Subsurface Drip Irrigation
A multifactor decision for growers
For T. T. Havins of Yuma, Ariz., the decision to use subsurface drip irrigation on his 200-acre mini watermelon crop was simple. "Crops just do better on subsurface drip irrigation," Havins said. Like many other arid-land growers, Havins has used subsurface drip, furrow and center pivot over the years. Yuma, Ariz., lies on the Arizona-California border and is a major winter fruit and vegetable production area. Yuma-area growers are uniquely placed in their access to gravity-fed furrow irrigation, and their decisions to switch to subsurface drip are primarily based on quality issues for their crops.
Large-scale operations are primarily custom growers, providing their produce on contract each year, and consistent quality is essential. Not only must the produce taste good, it must also look good for display everywhere from discount chains to gourmet markets across the country. Fresh market produce is gaining popularity both locally and regionally across the country, and the quality of that produce is important to consumers.
Main canals, all gravity fed, carry water directly from the Colorado River to Yuma-area fields.
PHOTO COURTESY OF T. T. HAVINS UNLESS OTHERWISE NOTED.
Improved quality is key factor
"I have previously used drip on both cantaloupes and watermelons, but I'd been growing exclusively cantaloupes for the last 12 years, all furrow watered," Havins said. He is among a high number of growers who have had to revamp their crops after last year's food safety issue that surfaced with Colorado-grown cantaloupes, reducing market demand for the fruit.
"I had to redirect my efforts to growing these mini watermelons to continue working," Havins said. Mini watermelons have gained in popularity for their ease of handling and expanded variety development.
Havins noted that water cost is not an overriding factor in the decision to use subsurface drip irrigation systems; rather these systems are used in this area primarily to help assure a higher-quality product with improved yields.
Colorado River water is disbursed through irrigation water districts such as the Yuma Irrigation District to growers as part of an eight-state water rights compact. Because irrigation water is moved about in gravity-fed canals, growers do not have a high energy cost for extensive pumping, thus eliminating an incentive that exists in some areas. Main gravity-fed canals carry water directly from the Colorado River to the fields. Other canals, also gravity-fed and often concrete- lined, carry the water to each individual field. Water is pumped through sand media filters and onto the field. It is moved through a pressure-reducing valve into a pipe connected to the drip lines. Havins installs drip lines to each individual row, though some growers use two tapes per row. Fertilizer is injected into the water stream based on Havins' experience and on tissue sampling to determine the amount of fertilizer needed and includes all the minor elements.
Havins' watermelon rows are spaced at 84 inches. "We use a GPS-guided tractor, and the tape is injected using a homemade sled to a depth of approximately 7 inches," Havins explained. "I try to have this done well in advance of transplanting the watermelons so as to do an adequate pre-water." Although this procedure is ideal for proper irrigating of the transplanted watermelon plants, Havins noted that occasionally harvest of the previous crop does not allow the preferred time.
Aboveground lines carry water to individual fields where water moves into buried drip tape.
"With furrow irrigation, we have to stop irrigating when harvesting to allow the soil to dry. Subsurface drip allows continual irrigation to the melons that are still growing," Havins said. "While the first melons harvested may be fine, with having to stop the irrigation, the second or third harvested melons may be lower quality." With the increased emphasis on quality, maintaining that irrigation to help assure consistency is important to growers.
Early work in subsurface irrigation was done in California and Hawaii in the 1960s, with more extensive work concurrently done in Israel. Subsurface drip irrigation has generally been used in the U.S. since the mid-1980s. While irrigation of some type is essential on arid lands, such as those agricultural lands in the Southwest, irrigation has increased on non-arid lands. A number of factors must be considered in decisions to install subsurface drip irrigation.
Subsurface drip irrigation is used in spinach research trials at Texas A&M AgriLife Research and Extension Center at Uvalde, Texas, Winter Garden region.
PHOTO COURTESY OF DANA PORTER, TEXAS A&M.
