While California’s lingering drought highlights the need to irrigate as efficiently as possible, some growers are doing a better job of making every drop count than others.
Just ask Kevin Greer, watershed manager for the Tehama County Resource Conservation District. He’s one of a handful of Conservation District employees in the state who visit farms and ranches with a Mobile Irrigation Lab to measure how well irrigation systems are operating and, if needed, offer tips and techniques for monitoring and improving their performance.
Most of the farmers he works with grow tree nuts. One of the main problems he finds with these system is poor design. They’re not engineered to balance the ability of the pump to provide water with the ability of the lines, filters, nozzles and emitters to distribute that water in a uniform manner, Greer says
This can happen, for example, when a grower retrofits a former solid-set sprinkler system with a drip line or micro-sprinkler set up and the various components, such as length of lines, size and number of emitters, type of filters and the like, can’t handle the pressure or flow rate produced by the pump or even the quality of water being pumped.
In one recent evaluation of an impact sprinkler system in Tehama County, he found that the amount of water being applied at various locations in the orchard ranged from a high of 1.0 gallon per minute to a low of .8 gpm. (For the average pressure readings Kevin measured, the manufacturer specified flow rates of around .77gpm.)
Looking more closely, he found that wear from sand in the water had enlarged the opening in some nozzles, causing them to apply more water than needed. That .2-gallon-per-minute difference amounted to some 432 to 576 gallons over the typical 36- to 48-hour irrigation set used by the grower.
“Manufacturers design emission devices and nozzles to operate within a very specific range of pressures,” Greer says. “If they are operating outside those limits, irrigation efficiency suffers. The first thing I check is how well the system is maintaining pressure.”
Another big reason he finds irrigation systems falling short on performance is inadequate maintenance. What’s more, due to the higher number of nozzles and emitters and smaller orifices used in micro-sprinkler and drip systems, keeping them working properly is a much more labor-intensive job than a solid set system, he adds.
In some cases, filters located in the tees where the main line connects to the sub-mains can plug up. This may indicate the need for cleaning the system at other locations, such as the pump. Maybe an injection of chlorine, to control a buildup of calcium, or acid, to remove bacteria, is needed. Then, again, maybe the filtration equipment at the pump isn’t designed to remove the particular type of debris causing the problem.
To determine the type and amount of component-clogging debris in the water, Greer suggests opening the end of a line and flushing it from time to time to check for any accumulation of debris. That rate at which debris builds up will also determine the maintenance frequency.
Damage to lines from gophers, moles, rabbits and coyotes can do more than upset the balance of pressure and flow rates in micro-sprinkler and drip lines. The resulting openings can also let in silt, sand and other debris to impair performance.
Greer recommends monitoring performance of your system regularly using a flow meter at the pump and a pressure gauge at the pump before and after each filter.
“If you know your system is designed to operate at specific pressure and flow rate and then the flow changes substantially, that’s an instant red flag alerting you of a problem somewhere, such as a defective pump or a drop in the aquifer level.”