Handbook for Irrigation of Wine Grapes in South Africa

Figure 2.11

Chapter 2

1 Day

3 Days

10 Days

10

Bare soil

Mulched soil

8

a

a a a a

6

b

b

b b

b b b b bc bc c c

4 E s (mm/d)

b

b

bc

2

c c c c

c

c c c c

c

1

3

Days

0

10

1 2 3 4 5

1 2 3 4 5

Position number

FIGURE 2.11. The E s from a coarse sandy soil in the days following irrigation as measured at five positions across the work row. The mulch consisted of an 8 t/ha wheat straw layer (Myburgh, 1998).

35

T1 - Bare soil T2 - Shallow tillage

30

T3 - 4 t/ha Straw mulch T4 - 8 t/ha Straw mulch T5 - 12 t/ha Straw mulch

25

20

15

11 mm

10

5

Cumulative water loss (mm)

0

0

2

4

6

8 10 12 14 16

Time (days)

FIGURE 2.12. Effect of thickness of wheat straw mulches and tillage on water losses from the 0-20 cm soil layer in a vineyard following irrigation on 26 November 1995. Vertical bars indicate LSD (p ≤ 0.05) and arrow indicates rainfall (Myburgh, 2013). Figure 2.13 losses is by frequent, shallow tillage. The rationale behind this practice is that the layer of loose topsoil initially dries rapidly, and then acts as a mulch. However, there is some controversy regarding the use of shallow tillage to reduce E s losses. In fact, shallow tillage tended to increase evaporation losses, compared to bare, untilled soil in a vineyard near Stellenbosch (Fig. 2.12). Furthermore, it is well documented that frequent tillage will have negative effects on soil structure which may result in poor water infiltration and Another possible way to reduce E s

IRRIGATION OF WINE GRAPES 39