Larry Schwankl, University of California Extension irrigation specialist, said, "Installing subsurface drip irrigation is a business decision with multiple factors coming into play. It's very expensive to install, generally around $1,000 or more per acre. Growers expect years out of their systems."
While irrigation is essential on arid lands, it's often supplemental in non-arid growing areas. Schwankl said, "While crops may survive in droughts on the non-arid lands, quality will be lower. When consistency is imperative, more and more growers are using irrigation, hedging their bets."
Although two motivating factors for installing subsurface drip irrigation are price and availability of water, quality of the crop being grown is increasingly a major factor in the decision to use subsurface drip. While experts emphasize that switching to subsurface drip irrigation from furrow or sprinkler irrigation is a business decision based on a number of factors, the fact that it also provides some essential elements for growing must also be taken into consideration.
Subsurface drip irrigation is a contributing factor to quality, as it allows continual irrigation during harvest for crops that are still growing.
Water savings, water availability during droughts and lower energy costs are significant issues in many areas. Crops that have varying rotations present cost challenges in drip tape installation. Drip tape, or tubing, is sometimes taken up and replaced every year, particularly on leased land. Some growers bury the tape deeper, using thicker tape, and use repeatedly. Tree and vine growers tend to use hard tubing.
Subsurface drip use is widespread
While subsurface drip irrigation is in heavy use on cotton, the primary crop on the Texas northern plains, its use on vegetables is limited. Although low-pressure center pivot has been the primary irrigation for vegetables, subsurface drip is being used on a limited basis for green chiles, squash and watermelon. Dana Porter, Texas A&M Extension engineer, is an irrigation specialist working with growers on the Texas plains. Porter said, "All of our irrigation water is groundwater." With wells ranging from depths of 200 to 400 feet in the region, there are extensive energy costs just to get the water to the surface. Low-pressure pivot avoids water loss in the irrigation process, and subsurface drip irrigation further reduces the amount of water loss.
Two annual crops are grown in the Winter Garden region near San Antonio. Daniel Lescovar is using subsurface drip irrigation extensively in vegetable research. Lescovar, research director for Texas AgriLife Research & Extension Center, Uvalde, Texas, cited the crop rotation with the two annual crops as a barrier to subsurface drip irrigation use, but noted that limited water supplies will lead to an increase in subsurface drip use. Lescovar said, "With the water situation, there's no doubt that our growers will be using subsurface drip more. Our wells have limits on the amount that can be pumped." This limit on water dictates the crops that can be grown, forcing growers to choose crops that can be grown within their water use limits.
Gravity-fed canals, sometimes concrete-lined, carry water from the main canals to individual fields.
Subsurface drip irrigation on non-arid lands
The technology is relatively new for humid climates, but with the increased interest in fresh market produce, consistent quality and appearance is expected to continue to be a major issue for growers. States such as Kentucky, which legislated specific funding for farmers who are transitioning from tobacco production to vegetable production, are using subsurface drip extensively for vegetable growing.
Craig Anderson, University of Arkansas vegetable specialist, said that about 50 percent of vegetables grown in Arkansas are on subsurface drip irrigation systems, with about 30 percent on center pivot. The remaining vegetables grown are on dry land with annual rainfall providing the needed moisture. Anderson said, "It's much easier to start with subsurface drip systems." He noted that most vegetable production is done on small acreages, and center pivots are designed for larger acreages.
Commercial vegetable production in both Kentucky and Arkansas is primarily for local and regional fresh market sales.
While a number of factors go into deciding whether to switch or initially install subsurface irrigation, subsurface has consistently produced improved yields of high quality. USDA, extension irrigation specialists, and irrigation equipment manufacturers and dealers continue to expand their understanding of subsurface irrigation for both arid and non-arid lands. Information is disseminated through publications, the Internet and hands-on workshops.
Nancy Riggs is a freelance writer. She resides in Mount Zion, Ill.