SOIL PREPARATION

2.5.3 Dorbank Dorbank (duripan in other classification systems) is reddish-brown massive to a stratified hardpan, cemented by silica (Figure 2.8) and is present in the subsoil of Garies, Oudtshoorn, Trawal and Knersvlakte soil forms. It is normally associated with environments that are more arid than areas where carbonate hardpans are found. Due to the dry areas where dorbank is formed, it can be saline and even sodic. Similar to the other hardpans, dorbank impedes root penetration and has low water permeability. Normally, by breaking up dorbank during soil preparation, a soil with a high potential for grapevines is created.

FIGURE 2.8: Dorbank, which is a serious impediment to root penetration, needs to be broken up before establishing a vineyard (Photo: ARC Infruitec-Nietvoorbij).

2.6 Waterlogging Free water can occur for shorter or longer periods at different depths in a soil profile. Sitting water tables are normally found in E horizons overlying lithocutanic, pedocutanic, prismacutanic and gley horizons. Fluctuating water tables are associated with uniformly textured soil material on concave landscapes, straight lower slopes and on flat highlands. Diagnostic soft or hard plinthic B horizons can develop at the transition between the upper boundary of the fluctuating water table and the overlying aerated soil. Waterlogging indicated by strengthening of grey colours, increases with depth below the plinthic layer. Free water can also accumulate in a variety of soil materials that

28 | SOIL IMPEDIMENTS TO ROOT PENETRATION