Precision irrigation More crop per drop
Dynamic VRI uses real-time information to adjust irrigation application rates.
By Wesley Porter, PhD, and George Vellidis, PhD
“Precision agriculture” is a buzzword used frequently in the ag industry. It is a broad term that can encompass everything from using GPS devices on tractors to leveling fields with lasers. “Precision irrigation” offers a more direct focus. Although it can be defined in multiple ways, the most direct is to call it the controlled placement of water on a crop at the proper time and proper location. If we get technical with precision irrigation, it can also include the implementation of technology to better manage irrigation.
Precision irrigation can be accomplished in many ways. The more layers of data obtained about an irrigated field, the higher the level of irrigation management that can be implemented in the field. Precision irrigation for center pivot irrigation systems is often called variable rate irrigation, which is now offered by several pivot manufacturers. After-market systems are also available.
In VRI, irrigation application rates are controlled by an application or prescription map. The prescription maps are developed by dividing the fields into irrigation management zones and assigning application rates to each one. Irrigation management zones are developed by using multiple layers of data including soil texture as measured by soil electrical conductivity or estimated by soil survey maps, elevation, yield and any other relevant data that may be available to divide the field into relative uniform areas or zones.
Currently, most prescription maps are static, meaning that once they are developed and the zones are assigned application rates, those same rates are used throughout the growing season. This process can be improved by using real-time information on crop water requirements to determine and adjust the application rates of the irrigation management zones. This concept is called dynamic VRI. Dynamic VRI should result in gains in irrigation water-use efficiency or, put more simply, produce more crop per drop.
24 Irrigation TODAY | July 2018
Research at the University of Georgia has focused on work to develop and demonstrate the benefits of dynamic VRI. The approach for creating dynamic prescription maps is to use soil moisture sensors to estimate the amount of irrigation water needed to return each irrigation management zone to an ideal soil moisture condition. Systems that can populate a field with a high density of sensor nodes can be used to account for soil variability and enable dynamic prescription maps. Sensor nodes are a combination of electronics and sensors installed within a field, which measure soil moisture in terms of matric potential and wirelessly transmit the data collected. Data are uploaded hourly from these systems to web portals where they can be viewed and accessed.
A decision support tool uses the sensor data to estimate the amount of irrigation needed to bring the profile back to 75 percent of field capacity. These estimates use all the sensor nodes installed in each irrigation management zone to develop daily prescription maps that provide irrigation recommendations specific to each zone. The dynamic prescription maps can be downloaded to the VRI pivot controller remotely at daily intervals or as often as the end user prefers. When the controller receives the new prescription map, it adjusts the application rates accordingly and each zone receives the prescribed amount.
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