Handbook for Irrigation of Wine Grapes in South Africa

remain unchanged. On the other hand, it seems that near-saturation K increased in the surface layer approximately two years after a 50 cm wide compost mulch was applied on the grapevine rows (Fig. 3.19). A mini disc permeameter was used to measure K at a suction of 0.5 cm (Fig. 3.20). Visual observations revealed that the soil at the surface appeared more porous under the mulch, compared to the control without mulch. It must be noted that the 16 cm thick mulch did not increase K substantially, compared to 8 cm. Since the thicker mulch will double the cost, it will probably not be economically viable, compared to the 8 cm mulch.

300

250

200

150

100 K (mm/h)

50

y = 33.414x - 1.1518x 2 + 30.042 (R 2 = 0.9887)

0

0 2 4 6 8 10 12 14 16 18

Mulch thickness (cm)

FIGURE 3.19. The effect of compost mulch thickness on near-saturation K on the under-vine bank in a vineyard near Stellenbosch (Moffat, 2017).

A

B

FIGURE 3.20. Measuring near-saturation K by means of a mini disk permeameter (A) in the laboratory and (B) in the field.

70 CHAPTER 3 – WATER RELATED SOIL PROPERTIES