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LongStop: A more Sensitive Wetting Front Detector

This pilot study evaluates the performance of the LongStop under a furrow irrigated cotton crop on a cracking grey clay soil.


  • Field test a simple device that alerts growers that drainage of water below the rootzone has reached unacceptable levels.
  • Compare versions of the Wetting Front Detector with different sensitivity limits.
  • Evaluate different fill materials for the LongStop that ensure the instrument remains in hydraulic equilibrium with the soil.
  • Provide guidelines as to how to deploy a wetting front detector on a cracking clay soil Utilise the Cotton and Grains Knowledge Project (CRD1), the CRCIF and CRC cotton extension networks for communicating the project results to irrigators.


The trial demonstrated a successful ‘proof of concept’ for WFDs under furrow irrigated cotton on cracking clay soils. The utility of the FullStop WFD is likely to lie more in the solute monitoring capability than wetting front monitoring. This is because large, infrequent irrigations are given, which penetrate well below 50 cm depth. FullStops are not ideally suited to deep placements. The value of the FullStop as an indicator of waterlogging could also be of importance to the cotton industry, as this is known to limit yields.

The LongStops performed according to theory and were able to detect weak wetting fronts at depth. They could be used to show irrigators the time period when the soil is wetter than a given suction. The variable tension lysimeter at ACRI will provide the relationship between drainage rate and suction for these soils, from which a ‘threshold’ suction can be derived. The LongStop length could then be set as a ‘switch’, to show the irrigator when they had passed this threshold suction.


The FullStop Wetting Front Detector was designed to be a simple, inexpensive and robust device that gives a yes/no response to whether a wetting front has reached a particular depth. When searching for simplicity and low cost, tradeoffs need to be made with sensitivity; in the case of FullStop the decision was made to detect a 2 kPa strength wetting front.

From a theoretical perspective, the FullStop Wetting Front Detector is not well suited to furrow irrigation, deep placement, cracking soils or where soil disturbance must be minimized. The LongStop Wetting Front Detector has been specifically designed for the above applications. Working prototypes have been built and have undergone limited field testing in sandy soils.

Publications and Resources

None listed


Land & Water Australia. 2008. LongStop: A more Sensitive Wetting Front Detector. [Online] (Updated March 9th, 2010)
Available at: [Accessed Tuesday 22nd of October 2013 09:28:24 PM ].

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id: 2327 / created: 26 June, 2008 / last updated: 09 March, 2010