Handbook for Irrigation of Wine Grapes in South Africa

5.3.19 OTHER ELEMENTS In addition to the elements discussed above, there are permissible levels for the elements listed in Table 5.8. However, there is no information on how grapevines and soils would respond if irrigation water contains excessive levels of these elements. Nevertheless, they should be included in water quality analyses. TABLE 5.8. Recommended maximum concentrations of trace elements and heavy metals in irrigation water as proposed by Van Zyl (1981). Element Continuous irrigation on all soils (mg/  ) Irrigation of fine textured soil for 20 years (mg/  ) Aluminium 5.00 20.00 Arsenic 0.10 2.00 Berillium 0.10 0.50 Cobalt 0.05 5.00 Lithium 2.50 2.50 Nickel 0.20 2.00 Selenium 0.02 0.02 Vanadium 0.10 1.00 IRRIGATION WITH SALINE WATER The following water quality norms and guidelines for vineyard irrigation with respect to salinity and sodicity were previously summarised and published by Myburgh (2012c). Growers are often forced to use saline water for irrigation in the viticultural regions of South Africa, notably in the semi-arid regions. If climate change reduces rainfall over the short or long term, salinity problems will increase where groundwater is not diluted. Saline irrigation water is not only detrimental to grapevine growth and yield (Fig. 5.8), but can also result in accumulation of sodium to harmful levels in soils (Moolman et al. , 1998; De Clercq et al. , 2001). Consequently, it is important to know how soils and grapevines will be affected by saline water, and how to manage such water so that its negative impacts will be minimal. The objective of this section is to provide broad guidelines for situations where vineyards are irrigated with saline water. 5.4

5.4.1

QUANTIFICATION AND CLASSIFICATION OF WATER SALINITY/SODICITY

Irrigation water is classified according to its total salt and sodium contents, as well as the effect thereof on soils and plants (Table 5.9). The salt content of water is quantified in terms of EC, whereas the SAR provides an indication of the sodium hazard (Richards, 1954). A SAR of 5 is considered to be a more realistic lower limit.

116 CHAPTER 5 – IRRIGATION WATER QUALITY