Title: Variable Rate Irrigation Author
Submitted to: Judd Hill Field Day Program
Publication Type: Abstract Only
Publication Acceptance Date: August 4, 2008
Publication Date: August 28, 2008
Citation: Vories, E.D. 2008. Variable Rate Irrigation. 14th Annual Judd Hill Cotton Technology Field Day Tour Book, Trumann, Ark., Judd Hill Field Day Committee. 2008 Technical Abstract: Systems are available to producers with the ability to make variable-rate applications of defoliants, fertilizer, lime, pesticides, plant growth regulators, and seed. These systems could potentially offer a producer great cost savings; however, the full potential of these benefits and savings cannot be realized if water is not managed properly. Precision (sometimes called site-specific or variable-rate) irrigation systems allow a producer to apply different rates of water to different segments of a field. The need for variable-rate irrigation is similar to the reasons for variable-rate defoliants, fertilizer, etc. Highly variable soils within a single field (clay in lower areas with sandy loam ridges), topographic variability (high ridges, settling in fill areas after grading, or drainage ditches in a field), multiple crops and/or multiple planting dates, and overlap from adjacent pivots are a few of the situations that would be helped by variable-rate irrigation. All center pivot systems currently available from the manufacturers can apply different rates of water during irrigation by varying speed. However, these systems generally can not change the application rate along the length of the pivot. The whole system can speed up to apply less water or slow down to apply more. If a pivot is simultaneously crossing areas that are wet (drainage area) and dry (sandy), then a traditional system would have to address one problem and over- or under-irrigate the other area. Conversely, a variable-rate pivot could apply less water to the wet area and more to the dry area at the same time. The system at the Judd Hill Plantation is a true variable rate center pivot. The system was developed at the University of Georgia and installed in April of 2006 by Carl Hobbs and Jay Holder (Hobbs and Holder, LLC), with help from Shawn Lancaster of the University of Arkansas. The system was purchased by the Judd Hill Foundation and applied to an existing quarter-mile center pivot on the Judd Hill Plantation, on a portion of the Plantation farmed by Billy and Jim Baker. Cost-share funding was provided through a Conservation Innovation Grant awarded by USDA-NRCS to the University of Georgia due to the potential for water savings with variable rate irrigation. Earl Vories (USDA-Agricultural Research Service), Phil Tacker (University of Arkansas CES), and Tina Gray Teague (Arkansas State University) are leading the effort to study the utility of variable rate irrigation to the region. Larry Fowler and Shawn Lancaster of the University of Arkansas are assisting the Bakers with system maintenance. Portions of the area under the variable rate pivot are watered by adjacent pivots (a half-mile system to the north and a quarter-mile system to the east), and areas of three soil classifications (Mhoon silt loam (Mo), Dundee silt loam (DdA), and Hayti clay loam (Ha)) are under the pivot. The variable-rate system was used to irrigate cotton during the 2006 growing season to test the installation and allow the farmer and research team to become familiar with the new equipment. No significant yield differences were observed among the different application rates in 2006, probably due to rainfall at the site in July and August. Instrumentation was added to the system in 2007 to monitor its performance: a GPS unit periodically records the position of the end of the system; readings from a water flowmeter, fuel flowmeter, and a pressure sensor are stored on a datalogger and used to determine whether excessive pressure develops when portions of the system are turned off or pulsed and whether the changes to the system resulted in energy savings. Finally, a system was installed by IZON AMS to notify the producer if the water supply is interrupted or the fuel tank is low, and also allow the producer/researchers to remotely monitor the system flowrate. Additional monitoring equipment will be added as questions arise about the system performance.