Handbook for Irrigation of Wine Grapes in South Africa

Chapter 5

5.5 ON-FARM WATER TREATMENT Poor water quality is one of the primary causes of clogging in irrigation systems, particularly drip and micro-sprinkler systems. Precipitates of iron and/or manganese oxides in the flow paths or the orifices can reduce flow rates substantially. High levels of Ca and/or Mg can cause the same problem. Eventually the precipitates can block water flowing though the drippers or micro-sprinklers. Once this has happened, it is almost impossible to clean the system. The best practice would be to have the irrigation water analysed on a regular basis. If the levels exceed the quality norms, acid can be injected into the irrigation system to prevent precipitation, or to dissolve oxides which had already precipitated. Acids for use in irrigation systems are hazardous chemicals. Therefore, injection systems should be designed by experts in the irrigation industry. Personnel responsible for the operation of the injection systems must be properly trained to reduce the risk of unnecessary mishaps or spills. Excessive growth, or blooms, of micro-organisms can cause irrigation system malfunctioning or clogging. When this problem occurs, chlorine gas can be injected into the irrigation system. Chlorine gas is hazardous and should also be handled, and applied, with care. Aeration of the irrigation water at the source before it is being pumped into the irrigation system will also reduce the risk of clogging. Breaking a stream of water into smaller volumes will increase the area of water exposed to the atmosphere, which will increase the formation and precipitation of oxides. If more water comes into contact with the oxygen in the atmosphere, a bigger fraction of the unwanted elements can be oxidized. Where possible, irrigation water can be aerated by cascading it over a bed of stones or rocks. Mechanical churning may also be used to aerate the water (Refer to Section 5.6.2). Due to low and irregular summer rainfall, grapevines require irrigation water for sustainable yields and quality. Unfortunately, irrigation water is a limited resource in South Africa. On the other hand, expanding urbanization and industries are increasingly producing large volumes of wastewater. Therefore, irrigating vineyards with treated wastewater could be a useful way to re-use the water, particularly winery wastewater (Howell & Myburgh, 2018). Unfortunately, the quality of most wastewaters exceeds the legislated limits presented in Table 5.11. Consequently, wastewater needs to be treated before it can be used for irrigation of agricultural crops. The purpose of this section is to discuss the viability of using treated wastewater with respect to soil conditions and grapevine responses, based on observations and research studies. 5.6 USING TREATED WASTEWATER FOR IRRIGATION

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