PUBLICATION 442-757 Filtration, Treatment, and Maintenance Considerations for Micro-Irrigation Systems Julie Shortridge, Assistant Professor and Extension Specialist, Biological Systems Engineering, Virginia Tech Brian Benham, Professor and Extension Specialist, Biological Systems Engineering, Virginia Tech Micro-irrigation systems can deliver water and nutri- Identification and Diagnosis of ents in precise amounts and at controlled frequencies directly to the plant’s root zone. With micro-irrigation Emitter Clogging systems, an extensive network of pipe is used to distrib- Clogging in micro-irrigation is often only identified ute water to emitters that discharge it in droplets, small after it becomes a problem – for instance, by noticing streams, or through mini-sprayers. The major cause of that some plants are not receiving enough water. How- failure in micro-irrigation systems is emitter plugging. ever, there are a number of actions that you can take Emitter plugging can severely degrade irrigation system to avoid clogging problems before they occur. Plug- performance and application uniformity. Because the ging hazards for micro-irrigation systems fall into three emitters are small and can easily plug, it is important to general categories: physical (sediment), biological or understand the filtration and maintenance requirements organic (bacteria and algae), and chemical (scale). Fre- of these systems and be proactive to prevent plugging. quently, plugging is caused by a combination of these The basic components of a typical micro-irrigation sys- factors. The type of emitter plugging problems will vary tem are shown in Figure 1. with the source of the irrigation water. Water sources can be grouped into two categories: surface and ground The goal of this document is to provide information on water. Each of these water sources is likely to present common water quality problems that can lead to emit- specific plugging hazards. ter clogging, and how these problems can be addressed through water treatment and system maintenance. This should help producers identify, prevent, diagnose, and address clogging problems in their micro-irrigation systems. Figure 1: Schematic of mi- croirrigation system (courtesy of Kansas State University) www.ext.vt.edu Produced by Virginia Cooperative Extension, Virginia Tech, 2018 Virginia Cooperative Extension programs and employment are open to all, regardless of age, color, disability, gender, gender identity, gender expression, national origin, political affiliation, race, religion, sexual orientation, genetic informa- tion, veteran status, or any other basis protected by law. An equal opportunity/affirmative action employer. Issued in furtherance of Cooperative Extension work, Virginia Polytechnic Institute and State University, Virginia State University, and the U.S. Department of Agriculture cooperating. Edwin J. Jones, Director, Virginia Cooperative Extension, Virginia Tech, Blacksburg; M. Ray McKinnie, Administrator, 1890 Extension Program, Virginia State University, Petersburg. VT/0218/442-757 (BSE-222P) Water Quality Analysis a water sample can be measured by how the sample The quality of the irrigation water will determine, in conducts electricity. A water quality analysis will part, the filtration, maintenance, and water treatment sometimes report electrical conductivity (EC), usually measures that are required to prevent emitter plugging in units of micromhos per centimeter (µmho/cm). To and maintain good system performance. The emit- estimate parts per million (ppm) of dissolved solids as ter characteristics, in particular the size of the emitter shown in Table 1, multiply the EC reading in µmho/cm opening, also play a part. by 0.64. For example, if the report indicates an EC of 1000 µmho/cm, then the dissolved solids concentration When analyzing water for potential use in a micro- is approximately 640 ppm. Instead of ppm, concentra- irrigation system, the analysis should include the con- tion is some times reported in mg/L (milligrams per stituents listed in Table 1. If the source is ground water liter). Note that 1 ppm equals 1 mg/L. from a relatively deep, properly constructed well (> 100 ft), the bacterial population analysis may be omitted. If The “hardness” of a particular water source is primarily the source is surface water, hydrogen sulfide will not related to concentrations of dissolved calcium (Ca) and be present and can be omitted. Table 1 provides con- magnesium (Mg), and is another indicator of its plug- centration levels for evaluating water quality in terms ging potential. If Ca and Mg are each given in ppm or of emitter plugging potential. When sampling from mg/L rather than hardness, hardness can be estimated surface water, it is important to realize that concentra- by using: tions of some constituents may change through time. Hardness = (2.5 x Ca) + (4.1 x Mg) For instance, suspended solids concentrations are likely to increase after heavy storms, and bacterial popula- where: Ca and Mg concentrations are reported in mg/L tions may be highest during hot summer months. Water or ppm. samples