SOIL PREPARATION

ABOVEGROUND GRAPEVINE RESPONSE

10

Several studies showed that a reduction in available soil volume decreases vegetative growth and yield of grapevines (Saayman & Van Huyssteen, 1980; Saayman & Van Huyssteen, 1982; Myburgh et al ., 1996). Uneven growth is one of the first symptoms of soil compaction that causes root restriction in vineyards (Van Huyssteen, 1989). Eventually it may even lead to dead vines in severely affected patches (Van Huyssteen, 1983). It is therefore accepted that soil preparation is necessary to obtain optimum grapevine performance. These facts immediately lead to the question as to what soil volume grapevines really require for optimum production. In practice, the question will normally be re-phrased to ask what the optimum rooting depth (instead of volume) for grapevines is. The deeper soil has to be loosened, the more costly it becomes and there also comes a stage when too great a soil volume can cause an imbalance between vegetative growth and yield as well as quality. Two long-term ground breaking field experiments at Robertson and Stellenbosch that commenced in 1967 and continued for 11 years yielded insightful results (Saayman & Van Huyssteen, 1980; Saayman & Van Huyssteen, 1982). Amongst other treatments, two depths of delving, namely 75 cm and 120 cm, as well as ripping (100 cm) were compared to a shallow ploughed (22-30 cm) control at Robertson. Vine performance, i.e. shoot growth and grape yield, was not improved by ploughing deeper than 75 cm despite the presence of a calcareous duripan or very compact subsoil that impeded root growth. This result implied that a depth of 75 cm soil was adequate for the requirement of grapevines under irrigation.

PHOTO: ARC INFRUITEC-NIETVOORBIJ.

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