Posts Tagged: uniformity

Irrigation Emitters - Do They Operate as Advertized?

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

   An example of the comparisons that ITRC canbee seen here of their results, compared to the manufacturers' values:

emitter performance from ITRC

Water. Water. Water. And We Still Need to Learn How to Use It Right.

A recent grower survey in Santa Barbara County asked a whole bunch of questions. One of which was had they had an evaluation of irrigation distribution uniformity. This is a free service that can significantly improve on-farm water use and most importantly improve plant health. Avocados that don't get the right amount of water at the right time are extremely susceptible to root rot. Proper irrigation is the first line of defense against root rot, good farming that results in good economic returns to the grower.

So, with a free DU available to growers, how many do you think took advantage of the service? Barely 50%!!!!!!!! This just does not make sense. In a land of little water and frequent examples of what can happen with no water ………………..and high priced water, what is going on?

The local Resource Conservation District has done many system evaluations, and most results find that improvements can be made in distribution uniformity. This is true in relatively new irrigation installations. It does not take long for problems to occur in even well designed and installed systems.

During the summer of 2007, the Casitas Municipal Water District (CMWD) contracted with the Irrigation Training and Research Center (ITRC) of California Polytechnic State University, San Luis Obispo, to conduct field evaluations of drip/micro systems. A team of two students conducted 35 field evaluations.

Distribution Uniformity (DU) – DU is a measure of the uniformity of water application to trees throughout an orchard, with DU = 1.0 being perfect. The measured orchard DUs in the Santa Barbara/Ventura area had an average DU of 0.66, while the California state average for drip/micro is 0.85.

In general, there were substantial opportunities to improve the distribution uniformity (DU) of the water to trees throughout an orchard. An improved DU will minimize over-irrigation in some areas, and reduce under-irrigation in others. Key recommendations that were provided included:

 Install a pressure regulator at the head of every hose

With a regular microsprinkler, doubling the pressure causes about 40 percent more water to come out of the nozzle. Pressure regulators are added to have similar pressures throughout the orchard and thus reduce the risk of over-irrigating portions of the field. On many farms, the difference between the highest pressures was double or even triple the lowest pressures (40-70% more water). By adding the correct high-quality, pre-set pressure regulators with the correct flow rate rating, the farmer can get similar pressures to every nozzle and prevent over-irrigation.

For a pressure regulator (PR) to work, more pressure must enter the PR than what the PR is rated for. For example, to use a 25 psi PR, you need at least 27 psi into the PR. All a PR does is reduce pressure; it cannot add pressure.

Another problem on hillsides is that some pipes have as much as 100 psi before the PR. A PR can effectively reduce the pressure down to 50%. What is recommended in these fields is to reduce the pressure in the pipe by adding an in-line valve halfway down the hill and throttling it down to a reasonable pressure.

 Completely replace all microsprinkers with pressure compensating microsprinklers

Pressure compensating microsprinklers have an internal flexible diaphragm that reduces a pathway as the pressure increases. These allow similar amounts of water to get the trees even if the hoses do not have the same pressures. Whenever the pressure is doubled, 10 percent more water will come out of these emitters, compared to 40 percent more water with a regular microsprinkler. Having pressure compensating emitters can drastically improve the DU in virtually every avocado orchard because most irrigation systems were not properly designed for microsprinkler systems, or because the farmer has altered the original design by adding different-sized nozzles.

Reduce plugging problems

Major plugging problems are found in all orchards that did not have good filtration, even those that get district water. There were also some “within-system” causes of plugging. Almost all plugging is from simple dirt or rust, as opposed to bacteria or algae. Recommendations are as follows:

• Always have a filter at the head of the system.       The required mesh size depends on the microsprinkler flow rate, but 120 mesh is a starting point.
• Remove hose screen washers that are found at the head of hoses, and replace them with regular washers (after installing a filter at the head of the system). The hose screen washers often plug up and cause the hoses to have unequal inlet pressures.
• Be sure to thoroughly flush hoses after any hose breaks.
• Double check the type of fertilizer that is being injected, especially any “organic fertilizers”. Some of these can plug emitters. In any case, inject the fertilizers upstream of the filters. If the filter plugs up, it is better to have discovered the problem early.
• Clean the filters frequently. Install pressure gauges upstream and downstream.       When the pressure differential (as compared to a clean screen) increases by 3-5 psi, it's time to clean the screen.

In some orchards, there is a big plugging problem caused by insects crawling into emitters after the water is shut off. Many of the new microsprinkler designs utilize a self-closing mechanism to prevent insects from coming into the nozzle.

We have gotten a reprieve with the rains and refilled reservoirs, but it is ever more important to make sure our irrigation systems are doing what they are supposed to be doing. Call your local Resource Conservation District and get information about a system evaluation. Contact numbers can be found at: http://www.carcd.org/rcd_directory0.aspx

irrigation pond

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

Avocados in June

No matter where they grow in California, June is a month when avocados are being watered on a regular schedule. How regular that schedule is should be carefully reviewed by the irrigator.  In 1991-'92, right along the coast in a Ventura irrigation plot, we applied 32" of water, but in '92-'93 we put on only 26".  Same trees, nearly the same size, but a 23% difference in applied amounts dictated by differences in water demand due to different weather.  The irrigation schedule we use is driven by tensiometers and a CIMIS weather station.  The station generates reference evapotranspiration values which tell us how much water to apply at an irrigation, and the tensiometers are used to verify whether the trees are doing well by the schedule.  Irrigation on a fixed schedule, such as once a week for 24 hours, is going to guarantee that on average you will be either under or over irrigating at each irrigation.  Using some soil-based measure, such as a soil probe or tensiometer can assure an irrigator that trees are getting the appropriate amount of water when they need it.  If you haven't done so, the irrigation calculator available at the Avovcadosource.com website can be quite useful in guiding an irrigation schedule - http://www.avocadosource.com/tools/IrrigationCalculator.asp - check it out.  You also need to correct for salinity accumulation.

