SOIL PREPARATION

CHAPTER 8

Calcitic and dolomitic lime are normally used under farming conditions. Calcitic lime is applied when the Ca:Mg ratio is < 6 while dolomitic lime should be applied at a Ca:Mg ratio > 6. In light-textured soil (less than 15 % clay) it is recommended to always use dolomitic lime. Slaked lime is more soluble than the other lime products, but is a difficult substance to handle. It forms lumps, blocks equipment such as lime spreaders and is an irritant when in contact with skin. The fineness of liming material is also very important. The finer lime is, the easier it will dissolve in the soil and neutralise soil acidity. More information on the methods of lime determination, choice of products, their neutralisation value and other information is available in Oberholzer (2016).

60

50

G1K

40

30

G1

20

Glenrosa, unlimed r = - 0.62 Glenrosa, limed r = - 0.98

10

Dry Root Mass in Subsoil (g/vine)

0

1200

1300

1400

1500

1600

1700

1800

Bulk Density (kg/m 3 )

FIGURE 8.1: Response of grapevine roots in a pot trial to an increase in soil bulk density of a limed versus an unlimed Glenrosa soil (redrawn after Conradie, 1988).

Lime moves very slowly in soil due to its poor solubility in water. Furthermore, the soil pH normally decreases, in other words it becomes more acid, with depth. Consequently effective lime application requires a method that places it deep in the subsoil and also mixes it well with the soil. Traditionally lime was broadcast on the soil surface before deep ploughing and/or cast against the slanting wall of the ploughed furrow. In a series of experiments, Saayman & Van Huyssteen (1981b) investigated the effectiveness of lime application on an Avalon soil using a locally modified sulphur duster that could blow the lime into the soil, as well as lime applied on the surface, and lime applied against the slanting furrow wall (Table 8.1). The surface applied lime was disced into

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