by tillage tools operating below the surface. Depending on implement design, soil is simultaneously cut, compressed, sheared, lifted, displaced and mixed to a varying extent. Compaction, as a result of compression under tractor wheels and under implement shares and tines, occurs in vineyards as wheel tracks and traffic pans. Fortunately, because of the layout of a vineyard, tractors are always driven on the same tracks, i.e. vine rows enforce controlled traffic. Wheel compaction may already occur before planting of the vines after deep ploughing during levelling and other actions. The effect of a traffic pan on root distribution in a Wasbank soil is illustrated in Figure 2.3. Roots could not penetrate through the traffic pan to exploit the soft, loose plinthite layer underneath.

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