Research Matters - Why measure soil water tension?

As concerns grow over whether water will continue to be readily available for irrigation purposes, so it becomes ever more important to use irrigation water precisely. The review cited below is concerned with basing irrigation schedules solely on measurements of soil water tension (SWT).

Such measurements are particularly suited to areas where the soils are uniform, a definition that includes containers of standard compost mixes. Measurements of SWT then provide an accurate estimate of the force needed to extract water from the soil and can be directly related to crop yield and quality.

Of the various devices available to measure SWT, tensiometers probably provide the most direct measure and they can easily be connected to electronic data-capture systems.

The position of the sensor within the soil is critical in order to get a reliable measurement of SWT and knowledge of the soil type is also important when relating SWT to irrigation schedules. When used correctly, SWT measurements should also reduce leaching of nutrients.

The review cites the recommended SWT for various crops in various soils, including onions and potatoes. It suggests that the SWT should be between 1kPa and 6kPa for ornamental crops in greenhouses, but that it should rise to 150kPa when subjecting vines to "restricted deficit irrigation".

Soil Water Tension, a Powerful Measurement for Productivity and Stewardship by Shock and Wang (2011). HortScience 46 (2): 178-185. ISHS members can view HortScience from the website www.ishs.org


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