1986 - Volume #10, Issue #4, Page #35[ Sample Stories From This Issue | List of All Stories In This Issue | Print this story | Read this issue]
Below-Ground 2-Pipe Irrigation System
Ken Thornton, a drainage tile contractor in Polk City, says using drainage tile alone to irrigate is inefficient and may even cause damage to fields and crops. He recently installed his first 2-pipe underground irrigation system at the Iowa State Research Farm near Ankenny.
The idea is to pump water, nitrogen, fertilizers, herbicides and even oxygen to the crop through a 3-in. dia. perforated pipe, buried about 22 in. below the surface, and carry away the run-off through drainage tile buried 4 ft. or more below the surface.
"It lets us pump water and nutrients to the crop at any time. If your corn needs water and nitrogen in the middle of July, you simply feed it in through the system," says Thornton.
Other new sub-surface irrigation systems pump water into the crop by forcing water back up the drainage tile, in effect flooding the field from underground. Thornton doesn't like the idea.
"You have to raise the entire water table to get water to the crop from deep tile and the constant ebb and flow of water can cause silt to build up in tile. Also, when you flood the field you tend to eliminate oxygen from the ground which plants need to grow. In addition, if you get heavy rains it can take as long as 12 days to change from irrigation back to drainage if the ground is already flooded," says Thornton.
If your fields are already tiled, you can install Thornton's system by installing the feeder-pipe above it at about 90% of the spacing of the drainage tile. When buried at about 22 in. ù depending on soil type ù Thornton says it'll spread out over a 100-ft. area or more, working it's way out horizontally from the pipe. Water and nutrients that are not needed drain out the tile and are carried back to a central location. Because the pipe is buried just 22 in. deep, the system requires a switch to no-till, eliminating deep-till equipment.
"We're actually able to increase soil tilth with this system by pumping compressed air into the ground through the pipe when we're not pumping water and nutrients. The oxygen stimulates bacteria which break down organic matter in the soil faster," says Thornton.
He notes that the system may cost as much as $1,000 per acre to install from scratch. But, if you already have drainage tile installed, the cost would be around $350 to $400. "It must be engineered to your soil structure and type. Depth of the irrigation pipe is critical, and can vary from 13 in. to 3 ft."
The system installed at Iowa State pulls water from a pond with a 1 hp. motor, adding chemicals on the go. Water that drains down to the drainage tile is pulled out with a ¢-hp pump and then filtered before being dumped back into the supply pond.
Thornton is working with Robert Horton, associate professor of agronomy at Iowa State and researchers from Pioneer Hi-Bred International, Inc., who provided seed corn on the experimental plot.
For more information, contact: FARM SHOW Followup, Ken Thornton, Water Management Technologies, 215 E. Grimes St., Polk City, Iowa 50226 (ph 515 984-6678).
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