TECH CORNER
Sensors: It all starts with installation By Mary Love Tagert, PhD W
Below – left to right: Spatio-temporal soil moisture over an 18-hectare field on May 23, followed by a period of no rainfall until May 28 just before an irrigation application, and after an irrigation application on May 29.
hen used correctly, soil moisture sensors can be a valuable tool for helping farmers know when to irrigate. Ensuring the information
gathered by sensors is reliable and useful starts with proper installation.
Sensors should be installed in the row with the crop, and it is best to install them when the crop is young, roughly 6 inches in height. This helps to minimize damage to the crop and provides the sensors an opportunity to go through a few wetting and drying cycles while installed in the field. Installing sensors when the crop is young allows more time for the sensors to acclimate to the soil before the farmer is ready to begin irrigation applications.
It is also important to install sensors throughout the crop’s root zone. For soybeans, you might have sensors at depths of 12, 24 and 30 inches, and in corn, you might also add a sensor at a depth of 36 inches. It is critical that sensors have good contact with the soil and are “grouted” into the soil when installed.
Sensors should be placed in the best location for maximum benefit. What should you consider when determining where in the field to place sensors, and
how many sensor stations do you need per field? It can quickly become confusing when reading varying recommendations that range from one set of sensors for every 80-100 acres in a field to one sensor station for every 10-15 acres.
The short answer is that there is no set number for the density of sensors over a given area, although there is ongoing research at Mississippi State University to develop better answers to this question. The following are some general guidelines to consider.
First, consider the primary soil type(s) over your field. If you have more than one major soil type, you will want to place a set of sensors in each major soil type because soil texture affects the available water holding capacity. For example, soils with a higher clay content can hold more water. Sandier soils have a lower water holding capacity and would likely require a different, lower irrigation trigger point.
If your field slopes, it is a good idea to place one set on the higher elevation and one set on the lower end of the field. When determining sensor placement, be sure to avoid any skips in the row, and install sensors in an area of the field with representative plant emergence and spacing.
The type of irrigation application is also important when determining sensor locations. If you are irrigating using a center pivot, the recommendation is to place one set of sensors just after the start of
6 Irrigation TODAY | Fall 2019
irrigationtoday.org
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