South Africa Wine Technical Yearbook 2025

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FIGURE 1: Screenshot of Netafim’s irrigation calculation tool.

What about duplex soils? When an abrupt change in texture type occurs in a soil, it is described as a duplex soil. Figure 5 is an example of a Kroonstad soil form with a clear transition between the sand in the top 30 cm and the clay from 30 cm and deeper. Clay has a very good water-holding ability, but not a lot of the water is plant-available because of the fine-textured soil particles and the way it holds water. Water also moves much slower in clay and follows an atypical distribution pattern due to the texture differences between the soil layers – Figure 6 is an illustration of this. The potential limited root depth, together with the uneven water movement, make these duplex soils difficult to irrigate. The principles

this soil needn’t be irrigated regularly. Three or four big irrigations during the summer and post-harvest period will ensure better utilisation of the water and soil resources. It is also important to take the water infiltration rate of the soil into account. In many instances, damming and surface runoff of water occur when the irrigation system delivers water faster than the soil can absorb. This can be addressed by rather using lower-delivery drippers, addressing the physical and chemical causes of the poor infiltration or establishing cover crops on the berms. There are practical examples of producers who, in such cases, will divide a big 24-hour irrigation into two 12-hour irrigations with a one or two-day waiting period in between.

FIGURE 2: Oakleaf soil

FIGURE 3: Dundee soil.

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TECHNICAL YEARBOOK 2025