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If the indicator rarely or never pops up then it is natural to wonder: "is the device still working?" We have investigated many examples, both in experiments and on-farm, where we expected the FullStop to be activated and it was not. In the vast majority of cases there was a sound explanation. It is most important that the deeper FullStop is not placed too deep. For sprinkler irrigation we do not expect the FullStop to respond frequently at 40 cm or below. For drip we do not expect the FullStop to respond frequently at 60 cm and below. The first thing to do is check that the FullStop is in working order. Use the syringe to squirt 30 ml of water into the flexible tubing. The indicator should immediately rise and engage the magnetic latch. If the float does not rise, or you suspect that the mesh filter may be blocked, please go to the section “Maintenance” on the main menu. To look at the possible reasons for non response of the FullStop click on the irrigation method you are using (sub menu).
Few or rare activations of the FullStop are most common for centre pivot and lateral move type irrigation systems. Such systems tend to apply small amounts of water at short intervals. The shallowest depth a FullStop can be placed is 150 mm (50 mm of soil above the rim of the funnel). Unless the soil is already fairly wet, irrigation amounts less than 15 mm usually do not produce a strong wetting front at 150 mm depth. Our experience with centre pivot is that detectors should be placed as shallow as possible (150 mm or 50 mm to the rim of the funnel) and even then they tend to respond more at the beginning and end of the season. We would not expect a shallow detector to respond to every irrigation during the main growing season. Small amounts of sprinkler irrigation at frequent intervals produce weak fronts that usually do not penetrate deeply into the soil. Light and frequent irrigations are generally not recommended because this increases the proportion of irrigation water that evaporates directly from the soil surface. A special case is when crops are grown on ridges or raised beds under sprinkler irrigation. We have observed that water is often shed into the furrows, either by the leaves of the crop or by water running off a crusted soil surface. In such cases it is common for a deep detector, below the depth of the furrow, to respond before a shallow FullStop in the centre of the bed. Sometimes the deep FullStop may be activated but not the shallow. This is because wetting of the soil is primarily taking place via the furrows. In such cases the FullStop should be positioned towards the edge of the beds. See under PLACEMENT for furrow irrigation In flood irrigation FullStops are generally not activated when placed in the centre of a bed. FullStops should be installed on the edge of the bed with the extension tube rising through the shoulder (link to diagram). The FullStop must be positioned where it experiences the downward movement of water from the furrow. A FullStop in the centre of a dry bed will not be activated by water that ‘wicks’ slowly across from a wet furrow. FullStops are usually activated on a regular basis under drip irrigation because the water is concentrated directly above the FullStop. When we have investigated problems in the field it has usually been one of the following
We have observed two situations where the FullStop is rarely activated under drip irrigation. The first is where wine grapes are intentionally under-irrigated to ensure quality. In such situations monitoring salt concentrations is extremely important (see Angas Bremer report under the PUBLICATIONS menu). The second is on some fine sand or silty soils that have very wide wetting patterns. When wetting patterns are wide the irrigation water does not penetrate as deep as we might expect . |
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