Handbook for Irrigation of Wine Grapes in South Africa

Chapter 4

Irrigation systems

4.1 INTRODUCTION When a grapevine absorbs water from the soil, it cannot distinguish by which irrigation system the water was supplied. The same argument applies to rainfall. Therefore, the irrigation system per se will not influence the physiological functioning of grapevines. The only exception may be where the irrigation system wets the foliage with poor quality water. This may cause damage to the foliage, or cause the uptake of toxic elements through the leaves. Globally, 95% of all irrigation is applied by surface irrigation, i.e. basin, furrow and border, whereas 4% is applied by means of drippers and 1% primarily by means of various types of sprinkler systems (http://12.000.scripts.mit.edu/mission2017/irrigation/). In South Africa, large areas of dryland (non-irrigated) vineyards were converted to irrigation the early 1980’s. Initially, overhead sprinklers were most commonly used, but in the early 1990’s the area under overhead sprinklers steadily declined (Fig. 4.1). On the other hand, the area under drip irrigation consistently increased, particularly from around 1997 until 2015. The area under micro-sprinklers also steadily increased until 2006, whereafter a steady decline occurred (Fig. 4.1). The area under flood irrigation reached a peak around 1990, followed by a steady decline. The afore- mentioned trends clearly show that drip irrigation had become by far the most popular system, compared to the other systems. In fact, most of the new wine grape vineyards are being established under drip irrigation. Although irrigation projects also consist of other important components, e.g. pumps, filters and main line networks, this chapter will focus on the components of the irrigation system used in the vineyard. It is important to note that the latter will only function properly if the design of the entire irrigation project is up to standard. In this regard, it is essential to consult with irrigation designers who are accredited to the South African Irrigation Institute. It is important that irrigation system designers use the appropriate crop coefficients for the different scenarios as discussed in Chapter 8. In many cases, the different components of irrigation systems are exposed to harsh conditions and/or aggressive water. Therefore, the quality of components used for irrigation systems is another important aspect. Ideally, all components should be tested and approved by the SABS. If equipment is only labelled “SABS tested”, it does not necessarily imply that it was approved

72 CHAPTER 4 – IRRIGATION SYSTEMS