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Variable Rate Irrigation

Variable Rate Irrigation

by Bradley J. Younker, Agricultural Engineer
Natural Resources Conservation Service
Hays, Kansas

Center- pivot technology has made great advances in recent years to increase irrigation efficiencies. From monitoring center pivots using cell phones, to using moisture reading sensors in the field to determine irrigation scheduling, irrigation technology has come to the forefront in the world of precision agriculture. Another advance in center- pivot technology has been the introduction to Variable Rate Irrigation (VRI).

VRI technology works by applying water at a variable rate along the center pivot rather than one uniform rate along the entire length of the system. VRI uses Global Positioning System (GPS) and Geographic Information System (GIS) technology to prescribe a specific amount of water for certain areas of the field. This is done with the combination of GPS and GIS information sent to a “node” or control panel to run sets or “banks” of nozzles. VRI can apply no water to certain nozzles and as much as 200 percent of the normal application rate to other nozzles by opening and closing individual nozzles and speeding up or slowing down the pivot.

VRI technology has many uses for applying water at differing rates to wet areas, different soil types, and overlapping pivots, just to name a few. Another use is applying wastewater from feedyards to cropland for the nutrients in the wastewater. However, there is an issue when applying wastewater within 100 feet of the Environmental Protection Agency’s (EPA) definition of a conduit to surface water. EPA’s rule states that Confined Animal Feeding Operations (CAFOs) may not apply manure, litter, or process water closer than 100 feet to any down gradient surface waters, open tile intake structures, sinkholes, agricultural wellheads, or other conduits to surface waters. This becomes a problem when CAFO operators are trying to export wastewater to export fields and there is a “conduit to surface water” crossing the middle of the export field. Without the capability to cross the conduit with the center pivot, CAFO operators are limited to applying wastewater on smaller areas, which in turn causes export fields to become “hot” with nutrients. With VRI technology and the ability to turn sets of nozzles off, the center-pivot system would be allowed to cross the “conduit to surface water” and apply wastewater to the rest of the field and still maintain the 100 foot setback area. This in turn, increases the available land to apply wastewater on.

For more information and assistance with the planning and installation of a VRI system, please contact your local Natural Resources Conservation Service (NRCS) office or conservation district office located at your local county USDA Service Center. To learn more about NRCS, visit the Kansas NRCS Web site at

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