Handbook for Irrigation of Wine Grapes in South Africa

Chapter 7

Soil water content (mass%)

0

5

10

15

0

Bare soil Shallow tillage

15

4 t/ha Straw mulch 8 t/ha Straw mulch 12 t/ha Straw mulch

30

45

Depth (cm)

60

75

90

FIGURE 7.32. Effect of shallow tillage and thickness of wheat straw mulches on soil water content on 1 December in a vineyard near Stellenbosch during the 1995/96 season (Myburgh, 2013). Horizontal bars indicate LSD (p ≤ 0.05).

It is important to note that a dry mulch will absorb rainfall or irrigation water. Consequently, the water will only reach the soil surface once the mulch becomes saturated. In the event of light rainfall or small irrigations, the water might not reach the soil at all and could evaporate into the atmosphere. This interception effect appears to increase as mulch thickness increases (Fig. 7.33). Therefore, small, frequently applied irrigations will be ineffective, and must be avoided where relatively thick mulches are applied in vineyards.

IRRIGATION OF WINE GRAPES 219