TECH CORNER
the pivot and one set at the end of the rotation just before the pivot stops. When the center pivot turn is completed, the start point will be the driest area, and this sensor station will be in the best location to determine the timing of the next irrigation application. Avoid placing sensors near the end of the pivot, as coverage is not as consistent under the end gun.
For drip irrigation systems, water application will be more precise and efficient, but it is important to remember that water needs will still vary by crop and soil type. Install sensors within the row and in the active rooting zone of the crop with roughly one sensor for every 12 inches of crop rooting depth. There are even low tension granular matrix sensors (40 centibars and below) available for greenhouse applications where rapid changes in soil water status may occur.
In furrow-irrigated fields, one set of sensors should be placed about one-third of the way down the run and another set roughly two-thirds down the run, just ahead of the tailwater. If it is not blocked, the end of the furrow is usually where water infiltration is the poorest.
There will be less soil moisture variability over the field when the soil is wetter. However, sensors installed over a field may still not read the same even after an irrigation application or a rainfall event, unless the rainfall is heavy, in which case they will all drop closer to zero. This is because water may be held in the top soil layers before reaching the deeper sensors, and crops will continue taking up water during and after an irrigation application or rainfall event. As the field starts to dry out, soil moisture variability will increase, even in a field with homogenous soils.
When using soil moisture sensors, it is important to look not only at the number the sensors are reading at a given time but also the patterns shown by soil tension readings over time. If sensors are used with these guidelines in mind and with minimal investment on your part, you will save water and money by better timing irrigation applications to match crop water needs.
Author’s note: The information provided is based on research using granular matrix soil moisture sensors.
PhD, is an associate extension professor for Mississippi State University Extension Service. The research used in this article was supported by the Mississippi Soybean Promotion Board and the Southern Sustainable Agriculture Research and Education.
irrigationtoday.org
Fall 2019 | Irrigation TODAY 7
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