Testing of Low-Pressure MIcroirrigation Emitters - Horrors

The Irrigation Training & Research Center (ITRC) of Cal Poly San Luis Obispo tested 28 different pressure-compensating models of microirrigation emitting devices from a total of nine manufacturers in order to compare independent laboratory testing with manufacturer specifications.

The test results indicate that:

 

The majority of ~0.5 gallon-per-hour emitters (drippers), regardless of manufacturer exhibited:

1. Good uniformity of manufacturer

2. Had excellent response to pressure variation

3. Had consistent flow rates within the nominal operating pressure range

    

   But that the percentage of well-performing products decreased as the designed flow rate increased. Many of the emitters designated as microsprinklers or sprayers, although pressure compensating did not compensate at the normal operating pressures. Often the pressure compensating feature did not start performing until much higher pressures were achieved. Often this occurred when clogging occurred and this clogging often occurred where the pressure diaphragm was located and was not performing. Sediment would get in back of the diaphragm.  Effectively the emitters were not pressure compensating. The testing procedure of numerous medium and high flow models also found individual pieces were found to be defective. These faulty emitters had a measurable effect on the evaluation for those models.

   Read more at: http://www.itrc.org/reports/pdf/emitters.pdf

irrigATING CITRUS

Some times those microsprinklers can fool you

In order to properly irrigate any crop, you need to know how much water you are putting onto the crop. A grower with a small acreage recently asked how to irrigate avocados, and I said amongst other things that it is not only necessary to know how much water the emitters are spraying, but where that water is going. Each manufacturer rates output at a certain flow at a certain pressure. So at 20 psi a rated emitter will put out something like 8, 9, 10, 14 gpm, whatever. If pressure changes, the output changes and some emitters respond to pressure change more than others.

As elevation and distance from the inflow valve changes, pressure changes. That can be corrected by using pressure compensation in-line or at the emitter or both. So even if pressure changes, there will be a known output if the manufacturer has done right by the product. Then it is up to the grower to make sure that clogging, filter cleaning and other maintenance practices are followed.

So now the grower is left with where the water is going. When an orchard is about 8 years old in a conventional planting, the roots of all the trees are starting to get entangled amongst themselves. It becomes one big root system. So you may not think that it matters what pattern the water takes. It all gets to the trees, right? No. Because most microsprinklers as far as I know put out a pattern that puts less water in the pattern than in other parts of the pattern. Typically the water decreases with distance from the microspinkler. Lots of water near the emitter that also leaches accumulated salts from the profile, but with distance, the amount decreases and leaching decreases. The wetted pattern might look like a nice circle, but salt will accumulate with depth in that pattern because there is not sufficient water arriving at that point to drive the water below the root zone. Rain makes up for this faulty wetted pattern by leaching those accumulated salts from those underirrigated areas. A grower could compensate for lack of rain by running the system for a much longer time to make sure those poorly leached areas get a good wetting. But in a drought and with high water costs growers hesitate to put on more than they think might be necessary.

Once salt damage has occurred, though, it is not going to go away. Eventually the tree will shed those leaves and the tree will become less productive. Therefore it is important to know how much of that water is not adequately leaching the salts that are naturally occurring in the irrigation water. So our grower followed a little trial that is very commonly done in the turf trade. He put out catch cans (tuna cans with lids removed) and looked at the spray pattern of the microspinklers. He ran the system for increasing amounts of time and was able to get an idea of how much water could infiltrate at one spot.

He could then place the emitters in a pattern that might more effectively leach salts. First of all he knew that he didn't want the spray pattern to hit the tree trunks to avoid crown rot. So he could then move the emitters further away from the trunks. Also the most efficient roots for water uptake are not right at the trunk. That's where coarser roots are and much of the water will bypass them. Where the fine roots are, are further out from the trunk. So he could then move them out a little further from the trunk. At this point there comes some overlapping of the emitter spray patterns so there will be increased leaching occurring where the overlap occurs.

You can probably see where this is going. The optimum distance for a relatively mature orchard is when the emitters are midway in between trunks and there is some overlap of spray patterns. It might be necessary to on higher output emitters to make sure there is some overlap within reason. This would make the pattern of output more or less even across the wetted area. It will never be perfectly even, though, because that is not how microspinklers were designed. The grower now has a better handle on where that water was going.

 

1) Spray pattern with distance from the emitter (top graph).

