Handbook for Irrigation of Wine Grapes in South Africa
Sandy loam Coarse sand and Ψ m
Figure 3.1
simultaneously (Fig. 3.10). Due to the limited Ψ m range that tensiometers can measure, the in situ soil water characteristic curves are limited to ca. -70 kPa. However, computer software can be used to fit a regression model to the data. The regression model can be used to calculate the soil water content at -100 kPa, or even lower Ψ m .
10 15 20 25 30 35 40 45 50
A
30 40 50 60 70 80 90 100 110 Ȍ m (-kPa)
Figure 3.10
Soil water content (mm/30 cm)
0 5
0
10 15 20 25 30 35 40 45 50
B
y = 43 77x -0 368 R² = 0 8204
Soil water content (mm/30 cm)
0 5
0
10
20
30
40
50
60
70
80
Ȍ m
(-kPa)
FIGURE 3.10. Due to the gravelly nature of the weathered gneiss soil (A), the soil water characteristic curve (B) had to be determined in situ .
62 CHAPTER 3 – WATER RELATED SOIL PROPERTIES
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