- Author: Ben Faber
A crucial aspect to microsprinkler and dripper performance is maintaining the size of the orifice as it was delivered from the factory. Even small changes in the size of the orifice can have significant effects on the volume of water distributed in the orchard. One of the most common causes of a decrease in orifice size or even clogging is a result of the high lime content of our waters. Calcium carbonate precipitation can readily be observed by the whitish deposits that form on emitters and microsprinklers. With the drought it's important to make that water go farther.
Reasons for carbonate precipitation include the following:
1. Change in the pH of the groundwater. This can occur when groundwater is pumped. Pumping reduces the pressure of the groundwater as it flows into the well. This reduction releases dissolved carbon dioxide gas causing the pH of the groundwater to increase. The pH increase can result in carbonate precipitation.
2. Evaporation of water in the dripper or microsprinkler. Evaporation increases the concentration of chemicals dissolved in the water remaining in the emitter. Because of its low solubility in water, calcium carbonate readily precipitates during evaporation.
3. Increase in water temperature. The solubility of calcium carbonate is reduced as water temperature increases.
4, Injection of certain chemicals, such as bleach or some fertilizers that interact with the water.
The problem of lime precipitation depends primarily on the pH of the water. At pH values less than 6, mostly dissolved carbon dioxide and a small amount of carbonic acid exist in the water. At pH values between about 6.5 and 10, bicarbonate is the dominant species. When water evaporates from the irrigation system the bicarbonate precipitates as lime if there is adequate calcium in the water. The potential for carbonate clogging is highest when bicarbonate concentration in the water exceeds 2 milliequivalents per liter (meq/L) and the pH exceeds 7.5.
This relationship of bicarbonate to water pH indicates that lowering the pH will prevent or reduce carbonate clogging of the system. Lowering the pH, dissolves any existing carbonate precipitation and prevents the formation of lime deposits.
A water's pH is lowered by injecting acids. The common acids, such as sulfuric and hydrochloric (muriatic) have been used, as well as the more expensive citric and nitric acids. An acid/fertilizer compound of a combination of urea/sulfuric acid (N-pHURIC ®) has proven to be useful and much safer than straight acids. This acidifying material is most commonly used for water treatment rather than as a source of nitrogen. If the material is used in any significant amount, its nitrogen contribution to the fertilizer program needs to be considered.
Determining frequency and amounts of acid to prevent clogging can be fairly matter of fact. Depending on the rate at which carbonate precipitation occurs, acid injection may only need to occur intermittently during the irrigation cycle to. It might only require 30-60 minutes to maintain a pH of 4. With more problematic waters, continuous acid injection to maintain a pH between 5 and 7 may be necessary.
The amount of acid needed to lower the pH to a desired level depends on the bicarbonate/carbonate concentration in the water and the target pH. The water can be sent to a lab for determining the acid amount or a trial and error approach can be used. Acid can be added to water in increments while measuring the pH until the desired pH is reached. Water pH can be measured with pH test strips or a hand held pH meter. Test kits are also readily available at swimming pool supply stores.
Other than acid for correcting lime clogging, there are several other amendments being sold on the market. Sodium hexametaphosphate has also been used and works against iron and manganese clogging. The small amount of sodium is not a problem. It is safer than an acid, but costs a bit more.
- Author: Ben Faber
Microirrigation (drip, microsprinkler, fan jet) applies water through small openings and can easily be prone to clogging. For this reason, filtration is used to avoid introducing sediments into the system and all fertilizers are injected before the filters to avoid their clogging the system. Before introducing a mixture of fertilizers into an untried system a jar test should be performed to make sure there are no chemical interactions between the irrigation water and anything that is introduced that might cause precipitation and eventual clogging. Depending on the size of emitters openings, some types are more or less prone to clogging. Anytime you use a new brand of fertilizer, make sure you do a jar test, because there have many problems in the past of just reading the label, seeing that it is soluble and then finding out to one’s horror that every emitters is clogged. For prevention of chemical and biological clogging see the article by Schwankl in this newsletter.
