Drainage water: Reduce, reuse, recycle04/24/2018 | Soil Health, Water Quality
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By Carol Brown, ISA environmental communications specialist
Soda cans, fast food packaging and plastic seem to be the stars of the “Reduce, Reuse, Recycle” movement, which has been around since 1970. Today, researchers are exploring ways for farmers to reduce nitrogen in runoff, and to reuse and recycle drainage water to combat drought and have water available for crops at the right time.
Chris Hay, Iowa Soybean Association (ISA) senior environmental scientist, says that drainage water can be stored in the soil, in drainage tiles, saturated buffers and reservoirs. He is a collaborator with the multi-state “Transforming Drainage” project. He said that the project’s long-term vision is to transform agricultural drainage design and implementation to include water retention and water recycling.
Drainage water recycling is a system of storing water in a pond or reservoir and irrigating it back onto crops later in the growing season, according to Jane Frankenberger, professor of agricultural and biological engineering at Purdue University. She also is part of the Transforming Drainage project and spoke on the topic at the Iowa Soybean Association (ISA) Farmer Research Conference in February.
“Drainage water recycling benefits include increased crop yield and reduced nutrient losses coming from fields,” says Hay. “In our modeling results, Iowa crops could have benefitted from irrigation in 12 to 20 years out of 23. The average irrigation requirement — the amount of added water needed to make up rain shortfalls — ranged from 1.4 to 3.3 inches.”
Drainage water recycling could have supplied the crops with the needed few inches of water in most years. Hay evaluated available water at four research farms in Iowa and calculated crop water needs through modeling to determine these numbers.
“We need to start managing water for tomorrow’s agriculture,” said Frankenberger. “Farms have more runoff and nutrient loss in spring and more drought in summer. Both are getting worse as extreme weather increases. The solution for both is more storage of drained water in the landscape.”
Drainage water recycling isn’t new, said Frankenberger. She credited Stewart Melvin, a former professor at Iowa State University, who wrote in the 1980s of a closed loop system for recycling stored water for irrigation.
Frankenberger was upfront saying that storing water is expensive and has explored ways it can be made operational. She says to look for places where reservoirs make sense such as areas that wouldn’t require a lot of excavation or take good cropland out of production.
The next step is to figure out how much water should be stored for irrigation. She and her team at Purdue have developed a tool to calculate this.
“The Drainage Water Recycling Evaluation Tool (DWRET) provides an estimate of the average annual irrigation supply for different storage sizes — a broad outcome,” said Frankenberger. “Any type of irrigation can work with stored water: drip, overhead or sub-irrigation, by putting water back through the drainage system.”
The user, which could be a farmer, landowner or technical advisor, needs to input a few details such as the size of the irrigated field, depth of irrigation applied at one time, soil water holding capacity as well as an approximate size available for water storage. When available, the tool will be located on the Purdue University website.
Steve Killpack, a fifth-generation farmer, installed drip irrigation on his farm a year ago. Killpack grows corn, soybeans and vegetables in the Loess Hills landform region in Harrison County. He practices continuous no-till, strip cropping and uses cover crops on all his acres in addition to variable rate nitrogen application and extended rotations with a wheat crop.
Even with these conservation-minded practices in place, yield stability is a challenge with the porous loess soils, which drove him to try an irrigation system. Killpack uses a subsurface system with drip tape buried 16 inches deep, a flexible header and a filter station. The drip tape was installed along the contours of his farmland, which was the biggest issue for the installers – keeping the tape from rolling and kinking on the curves.
“My goal in the next five years is to have 500 acres of drip irrigation installed,” says Killpack. “It has the ability to give the crop what it needs when it needs it.” He runs nutrients through the drip lines in addition to the water from a nearby well.
Killpack conducted his own on-farm trial in two side-by-side corn fields. He added nitrogen and potassium through the drip lines in one field, then started irrigation on both. He said there was a 100-bushel difference between the two fields, with the lesser yields in the field that didn’t receive the nutrients.
Putting them all together
A drainage water recycling system can be set to feed above-ground sprinklers or into subsurface drip irrigation lines, which would please farmers like Killpack immensely.
Currently in Iowa there are only a handful of farms using recycled drainage water, but Hay is looking to change that.
“We have a few farmers who want to implement drainage water recycling,” says Hay. “If we have more of these systems in place, we can then study how well they work as well as the economic value they bring to a farmer’s profitability.
“Managing excess water with the drainage system, capturing water for use through irrigation in dry conditions, and having flexible nutrient application methods can be combined to provide farmers more management choices that could offset costs and maximize yield.”
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