should be collected during times when irriga- tion would occur. If the analysis reports hardness in grains per gallon, one grain per gallon of hardness equals 17.1 ppm of hard- Table 1. Criteria for evaluating the “plugging poten- ness as CaCO3. tial” of micro-irrigation water sources. Plugging hazard based on concentration System Evaluation Factor Slight Moderate Severe In addition to testing water quality, potential clogging Physical problems can be identified and diagnosed by monitor- Suspended < 50 50 - 100 > 100 ing the amount of water being discharged from the emit- solids ters, the uniformity of this discharge, and the presence (filterable)a of contamination in system flush water. Procedures for Chemical pH < 7.0 7.0 – 7.5 > 7.5 evaluating system discharge uniformity vary based on Dissolved < 500 500 – 2,000 > 2,000 the type of micro-irrigation system. Ideally, water dis- solidsa charge is measured at multiple emitters, along with flow Manganesea < 0.1 0.1 – 1.5 > 1.5 pressure along lateral lines. Even when not all of these a Iron < 0.1 0.1 – 1.5 > 1.5 measurements are possible (for example, subsurface Hydrogen < 0.2 0.2 – 2.0 > 2.0 sulfidea irrigation system laterals cannot be accessed), system Hardnessb < 150 150 – 300 > 300 evaluations can provide information on the location and Biological severity of a clogging problem. This can be very useful Bacteria < 10,000 10,000 – > 50,000 in identifying clogging before the problem becomes so populationc 50,000 severe that it impacts crop health or becomes irrepa- amaximum measured concentration from a representative rable. Detailed steps for micro-irrigation system eval- sample (ppm), b uation are provided by the University of California hardness as ppm CaCO3, ccolony forming units per 100 ml Cooperative Extension “Maintenance of Microirriga- tion Systems” website (Schwankle, 2017). Two of the plugging hazards listed in Table 1 may be You can sometimes gain insight into the causes of a reported in units different from those shown in Table clogging problem by examining material that exits the 1. The concentration, or level, of dissolved solids in system during system flushing. To do this, flush the 2 lateral lines while holding cheesecloth or nylon mesh occur. Research has shown that using water with sus- (such as a paint straining cloth or even nylon stock- pended solids concentrations of as high as 500 ppm did ings) over the end of the line. This will catch the solid not cause emitter plugging as long as the larger par- material that is flushed out of the system while allowing ticles were filtered. If the water source contains a large the flush water to flow through. The material should be amount of silt, or is a fast-moving stream, a settling examined to see if it appears to be mostly mineral or basin may be required. In a settling basin, the velocity organic material. The color of the material should also of the water is slowed thus allowing many particles to be observed, as certain colors are associated with dif- settle out. ferent clogging causes (for instance, iron-bacteria often create orange or reddish slime). Ideally, the flush water Screen Filters should begin to appear clear after running for several minutes. If the flush water remains dirty, this could Constituents like suspended solids and sand are often indicate that particulate matter is getting through the removed using screen filters. Sizing of screen filters filter system, causing clogging. Checking filter back- is based on the maximum particle size allowable by wash water can also provide insight into contaminants the emitter, the quality of the irrigation water, the flow that may be responsible for system clogging. The soil volume between required cleanings, and the allowable around emitters can also provide clues about the source pressure drop across the filter. Information about the of clogging; white crusty material might suggest cal- maximum allowable particle size should be available cium carbonate (or lime) clogging, whereas red staining from the emitter manufacturer. If not, a conservative suggests iron precipitate may be the culprit. rule of thumb is to remove any particles larger than one- tenth the diameter of the smallest opening in the emitter. Filtering particles equivalent to one-tenth the diameter Preventing Emitter Plugging of the smallest opening and larger prevents “bridging.” Bridging is a phenomenon where small particles can join Physical plugging hazards together and plug an emitter by forming a “bridge” across the emitter opening. Table 2 shows the standard classifi- Sources of physical plugging include sand and other sus- cation of soil particulate size ranges and the correspond- pended solids that are too large to pass through emitter ing screen mesh numbers. A 200-mesh screen that has an openings. As was mentioned earlier, the characteristics opening size of 0.003 inches will remove particles the of the emitter, particularly the size of the emitter open- size of fine sand and larger and is usually adequate for ing, play a major role in the selection of the filtration micro-irrigation systems using ground water.