In orchards which have not closed canopy yet, weeding is an ongoing activity. In a research plot, we are using tensiometers to monitor the effects of weeds, bare soil and chipped yard waste mulch around trees.   In weedy plots soil moisture profile rapidly show 30-40 cbars of tension at 6", whereas the bare and mulched plots can go much longer before showing 40 cbars.   Centibars is a measure of moisture tension, the higher the value, the drier the soil.  As trees get older they make their own leaf mulch and shade which limit weed growth.  There is no question that a cover crop can improve soil conditions through reduced erosion, improved water infiltration, and possible reduced disease and pest problems.   These soil improvements tend to improve tree growth and orchard productivity. But, if water is the primary issue, weeds and a cover crop can add considerably to water use in an orchard, especially a young one.  Weed control through the use of mulches and herbicides can effectively reduce the water requirements of trees.

June is still a good time to replant an orchard. The soils are warm enough to give the trees a good start and there is enough fine weather left for them to establish before winter comes.  Late plantings (September, October) are discouraged because the root-shocked plant sits in a cold, wet soil through the winter and becomes a prime candidate for root diseases.  Especially in a replant situation, it is a good idea to start them off with a fungicide with one of the phosphonate products, to give them some protection until they get established.  The best time for to apply the material to do its job on older trees is when there is a good root flush of growth which occurs after the leaf flush in spring and fall.

When replanting, try as much as possible to avoid interplanting between older trees. The different water requirements of the young and old trees is such that one or both will be stressed because they need different schedules - less but more frequent for the young trees.  Attempts can be made to put together a system where the older trees remain on the 10 or 15 gpm mircosprinkler and the young trees are put on a 1 gpm dripper.  This still cannot be an ideal situation, since the needs for application frequency are still different between the small and big trees.  The best thing to do is to clear out trees within an irrigation block and replant, or replumb a block with a new valve so that small new block can be irrigated differently from the older trees.  Where clonal rootstocks fail in a root rot replant situation, it is invariably where water control is lacking or poor.

As we all know, this has been a long dry spell in the avocado growing areas along the coast. With the levels of salt in our waters, it's important to have some kind of a leaching program to ensure that salts do not accumulate in the root zone. Each winter, rain leaches the accumulated salts from the previous irrigation season and starts the orchard off to a good start. These years it hasn't happened and one of the things that can affect the trees is a stress.  This is a salt stress that is most pronounced at the end of irrigation lines and where low pressure results in low output, often at the top of the hill.  Any irrigation system that has poor distribution uniformity is going to have areas where less water than average is applied. 

One of the responses of the trees to salt stress is to exhibit cankers in the branches. These can be silver dollar-sized cankers running in a line up the branch or as diffuse white spots in the branches.  The first symptom is related to bacterial canker and the second is to black streak.  These are not killer diseases, but they are reflective of the tree being under stress.  As soon as the irrigation schedule is corrected, these symptoms can clear up in several months.  If the schedule is not corrected the tress will begin losing leaves and sunburn can result.  The symptoms of these two problems can be viewed at the UC Integrated Pest Management website - http://www.ipm.ucdavis.edu/PMG/r8100611.html  and http://www.ipm.ucdavis.edu/PMG/r8100311.html. 

Again these are primarily stress-related diseases and the way to correct the situation is to improve irrigation distribution uniformity and the irrigation schedule. If it goes on too long it can cause problems especially in young trees. When you boil down farming to the basics, the most important activity in the orchard is ensuring proper irrigation.

 

 

avocado irrigation

To skirt or not to skirt, that is the question

There is a running debate about whether avocado canopies should be skirted up, raised up so that you can see under the canopy. In doing so, the tree’s tendency is to maintain its bearing volume by increasing a similar amount in height that is lost by removing the bottom layer of canopy. A tree with a full canopy is more cold resistant because it traps heat inside the canopy and is not so prone to cold winds. In an inversion freeze, though, warming air from irrigation, wind machines and orchard heaters is less likely to circulate when the skirts block air movement. A low skirt also impedes a uniform application of water from microsprinklers, and hence fertilizer distribution. A low skirt also has more fruit lying on the ground which is more uneven in coloration and more prone to disease and possibly food safety issues. A raised skirt also promotes more air circulation within the canopy which can reduce the incidence of some other diseases of both fruit, stems and branches.

A raised skirt, though exposes the base to light, and if there is no leaf mulch, there are more weeds to control. In the case of hillsides, because of gravity and wind exposure, leaves tend to blow away. The roots are now more exposed to drying because of increased evaporative loss. Loss of leaves is also a major disease problem, since leaves and organic matter are the first lines of defense (after proper irrigation management) against Phytophthora root rot. It is the microorganisms breaking down the leaves that create a hostile environment for the Phytophthora pathogen. In fact, in releasing enzymes to break down organic matter, the microorganisms also break down the cell walls of Phytophthora which are made of the same material as leaves. An orchard with no leaves is wide open to root rot infection.

So I propose something modest. On flat ground where trees are more prone to frost damage, and less subject to winds blowing away leaves that the trees are skirted. On slopes, though where winds blow away leaves and the trees are less subject to low lying cold, that the skirts are left. To maintain a more even water distribution, though, windows are cut into the canopy on the side facing the microsprinkler so that the canopy does not interfere with water spray.

skirting

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