SOIL PREPARATION

CHAPTER 6

Vine Rain or Irrigation

Root zone

Zone of moisture and salt accession Capillary fringe Water table

Saturated soil

Impermeable layer

FIGURE 6.1: Relationship between the different components of subsurface water (redrawn after Webber & Jones, 1992).

6.2 Scope and causes of waterlogging There are an estimated 1.6 million ha of land being irrigated in South Africa of which 241 630 ha are subject to high water tables and salinity, and the problems seem to be increasing (Scotney & Van der Merwe, 1995). Many viticulture areas, namely Vaalharts, Douglas, the Lower Orange River region as well as the winter rainfall regions of Robertson, Worcester, Swellendam, Ceres and Wellington, resort among the areas that experience drainage problems. This is quite understandable since subsoil drainage is a proven sustainable solution for both water-logged soils and salt accumulation in the soil (Reinders et al ., 2016). The causes of drainage problems are many, but typically are over-irrigation, leaking earthen dams and canals, blocked natural waterways, and soil layers with a slow permeability. The elimination of such causes may solve the problem or at least limit it. A soil survey, including thorough inspection of profile pits,

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