Georgia, like other states, has increased its irrigation capacity substantially in recent years. From about 87 center pivot systems in the 1970s, the state’s growers now are running about 10,000 pivots.
At the same time, state and federal regulatory agencies are currently developing or already have developed water-use management plans. All of this points to the urgent need for more efficient irrigation systems, and that’s where variable rate technology comes in.
Variable rate irrigation has the potential to increase crop yield and quality while saving water, says Craig Kvien, University of Georgia Extension engineer.
“During the past three years, we have field-tested variable rate irrigation systems on four commercial farms and on two experiment station sites. This system delivers water to each area within a field as needed, rather than a blanket rate or rates defined in wedges,” says Kvien.
Initial studies, he says, indicate that water-use efficiency gains of 7 percent to more than 20 percent are reasonable to expect from this system. Yields and management efficiencies also increase as a result of better water placement, he adds, and the parts for the variable rate system run approximately $5,000 for a 100-acre pivot.
“Efficient water use is critical for the development of both rural and urban communities,” says Kvien. “In the nation’s irrigation agricultural regions, agricultural water use often is estimated at 50 percent of total water consumed. New irrigation tools, when coupled with sensing systems, water management strategies and water-efficient crops, promise to improve water use efficiencies and water quality.”
Many irrigated agricultural fields have highly variable soils, he says. This variability often ranges from the very sandy to the poorly drained.
“Current pivot irrigation systems are not capable of varying the rate of water application to meet the needs of the plants on different soil types,” says Kvien. “This results in over-applying or under-applying irrigation water to the crop. In doing this, the positive economic and environmental impact of irrigation will be less than if water could be applied more precisely.”
As the result of a public and private sector partnership, a simple, cost-effective way to vary irrigation rates within a field has been developed and tested, he says. The engineering concept is to deliver water to each area within a field as needed, rather than a blanket rate or rates defined in wedges.
This system integrates GPS positioning into a control system which times (seconds on per-minute) individual or groups of nozzles off and on according to soil and crop needs in that part of the field, rather than every area getting the same rate, explains Kvien.
“In doing so, the system avoids off-target water applications such as roads, waterways and non-cropped areas, boggy spots, and overlapping pivot areas.”
The variable rate irrigation system retrofits on existing systems, he says. The major components of the system include:
-Programmable controller/software/user interface screen
-Asco air control valves (24 VDC actuated)
-Bermod flow control valves (air actuated)
-Nelson pressure control valves
-Quick-change dual flow rate spinner nozzles
-Air compressor/reservoir tanks
-DGPA receiver (for end-tower position/angle)
“In 2002 and 2003, we collected detailed information on three test pivots located in three different areas of Georgia,” he noted. “In Screven County, the 87-acre pivot saved 1,790,000 gallons of water.
“In Colquitt County, the variable rate irrigation system saved 3,560,000 gallons of water during the 2002 growing season just by controlling the end gun and the last section of the 162-acre pivot. Near Arlington, Ga., the 30-acre pivot saved 1,680,000 gallons with the variable rate system.”
The savings potential for any field is easily calculated, says Kvien. An FSA aerial image can be used to establish field size, watering zones and end gun control areas.
“Because this technology will be there year after year, the water savings will reoccur every year the system operates. Water application records - easily retrieved from the pivot controller, help to document actual water savings.
“We have documented increased yields, often due to planting and harvesting efficiencies due to each field area receiving the right amount of water, boggy areas receiving less, sandy areas receiving more, and roads and waterways receiving none.”
Cropping patterns in the field can be optimized, and growers don’t have to farm a pivot in half or quarter circles any more, says Kvien. “Also, we noted that by enabling the pivot to cover the field at optimum speed, it reduces the time needed to water a field. Variable speed control allows the pivot to move quickly over boggy spots and waterways, and it will slow down over the sandy spots, rather than running them twice. This also helps in tillage and spraying operations.”