2) Salt accumulation with depth and distance in that spray pattern (bottom graph).

 

 

sprinkler pattern2

sprinkler pattern1

Chemical Treatment to Prevent System Clogging

Chemical treatment of water for microirrigation systems is required when the water may cause chemical precipitate or biological clogging of the microirrigation drippers or microsprinklers. The chemical treatment varies depending on the clogging source.

Biological Clogging

Biological clogging problems are most often associated with surface waters—waters that have been stored in reservoirs or ponds, or transported in canals, rivers, etc. While it is often difficult to identify the biological contaminant, algae and biological slimes are often major contributors to biological clogging.

Groundwaters high in iron may also be a biological clogging hazard for microirrigation systems. The dissolved iron in the water provides an energy source for the iron bacteria. The gelatinous slime produced by the iron bacteria can clog emitters, often in conjunction with particulates (silt or clay particles, chemical precipitates, or other contaminants) for which they can provide a “glue” to bind particles together.

Levels of Concern

Certainly any waters that appear “green” prior to use are capable of causing biological clogging but even surface waters which appear clean may be a clogging hazard. Since surface water quality can change drastically across the season, often caused by rising temperatures and falling water levels, it is often not worthwhile to attempt to quantify the biological clogging hazard. It is better to monitor the microirrigation system for any sign of biological clogging and if it appears, treat the water. Often there is a history of biological clogging problems and the manager knows that treatment is required.

Treatment

Biological treatment methods involve using a biocide that kills the biological contaminant. The two most common biocides used with microirrigation systems are chlorine and copper. Historically, chlorine products have been most frequently injected into microirrigation systems while copper products have been used to control biological growth in ponds and reservoirs. This has changed somewhat with the availability of new copper-based formulations developed for injection into microirrigation systems.

The following are recommended levels of chlorine for biological contaminant control:

Injection Method and chlorine concentration at the end of the last lateral

Continuous injection 1-2 ppm

Periodic injection 10-20 ppm

 

Contact time between the water with chlorine and biological contaminant is important. Periodic chlorine injections should be at least 4 hours and longer is better. Chlorine injections can continue up to system shutdown, with the chlorinated water left sitting in the lines. This may have limited effect on above-ground lines since they tend to drain out at the lowest point(s), but it may help clean up other parts of the system.

Copper levels to provide effective biocide protection are also quite low, often copper levels less than 5 pm are effective. Follow manufacturer’s recommendation for formulations containing copper.

Chemical Precipitate Clogging

Most chemical precipitate clogging problems are associated with groundwater sources. Elements in solution in the groundwater may precipitate above ground and the precipitates may clog the microirrigation system’s small emitter passageways.

There are many potential chemical precipitates which can cause clogging problems, but calcium carbonate (lime) and iron are two of the more common problems. Lime precipitation is the most common and can occurwhen calcium and bicarbonate levels in the water are 2 meq/l or higher and the water pH is 7.5 or higher. 

The most common treatment for lime precipitation clogging is to lower water pH to 7.0 or below. A pH in the range of 6 to 6.5 is effective in removing the calcium carbonate precipitate while not being of risk to system components. 

Iron precipitate clogging is not as common as lime precipitation but it is more difficult to deal with. Iron precipitate clogging can occur when the iron levels are 0.2 ppm or higher, although most problems occur when iron levels are 1 ppm or higher. Water pH only needs to be 4.0 or higher for iron precipitation so this pH level includes nearly all waters.

Most people deal with iron precipitation problems by pumping the groundwater into a pond or reservoir where the iron precipitates and settles out. Adequate time is needed for the small precipitates to settle. This dictates an adequately sized pond. 

A relatively new way of dealing with iron and calcium carbonate precipitation problems is to continually inject a product containing phosphonate or phosphonic acid. The phosphonate (or phosphonic acid), injected at rates of 5 ppm or less, interferes with the precipitation. There are a number of anti-clogging formulations on the market which contain phosphonate or phosphonic acid as their active ingredient. Phosphonate or phosphonic acid products may be very beneficial for iron clogging problems, for which only aeration/precipitation and settling are currently the only solutions.

S-AV-CULT-IR[1]

Microirrigation, Fertilizers and Clogging

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.

avocado irrigation

Clogging emitters?

Maintenance of Microirrigation Systems

asphyxiation

Read more