To prepare your irrigation system for winter, drain the entire above-ground systems -- filters,
valves and pumps -- after post-harvest irrigation of Walnuts, like the crews at Gold Oak
Ranch do. (Photos by Ron Goble)
A Long Winter's Nap
Cleaning, flushing saves expensive irrigation system repairs
By Ron Goble
YOLO COUNTY FARMER David Scheuring wraps up his walnut harvest around the end of October but his work is far from done. One of his first post-harvest chores, after a final irrigation, is to see that his irrigation delivery system is properly put to bed for the winter.
While most nut growers use microsprinklers in their groves, Scheuring says he has spent the last 17 years experimenting" with subsurface drip on his Gold Oak Ranch with orchards scattered between Rumsey and Davis, California. Regardless of whether you are running a drip or microsprinkler system, end-of-the season maintenance is critical, says Larry Schwankl. a University of California Cooperative Extension irrigation specialist.
Post-harvest irrigation before maintenance
If time and water supply allows. Scheuring applies a post-harvest irrigation on his walnuts. Then his crews manually open the end of every main, sub-main and lateral line and flush them. They drain the entire aboveground system-filters, valves and pumps. "A good cleaning is especially important after using the system for fertigation purposes," says Scheuring, who farms about 200 acres under one form of micro irrigation or another.
Irrigation maintenance takes place at different times, depending on the variety of nuts a grower harvests, Schwankl says. "With some almond harvests pushing well into August, post-harvest irrigations can run through September if there are no rains," he says. "System maintenance for winter should begin immediately after the final irrigation.
Gauges are an all-important warning device for your
Irrigation system. Without proper Irrigation system
maintenance, you might not realize the reason your
vines are coming under stress until itís too late.
"Generally, by the time harvest is over, nut trees require a good irrigation because they have been denied water during the harvest season and have used up what reserves were stored in the soil."
As soon as the post-harvest irrigations are over, Schwankl says growers should clean their filters and flush all the lines to rid the system of contaminants. With winter knocking at the proverbial door, there is little time to spare. Schwankl recommends flushing with plain water unless they've had system problems with bacterial slimes or lime and iron buildup.
Special attention required
While Scheuring doesn't do much in the way of special treatments, his annual attention to system cleaning helps assure a smooth transition into springtime irrigations. Scheuring reports no water quality problems at this time, although at one point he chlorinated his system to guard against root intrusion and combat a slight algae problem, which has since disappeared. A flush of root growth is common in trees after harvest, which can acerbate the root-clogging problem.
Other growers might not be so lucky.
"Some operations with a history of bacterial slime in the irrigation system should do a year-end chlorination followed by a good flushing with clean water," says the UC irrigation specialist. Sand media filters should be inspected for loss of sand and checked for bacterial growth, which would indicate the need for chlorination.
Some irrigation water has problems with chemical precipitates forming and clogging the drip system. Lime (calcium carbonate) is the most common of these precipitates. Lowering the pH by acidifying the system remedies lime precipitate clogging. Schwankl recommends a treatment of sulfuric acid at a pH of 5.5 to 6 to dissolve the lime deposits.
This can also be accomplished with a treatment of several products that are a mix of sulfuric acid and nitrogen fertilizer. The latter mixes are considered safer for handling than straight sulfuric acid, he says.
Iron woes tough to solve
Iron problems, while not widespread, are not so easily dealt with, Schwankl says. It is nearly impossible to clean up a drip system clogged with iron precipitates, but some growers have had success in preventing iron clogging by storing their irrigation water in a reservoir prior to use so the iron can oxidize into a precipitate or solid and settle out.
A relatively new treatment for excessive iron involves a continual application of phosphonic acid. There are several materials by various manufacturers that are used to keep the iron from precipitating. All of the products contain the active ingredient phosphonic acid, Schwankl says.
Subfreezing temperatures raise major concerns, particularly around irrigation valves, filters and pumping plant, Schwankl says. lf the system is not drained properly, a freeze can break valves and water meters and run up unnecessary repair bills. Growers in a historically cold area should take special note.
Reprint from: California NUTS / September-October 2002.
Contact Ron Goble at (559) 734-9046 or firstname.lastname@example.org
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