Handbook for Irrigation of Wine Grapes in South Africa

Chapter 3

3.11 CONCLUSIVE REMARKS Since texture is such an important soil property, it should be determined as accurately as possible when land is being surveyed for vineyard developments. This will allow growers to estimate water holding capacity, infiltration rate and saturated hydraulic conductivity. With respect to irrigation, water infiltration rate is also critical. During droughts, the limited rainfall that might occur must be able to infiltrate into the soil. Ponding and runoff will result in poor water use efficiency of this scarce resource. Furthermore, runoff may also cause soil erosion which can be disastrous to the environment in terms of soil losses. It is also expensive to reclaim land that was damaged by erosion, i.e. if at all possible. Therefore, growers must make sure the application rate of the irrigation system does not exceed the infiltration rate of the soil. Where the problem occurs in existing vineyards, growers can address the problem by incorporating organic material such as compost into the topsoil in the work rows. The positive effect of such a practice will probably last longer than mulches which tend to decay and weather rather rapidly. Cover crops in every work row instead of alternating rows will also reduce runoff losses caused by poor water infiltration. An effort should be made by research institutions to collect extensive unsaturated hydraulic conductivity data for soils in the grape growing regions. The objective must be to develop mathematic models for estimating the decline in K as the soil dries out. Preferably, the inputs should be soil properties that are easier to measure than K . Once reliable K functions are readily available, grapevine water status can be related to the water flow in the soil. To reach this objective, the research fraternity will need financial support from the industry for these basic studies. At the end of the day, the rate of water supply to the roots is the most important soil property for sustainable viticulture.

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