Written By: Franz Niederholzer, UCCE Farm Advisor, Colusa/Sutter/Yuba Counties
Despite strong nut pricing, the drought is making 2014 a very tough year for growers, their trees, and in many cases, their irrigation systems. Low quality irrigation water, potentially stressing trees and irrigation systems, was/is applied to many orchards this year that normally received higher quality water. Irrigation system maintenance, especially cleaning drip lines to ensure uniform and adequate water flow, should be high on the do-to list this fall. The following is a quick review of key practices to keep drip emitters from clogging. For more complete information, see the sources listed at the end of the post.
In a drip irrigated orchard, keep emitters free of organic or chemical clogging by continually or periodically acidifying and/or chlorinating irrigation water. Organic clogging is more of an issue with surface water, chemical clogging is more common with ground water.
Surface water, including well water stored in a reservoir or pond, has a severe clogging potential if it carries a high organic load of algae, moss, and/or bacterial slimes. Chlorination, using chlorine gas, sodium hypochlorite (bleach), or calcium hypochlorite, can keep emitters clean either via a continual or periodic injection into irrigation water. [Super chlorination, a rescue treatment for clogged systems is risky for plants and irrigation systems and not covered here.] Inject the chlorination material upstream from the system filters, so that any precipitate can be filtered out and not be an additional plugging problem.
Hypochlorous acid is the active biocide generated when chlorine or hypochlorite is mixed with water. Hypochlorous acid activity is maximized at pH 4 to 6.5 and drops off rapidly above pH 7. So, for best results, irrigation water should be pH at 6.5 or slightly lower when chlorinating a system. Depending on the biocide source – chlorine gas or hypochlorite – you may have to acidify the irrigation water. Irrigation water is naturally acidified when chlorine gas is injected, but adding bleach to water increases pH and so an acidifier must be added, separately, to lower water pH into the range where cleaning activity is highest.
Well water with a pH above 7.5 and/or 2 meq/l bicarbonate (same as 120 ppm bicarbonate) is at risk of calcium carbonate (chalk) precipitation and chemical clogging of emitters. Injecting materials that increase irrigation water pH (aqua ammonia, bleach, etc.) or calcium containing fertilizers or amendments can also increase risk of calcium carbonate precipitation in the irrigation system. Continuous or periodic injection of acidifying materials can dissolve calcium carbonate present and prevent further precipitation. Target irrigation water pH for continuous injection is 5-7 pH, while periodic acidification target is pH 4 in the irrigation system for 30-60 minutes, minimum.
How do you know how much acid to add per minute to the irrigation water in your system? Have a lab generate a titration curve for the water from each well you use or do it yourself by trial and error in each orchard – add acid at a specific rate and then checking the pH in the system with pool test kit, litmus paper or hand-held pH meter. Then, if needed, adjust the acid injection rate and recheck pH. Repeat until the target pH is reached.
For more complete information on this key subject;
- Buy a copy of “Maintaining Microirrigation Systems” (UC ANR publication No. 21637) Order it on-line at http://anrcatalog.ucdavis.edu/Details.aspx?itemNo=21637.
- View free, on-line material from UC at: http://micromaintain.ucanr.edu/.