A tiling system that drains, irrigates too
SPENCER – With a little of maneuvering, farmers were told, they can manipulate a new concept in field tiling to either drain fields, or retain water.
Clay County Fair goers had a chance to learn on Sept. 4 the benefits of sub-irrigation from Kris Kohl, an Iowa State University agricultural and bio-systems engineer.
Kohl said sub-irrigation is a relatively new concept, with the capabilities to remove water from a field or make more ground water available to crops.
“In my work with this,” Kohl said, “we get about 80 percent of the good from getting rid of the water, and the cream on the crop is putting water back in when it’s dry.”
Kohl said when it comes to the design of the drainage water management system, tile are placed across fields on a very low slope of .001, called a tenth-grade, or less.
“A tenth-grade means that in 1,000 feet we’ll have one foot of fall on our tile,” he said. “When we put the water back in – if we raise the water on the outlet side one foot – we’re able to push the water back into the field 1,000 feet.”
Kohl said, “I’ve had some put in that are more flat (five-hundredths)-and you could put one foot of water on the lower end and push it back into your field nearly a half mile,” he said. “With the laser controls on our tile plows and tiling machines, we can get it so we don’t have any back grade and still have it at that very flat piece.”
Kohl said that where the tile enters the ditch, a pump is added to the system, either to lift water out of the ditch and get it to waiting crops, or it can pump water into the ditch.
He said producers would need an irrigation permit ($300 for 10 years) through the Iowa Department of Natural Resources.
“That gives us the right here in Iowa to put 12 inches of water on our fields,” Kohl said.
Fields are divided into zones in order to determine which way tile should be placed in order to achieve the maximum amount of carry.
Kohl said once tile is placed up and down the slopes, the ability to do sub-irrigation is lost.
Kohl said in the past, producers tend to put tile in where it can get the highest capacity out of the smallest pipe, which meant running it up and down hills and in draws.
Sub-irrigation uses the pipe to carry the water and pipes will run nearly parallel to the slope of the land so the greatest distance can be obtained for putting the water where it is needed to be.
The system involves control structures that cost between $500 and $1,000, and, Kohl said, the flatter the land, the fewer control structures are needed.
“If you have one that’s really flat down next to a river, you’re probably only going to need one $500 control structure for the whole field,” he said. “If you have flat land you can run the tile in any direction you want, but you’ll need more zones in sloping fields, so we could have (more) control structures.”
He said in that case, instead of running tiles down slopes where the highest capacity would be gained from it, tile would be parallel to the slope and controlled it at the edges of the field.
“If we run tile on sloping land at the steepest possible slope,” Kohl said, “you won’t be able to control a very big area when you’re going up (pushing water back into the field).”
DWM is part of the Iowa Nutrient Reduction Strategy, Kohl said, and there is some cost-sharing available for control structures and some of the tile.
“If we have a lot of winter drainage, it’s an opportunity to leech out some of the nitrogen that’s still there,” Kohl said. “If we bring the water table up near the surface, instead of losing the water through the profile and leeching the nitrogen out, we’ll force it to go over the top of the ground as surface flow, and we’re not going to leech our nutrients out of it,” he said.
Kohl said the outlet is raised after harvest to reduce nitrate delivery during winter. It’s lowered a few weeks before planting and harvest to allow the field to drain more fully, and the outlet is raised again after planting to potentially store water for crops.
He added that in cases he’s seen, there has been no real evidence of increased yield on shallower tile, just reductions in nutrient loss at the end of the year.
Kohl said the energy cost to subtract or add an inch of water is about 50 cents per acre.
“If you lose your drainage, you’ve lost everything,” he said.
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