Handbook for Irrigation of Wine Grapes in South Africa

Figure 8.17

Chapter 8

A

B

PVC tube

Ex traction tube

Wetting front

Styrofoam ® rod

Plastic funnel Filter

Reservoir

Wetting front

FIGURE 8.17. Diagram illustrating (A) position of Styrofoam ® rod as water approaches wetting front detector and (B) after water had accumulated in the reservoir (Myburgh & Howell, 2015).

8.4.1.2 GRAVIMETRIC SAMPLES The gravimetric method is one of the most accurate and reliable methods used to determine soil water content. Therefore, it is often used to calibrate other methods and sensors for determining soil water content. Gravimetric soil samples are collected using a special tube auger with an inner diameter of ca. 20 mm (Fig. 8.18). A drop hammer is used to drive the auger into the soil. Soil samples are taken from predetermined depth layers. The soil samples are placed in metal cans with known mass (M c ). The lids should be replaced immediately to minimize evaporation losses. In this regard, it is also advisable to keep the samples in the shade where possible.

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