A smart surface irrigation alternative
Water advances quickly during the second surge cycle at Oregon State University Malheur Experiment Station, Ontario, Ore.
“We’ve done a lot of work on ways to improve the efficiency of irrigation and reduce erosion,” says Clinton Shock, superintendent and professor of crop research, irrigation management and watershed stewardship at Oregon State University’s Malheur Experiment Station in Ontario, Ore. They’ve found that surge irrigation, which uses a computerized controller and a butterfly valve on gated pipe systems to apply water to alternate sides of a field, can increase irrigation efficiency and reduce the erosion of soil in some fields.
There are two clear indicators of when surge irrigation might be more efficient than continuous flow irrigation, Shock says: When the soil at the bottom of the field is too dry, and when growers are applying much more water than the crop needs.
With continuous flow irrigation, water tends to remain at the top of the furrow and percolate to depths that plant roots can’t use. In order to irrigate the bottom of the furrow sufficiently, growers often have to overwater. The runoff not only wastes water, it also carries soil and sediment, which contains dissolved salts and fertilizer residues that contaminate ground and surface water.
Federal and state water quality rules regarding the amount of runoff from growers’ fields are becoming more stringent, he notes.
Monty Saunders checking on a surge valve controller.
“The more runoff, the more sedimentation ponds you’ll need to keep water from exiting the fields. The more sediment from the fields, the more junk you have to take out of the ponds,” says Shock. Reducing the amount of runoff from irrigated land is better than dealing with the dirt that has to be taken out of the ponds.
Programming a surge controller.
PHOTOS COURTESY OF CLINT SHOCK.
Surge irrigation uses the same gated pipe system as continuous flow irrigation. Because the butterfly valve on the pipe-in the center of the top of the field-applies water to alternate sides of the field, the furrows partially dry between applications. As they dry, the surface soil particles consolidate and form a micro-layer that reduces the water intake rate of the soil. When water is reapplied, less is lost to deep percolation. Instead, it advances down the furrow, often more quickly than with continuous flow irrigation.
Surge irrigation uses two different cycles. The goal in the advance cycles is to irrigate until water reaches the end of the furrows but before too much begins to run off. The goal of the soak cycles is to allow water to soak into the ground. The result: More water reaches the end of the furrows, it’s distributed more evenly, and there’s less runoff.
“Surge is an advantage to growers who want to keep surface irrigation,” Shock says.
Switching from continuous flow irrigation to surge would cost much less than installing a center pivot or other sprinkler irrigation system. Existing gated pipe systems often can be converted to surge irrigation relatively easily and inexpensively. The main costs are usually the solar-powered battery controller, the butterfly valve and any additional pipe it takes to connect the existing pipes to the valve. On fields with fall in two directions, growers can place the surge valve at the corner of the field where water enters and use extra pipe to distribute the water.
Growers may save on water costs, because surge irrigation usually uses less water than continuous flow. They also can save on labor, because surge irrigation is a much more automated system, he says. They can program the controller to control both the gates and the valve.
According to the University of Nebraska- Lincoln (UNL) Extension, in general, the fields that are the most difficult to irrigate with continuous flow irrigation benefit the most from surge. Sandy and silt loam soils have the highest infiltration rates and therefore tend to have the greatest deep percolation of water, but they also form the micro-layer that reduces water infiltration when they’re alternately wet and dry.
Water cycling automatically from the right side to the left side of the surge irrigation valve and controller.
“Longer fields are really troublesome because there can be a lot of deep percolation at the upper end and not enough at the bottom,” Shock says. Surge often will distribute the water in these fields more uniformly than continuous flow irrigation does.
Slopes are also difficult to irrigate, and according to Shock, a slope of close to 1 percent or more isn’t suitable to conventional furrow irrigation or to surge irrigation.
“You’re going to be moving a lot of soil,” he says. Growers can prevent some erosion by using slower water application rates. Another factor is the crop. The ones with branches that drape into the bottom of the furrow block the water. Growers who use surge can set the timing to minimize the effect.
“Fertigation works well with surge irrigation,” Shock says. “Better than with regular furrow irrigation.”
After calibrating the injection equipment, add fertilizer to the irrigation water in front of the surge valve, preferably during the second to last cycle. The water will move the fertilizer uniformly down the furrows, and the fertilizer will remain in the upper part of the soil, minimizing the loss to deep percolation.
During the last cycle, water flushes the fertilizer out of the system, reducing the possibility that it will pit aluminum gated pipes and surge valves. Fertigation software allows growers to automatically fertilize and flush the system.
Switching to surge irrigation
The best time for growers to look into surge irrigation is when one of their fields needs to be re-leveled and the irrigation system redesigned. They should test the soil in the field by manually surging several furrows beside some furrows that are being watered with continuous flow irrigation.
“If the soil is amenable, the water will advance as fast or faster if water is applied 50 percent of the time,” Shock says.
The controllers come preprogrammed with factory settings, but growers can manually program theirs for the soil type, the length of the furrow and the amount of water available in their own fields. Although field conditions change, they’re usually fairly stable after the third or fourth irrigation, according to UNL Extension. By then, if any changes need to be made to the controller, they’ll be slight and the irrigation will be almost completely automatic.
Determining the settings involves some trial and error. Experiment by opening more gates than before, since only half of them will open at one time. The maximum flow should advance the water through the rows as quickly as possible without eroding any soil. The minimum flow should be as high or higher than before. Growers can adjust individual gates to control the flow down individual furrows.
Growers also can adjust the number and length of the cycles. After the advance cycles, the field should be wet to the end of the furrow with a minimal amount of runoff. According to UNL Extension, if the end of the furrow is still dry after the advance cycles, the soak cycles, which are shorter, may not advance water to the end.
Growers should adjust them so that enough water penetrates the soil at the end of the furrows but runoff is still minimal. Use a soil probe at both the upper and lower ends of the furrows to ensure that the water has been evenly distributed.
“I think surge irrigation is more for specialized areas,” Shock says, “but if you have a problem with furrow irrigation, try surge.”
The author is a freelance writer based in Altadena, Calif.