SOIL PREPARATION

APPLICATION OF AMELIORANTS DURING SOIL PREPARATION The type and amount of ameliorants that should be applied during soil preparation can be determined by soil analyses. Soil preparation before planting is in fact the only opportunity to remedy low phosphorous (P) content and high acidity ( i.e . low pH) of the subsoil, as well as to apply gypsum to the subsoil. 8.1 Lime It has been estimated that 70 % of vineyards grown in the Western Cape of South Africa are grown on soils having a pH KCl < 5.0 (Conradie, 1988). Root development is seriously impeded on such acid soils (Figure 8.1) and consequently lime is applied during soil preparation to raise the pH KCl to at least 5.5 (Conradie, 1988; Oberholzer, 2016). An increase of the pH eliminates Al and Mn toxicities, and increases Ca and Mg as well as the plant availability of P and Molybdenum (Mo) in the soil. Several types of material are available to raise the pH of a soil namely: • Calcitic or agricultural lime (CaCO 3 ). • Dolomitic lime (CaCO 3 .MgCO 3 ). • Slaked lime [Ca(OH) 2 ]. • Calcium silicate slag.

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PHOTO: ARC INFRUITEC-NIETVOORBIJ.

134 | APPLICATION OF AMELIORANTS DURING SOIL PREPARATION