Handbook for Irrigation of Wine Grapes in South Africa

Chapter 7

occur. These measures are primarily aimed at reducing or preventing excessive evaporation and/or transpiration losses. Poorly managed irrigation systems may also cause unnecessary water losses. 7.2.11.1 REDUCING EVAPORATION LOSSES Soil preparation: Deep tillage before a vineyard is planted will show its benefits during critical drought periods. In most soils, grapevines will have shallow, poorly developed root systems if soil preparation is not carried out properly (Fig. 7.27A). Deep soil preparation before planting is essential for the development of deep, well- distributed root systems that can effectively absorb winter rainfall that is stored in the root zone (Fig. 7.27B). Furthermore, water absorption will be more efficient if the root system consists predominantly of fine roots. Vineyards with deep root systems will require less frequent irrigation than ones with shallow roots in the same soil, since more water can be depleted between irrigations. Consequently, the number of high Phase 1 evaporation peaks following irrigations will be less. In this way, reduced evaporation losses can save a substantial amount of water, compared to vineyards with poor root systems due to shallow soil preparation (Fig. 7.28). Figure 7.27

A

Figure 7.27

B

FIGURE 7.27. Examples of (A) a shallow, poorly developed grapevine root system, compared to (B) a deep, well developed root system with an abundance of fine roots.

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Soil water content