Handbook for Irrigation of Wine Grapes in South Africa

Ca

Mg

K

Na

HCO3 SO4

Cl

Chapter 5

Figure 5.13

0 1 2 3 4 5 6 7 8 9

Philadelphia

Malmesbury

Level in water

pH

EC

SAR

Fe

B

Mn

FIGURE 5.13. The pH, EC in dS/m and SAR, as well as Fe, B and Mn concentrations in mg/  in treated municipal wastewater used for irrigation of vineyards near Philadelphia and Malmesbury, respectively.

0 2 4 6 8 The soil chemical status at budbreak was also monitored over ten years in three drip irrigated vineyards near Philadelphia. Soil analyses showed that the ESP varied considerably over time, and reached excessively high levels in the subsoil (Fig. 5.14). This is an alarming trend, since the water SAR was on average less than 10, i.e. within the quality norms for wastewater irrigation (Table 5.11). However, results indicated that the accumulation of Na in the soil profile depended on the winter rainfall, i.e. between May and September (Fig. 5.14B). In general, this implies that some of the salts will accumulate if the winter rainfall is low, and some will be leached into deeper layers following high winter rainfall. It must be noted that the nature of the rainfall could affect the amount of salts that will be leached. Although the total rainfall could be high, it could consist of numerous small showers. Therefore, less salts will be leached, compared to a few heavy downpours adding up to the same total. This probably explains the outlier value indicated in Figure 5.14B. A Figure 5.14

0-30 cm 30-60 cm 60-90 cm

50 100 150

-8 -6 -4 -2

Change in ESP (%)

Y = -0.0802 + 13.87 (R 2 = 0.92

Rainfall (m

07 08 09 10 11 12 13 14 15 16

IRRIGATION OF WINE GRAPES 125