May 1, 2005
The term "tile" might be confusing to non-farmers who drive by a farm and see rolls of modern plastic tubing being buried in a field. Perhaps the fact that we still call this stuff tile is a testament to just how steeped in farming tradition field drainage is.
But tradition or not, new environmental concerns and economic needs are driving new technologies to the point where complex concepts like “water management” are replacing the simple term “drainage.” As it turns out, the plastic tubes that were once revolutionary have become the industry standard. Now they are allowing a new phase of water management.
In the early 1960s, extruded corrugated plastic drain tubing (CPT) replaced concrete and clay drainage tile. Cheaper and easier to use than its predecessors, CPT encouraged farmers to drain more acres. This cheaper form of “tile” has been a boon to the northern Corn Belt, where more than 30% of all cropland is drained. In Indiana and Ohio, drained acres account for more than half of active farmland.
Tile problems and solutions
As the number of tiled acres increases, so do the problems associated with drainage, such as lost water that would be a benefit during the dry season, or the valuable nitrogen and phosphorus that can be lost from soil when drainage occurs. Fortunately, because modern drainage tile is basically a plastic pipe with holes in it, there are some fairly simple and effective options for solving those problems. Drainage control structures and innovative designs for turning the drainage tubes into subirrigation systems have become economically feasible.
One example of subsurface irrigation with tile lines is found on Lazy W Farms, where Jerry Williams partners with his brother Jason to raise corn and soybeans outside of Carmi, IL. The 4,000-acre farm has 800 acres under pivot irrigation. Other fields are naturally a combination of either too wet or too dry.
The Williams brothers decided that some of their low, flat ground could benefit from better drainage during wet years. So they bought a tile plow and started installing tile lines in 2000. The brothers were generally pleased with the improved drainage from their new tile lines but wished there was a way to hold back some of that water during dry years.
In 2002, Jerry attended a presentation by Ohio State University Ag Engineering Professor Larry Brown. Brown showed farmers that it is possible to turn the tile lines on and off to retain water and that the same lines can also be used to add water as a subsurface irrigation system.
As Brown explained the requirements and advantages to creating such a system, Jerry had a test site in mind that consisted of 40 acres of flat land owned by his mother Vivian. It required both drainage and irrigation.
“After much research and personal design, Jason and I went to work with the tile plow, laying the lines on 20-ft. centers instead of the usual 50 ft. we'd normally use for drainage alone,” Jerry says. “In total, we laid about 12 miles of tile on 40 acres.”
The closer spacing was necessary to allow the tile lines to irrigate the crop efficiently. And it provided the land with super drainage. “The extra tile lines also cost us less than installing another pivot system,” Jerry says. “For irrigation, the subsurface system is also more efficient on water, reducing evaporation and eliminating dry corners in the field. Plus we're not shooting water over the road or onto the neighbor's field.”
To make the system work, the Williams's dual-duty tile lines include three water-control structures from Agri Drain Corporation. The structures are basically miniature “lock and dam” systems tied into the network of tile lines. The tile line gates can be raised or lowered at variable levels to hold back subsurface water during times of drought or let it go in the spring and during rainy periods. Though the Williams brothers control their structures manually, Agri Drain also offers a programmable solar-powered controller that can open and close the water-control gates at certain times of the year.
For irrigation via the lines, the Williams's system pumps water out of a well and stores it in a 1,500-gal. tank with a float-controlled on/off switch that Jerry and Jason designed themselves. The tile lines are charged from the tank.
Making it work
The Williams brothers did encounter some challenges with subsurface irrigation. “To avoid having water bubbling out of the ground during irrigation, you really can't have more than one foot of elevation change between one control structure to the next,” Jerry says. “We added float valves to the Agri Drain structures to help manage input of irrigation water. Also, the soil itself has to be compatible with subsurface irrigation. Clay soil like ours has a lower ability to move water laterally, which is why we spaced our tile lines closer together than normal.”
Jerry points out that it typically takes a year or two after installation for tile lines to start draining and irrigating efficiently. “Whether you are draining to tile lines or irrigating from them, the soil needs to settle,” he explains. “Water finds the path of least resistance, which on freshly disturbed soil is up and down rather than sideways. The first year after installation we planted soybeans and had a very dry September. The plants directly over the lines were much greener than those between the lines. We're guessing, and hoping, that lateral water distribution will improve as the soil settles.”
For now the Williams brothers are optimistic about the success of their controlled drainage and subsurface irrigation project, but they are taking it one step at a time. “We'll only know for sure whether this really worked or not after another season or two,” Jerry says. “But the concept makes a lot of sense, and we are seriously considering installing drainage control structures on some of our existing tile lines on other fields.”
