SOIL PREPARATION

CHAPTER 5

FIGURE 5.13: Buckling of root because growth medium behind root tip is not firm enough to support the root (Photo: W.E. Wildman, University California, Davis).

Roots that cannot grow out of the plant hole experience a potting effect. Such “potted” roots (Figure 5.14) are prone to waterlogging as well as other secondary problems due to poor aeration (Hartman & Kester, 1983) and they can of course not explore the total soil volume in search of nutrients and water. Such restricted root systems quickly dry out soil in the plant hole since they cannot exploit water in the surrounding soil. This causes water stress, especially under dryland conditions. Large root systems are important for the uptake of water and mobile nutrients such as nitrates, while an intensively- branched root system will enhance the uptake of immobile elements such as phosphate (Delver & Deckers, 1976). Grapevines with small potted root systems will therefore be prone to N shortages, but less so to P shortages. A further problem associated with waterlogging and poor aeration is a reduction of roots to take up K. Albertse & Saayman (1989) recommended that grapevines be planted in loose moist soil. Smooth walls should be loosened with a fork to facilitate root spread. Moist, loose soil can be placed in the middle of the hole in a conical heap to ensure that roots are better distributed inside the plant hole. Positioning of the vine in the plant hole can be facilitated by the use of a planting board with a notch. Vines can be placed in the notch with the graft union about 5 cm above the plank which is placed over the planting hole. After positioning a grapevine, the plant hole must be half-filled, tamped down and then filled and tamped down again. Albertse & Saayman (1989) also recommended that

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