Microirrigation systems work best with pre-solubilized, liquid fertilizer solutions. In season application of dry fertilizers over the top of micro systems is very inefficient since only a fraction of the soil surface receives water necessary to solubilize the dry material. Very finally ground materials, such as gypsum or potassium sulfate can be suspended in solution by injectors if the materials meet the specifications of the irrigation system. The injectors continuously agitate the materials in the irrigation water to prevent settling out. The irrigation systems should be flushed after every use to prevent the materials from settling the ends of irrigation lines after the system is turned off.
Microirrigation can supply small, frequent does of nutrients throughout the growing season. Plant roots proliferate in the emitter wetted area which makes for a more active zone for taking up nutrients. Many growers have found that nitrogen fertilizer rates can be reduced due to the increased efficiency of uptake. Nutrients that require a larger root system than the microirrigation wetted pattern might need more frequent application than under sprinkler or furrow, such as potassium or micronutrients. Leaf tissue testing is a helpful too to adjust fertilizer applications, especially with a new system.
All pressurized irrigation systems require a certain amount of time to fill all laterals with water and achieve operating pressure. Injected fertilizer also requires a certain amount of time to distribute throughout the irrigation system. The ideal time to inject fertilizer is in the middle of the irrigation set. If injection takes place before the system is fully pressurized, there is a lack of uniformity if fertilizer placement (see http://cesantaclara.ucdavis.edu/files/19603.pdf). If the irrigations system is shut down before the fertilizer is fully distributed, fertilizer remains in the laterals, encouraging microbial growth that can lead to plugging. During long irrigation sets, soil mobile nutrients, such as nitrate-nitrogen should be applied near the end of the, while still allowing adequate time for system flushing.
And the mantra with all microsystems to avoid clogging is flush, flush, flush.
- Author: Larry Schwankl, Freddie Lamm, Dana Porter
Maintenance of Microirrigation Systems
Predicting Clogging Problems
Solutions to Existing Clogging Problems
System evaluation for emission device clogging
Routine Maintenance Tasks
Microirrigation systems include microsprinklers for tree crops, drip emitters for trees, vines, and some row crops, and drip tape for row and field crops. Microirrigation systems apply water to the soil through emitters that are installed along drip lines and contain very small flow passages. Microirrigation systems can apply water and fertilizers more uniformly than other irrigation methods. This uniformity results in potentially higher yields, higher revenue, and reduced irrigation operating costs.
Uniformity, a performance characteristic of irrigation systems, is a measure of the evenness of the applied water throughout the irrigation system. Distribution uniformity (DU), sometimes called emission uniformity (EU), is an index that describes how evenly or uniformly water is applied throughout the field. A uniformity of 100% means the same amount of water was applied everywhere. Unfortunately, all irrigation systems apply water at a uniformity of less than 100%, and thus some parts of a field receive more water than others. Field evaluations have shown that microirrigation systems have the potential for higher uniformity than other irrigation methods. However, clogging reduces the uniformity of applied water in microirrigation systems, thus increasing the relative differences in applied water throughout a field.
The small flow passages in the emitters and microsprinklers make microirrigation systems highly susceptible to clogging. Clogging reduces the uniformity of the applied water and decreases the amount of applied water. Clogging also decreases the amount of salt leaching around the lateral line in saline soils.
The objective of this web site is to provide information to irrigators about the causes of clogging and the methods for preventing or correcting clogging problems in microirrigation systems. Among the topics covered are the sources of clogging, chlorination, preventing chemical precipitation, filtration, flushing, and monitoring microirrigation systems.
This web site is divided into sections to allow the users to more quickly access the information they want. For example, if you already know you have a clogging problem and you want to solve it, go to the section Solutions to Existing Clogging Problems - "I have a problem and I want to solve it".