Water table management
Ag Engineering Professor Larry Brown, whose presentation inspired the Williams brothers, confirms that installing a subirrigation system generally costs less than installing subsurface drainage and surface irrigation together.
For certain soils, subirrigation is very efficient, he says. Brown points out that, in 10 years of study, Ohio soybean yields have been consistently more than 75 bu./acre under subirrigation and a high yield management system. But it won't work in all situations, and in areas where it does work, using tile lines to irrigate still requires special management. Brown brings up the following points to consider.
Soil hydraulic conductivity, both vertical and horizontal, should be measured in the field before designing a subirrigation system. High horizontal hydraulic conductivity creates the potential for lateral seepage. This allows for a wider drain spacing. However, losses from the edge of the field may be excessive under these conditions, especially if the adjoining field is drained. Subirrigation is usually effective in soils that have a soil layer of low permeability located below the subsurface drains. This layer helps reduce deep seepage losses. The permeability of the restrictive layer should be less than one-tenth that of the crop root zone.
Gently sloping lands (less than 1% slope) are best for subirrigation because uniform depth to the water table is much easier to maintain. A field with considerable surface undulation could result in excessive variation of depth to the water table. For this case, water table management may require multiple control structures.
Monitoring the water table both over and between the drains may be necessary. Automated water level controllers reduce time inputs but are more costly. Raising the water table 4 ft. in a sandy loam soil with drains 60 ft. apart could take three to five days. Times are longer for clay soils.
Drainage system improvements may be necessary to adequately distribute the irrigation water. Drain spacing may need to be closer than required for drainage alone for certain soils. Surface improvements, such as land grading or field ditches, may be useful.
Subsurface drain spacings for subirrigation usually are 30% closer than those for drainage only. Retrofitting an existing subsurface drainage system for subirrigation may be possible in some cases by installing additional drains between existing lateral drains.
The water-control structures used on the Lazy W farm come from Agri Drain Corporation, which manufactures “smart” drainage systems designed to hold back tile drainage water and keep the water table high during winter and summer months.
Company president Charlie Schafer says this type of controlled subsurface drainage helps relieve drought stress during the growing season and reduce nutrient losses associated with drainage. The nutrient conservation aspect makes drainage control potentially eligible for government assistance funding through the Environmental Quality Incentives Program (EQIP) and possibly other conservation practices administered by the USDA. EQIP recognizes drainage water management as NRCS practice standard 554.
Products likely to qualify for EQIP funding include Agri Drain's Inline Water Level Control Structures. Prices for these structures start at around $363/unit and go up from there depending on depth of drainage needed and the diameter of the tile line.
Each structure can be controlled manually or automatically. With a cost of approximately $1,500/unit, Agri Drain's solar-powered programmable controller is designed for raising and lowering a field's water table according to seasonal needs. “This smart drainage system can be programmed to retain more water over the winter, which reduces nitrogen and phosphorus transport through the drainage system,” Schafer says. “In the spring, the system lowers the water table to allow machines to get into the field earlier for spring planting and fieldwork. In summer, the system can be set to retain more water, then release it again at harvesttime for better equipment access.”
For more information, contact Agri Drain Corp., Box 458, Adair, IA 50002, 800/232-4742, visit www.agridrain.com or www.freeproductinfo.net/fin, or circle 206. Also visit the Agricultural Drainage Management Coalition at www.admcoalition.com.
Many farmers who face wet springs say that laying more tile is the best investment they can make in their fields. Figures from the University of Minnesota are among the many that support this assumption. At an average installation cost of $0.83/ft. of tile and minimal maintenance costs, subsurface drainage is expected to increase annual net cash income approximately $60/tiled acre for soils with a potential yield of 135 bu. for corn and 40 bu. for soybeans. The expected return per tiled acre is approximately $10 greater for soils with the higher potential yields.
STOP TILE N AND P LOSS
University of Illinois Ag Engineering Professor Richard Cooke recently discussed an ongoing study that evaluates nutrient loss from tile lines. Cooke says his research shows that drainage control structures similar to those used on the Williams farm can significantly reduce nutrient loss by as much as 46% for nitrogen and 80% for phosphorus. “The water level can be raised after harvest,” Cooke says. “This reduces the flow rate from the tile, which in turn reduces the nutrient load in the tile drainage water. We aren't changing the concentrations of nutrients; we're just reducing the flow.”
Cooke also says using drainage control structures to keep the water table high after planting can help reduce the potential for drought stress, even without a subsurface irrigation component installed. “By reducing drainage after planting, we found that soil has the potential of storing about six days of water,” Cooke says. “That might not seem like much, but six fewer days of crop stress can make the difference.”
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