Handbook for Irrigation of Wine Grapes in South Africa

Chapter 5

5.3 WATER QUALITY NORMS Most of the following water quality norms and guidelines for vineyard irrigation with respect to pH, N, P, cations, anions, trace elements and heavy metals were previously summarised and published by Howell and Myburgh (2013a & b). pH Recommended pH for irrigation water ranges from 6.5 to 8.4 (Table 5.1). Water pH can give an indication of a number of water quality related problems (ANZECC, 2000). Unsuitable water pH may cause corrosion and fouling of irrigation infrastructure. In addition, solubility and availability of plant nutrients and potentially toxic elements depend on pH (DWAF, 1996). TABLE 5.1. Effects of pH on crop yield and quality, sustainability of the soil and irrigation equipment (adapted from DWAF, 1996). pH range Crop yield and quality Sustainability Irrigation equipment < 6.5 Increasing problems with foliar damage when crop foliage is wet, Increasing problems with availability of several micro- and Increasing problems with corrosion of 5.3.1

metal and concrete in irrigation equipment. There are no problems with clogging of drip irrigation systems. Mostly no major problems with either corrosion or encrustation of irrigation equipment. Slight to moderate problems with clogging of drip irrigation systems.

could reduce yield or quality of marketable products.

macro-nutrients in toxic concentrations over the long term.

Even when crop foliage is wetted, this should not cause foliar damage in plants which will result in yield reduction or a decrease in quality of marketable products. Increasing problems with foliar damage affecting yield or reducing visual quality of marketable products.

Soil pH within this range does not present major problems with either unavailability of plant nutrients or toxic levels of elements.

6.5-8.4 (1)

> 8.4

Increasing problems with unavailability of several micro- and macro-nutrients over the long term.

Increasing problems with encrustation of irrigation pipes and clogging of drip irrigation systems.

(1) Optimum water quality range.

Most micro-nutrients and heavy metals are unavailable for uptake at high soil pH, and are only available at lower pH levels. A water pH above 8.3 may indicate the presence of HCO 3 - , CO 3 2- and Na, and the availability of trace elements may be reduced, causing nutrient imbalances (ANZECC, 2000). In contrast, acidic water may result in Al, Mn and heavy metals being mobilized in concentrations high enough to be toxic to plants (DWAF, 1996; ANZECC, 2000). Although it is not a

IRRIGATION OF WINE GRAPES 105