Handbook for Irrigation of Wine Grapes in South Africa

Chapter 5

Figure 5.8

A

B

FIGURE 5.8. Examples where high levels of salinity caused typical scorched grapevine leaf edges in vineyards (A) in the Strandveld and (B) near Vanrhynsdorp.

The preferred unit for EC is deci-Siemens per meter (dS/m). Some laboratories quantify salinity in terms of electrical resistance, but R can be converted to EC as follows: EC ≈ 250 ÷ R Eq. 5.1 where 250 relates to the cell constant of a standard USDA soil cup used to measure R in Ohms. Actual amounts of salts deposited in soils via saline irrigation water can also be determined. The TDS in mg/  can be estimated from the EC of irrigation water by using the following formula: TDS ≈ 640 x EC iw Eq. 5.2 For example, if the EC iw is 0.8 dS/m, approximately 128 kg salt will be deposited per hectare if 25 mm irrigation is applied. Inputs required for salinity management primarily depend on climate, the permeability and chemical properties of soils, as well as the salt sensitivity of crops. Grapevines are considered to be moderately salt tolerant (Richards, 1954) or moderately salt sensitive (Ayers & Wescott, 1985).

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