Drip Irrigation Scheduling
Causes And Prevention Of Emitter Clogging In Microirrigation Systems
For Your Information Irrigation System Evaluation
A Guide On Soil And Water Management For Local Officials
Drip Irrigation Of Row Crops: An Overview
Equation to convert depth of water to volume
V = (C1)(D)
V = volume of evaporative demand
C1 = conversion factor
D = depth of water
Conversion factors relating depth of application to volume
Units of D Row Length of row/ Value of Units of V
spacing unit area C1
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feet feet/acre 27,152 gal/acre
inches 3 14,520 187 gal/100ft
4 10,890 249 gal/100ft
5 8,712 312 gal/100ft
6 7,260 374 gal/100ft
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Example. A drip-irrigated tomato crop planted on raised beds spaced on six-foot centers with an evaporative demand of 0.15 inch/day would require a volume (V) of water equivalent to:
374 (gal/100ft. per inch) X 0.15 (inch/day) = 56 gal/100ft/day
Therefore, if the field had 15,000 ft. of row,
150 X 56, or 8,400 gal/day of water would be required.
Drip systems average 80% to 90% in water application efficiency, with the actual efficiency dependent on system design, operation and cultural arrangement. Therefore, additional water is required to compensate for the loss in efficiency.
Example: If water were applied daily in the above example at 90% efficiency, then
8,400 gal/day divided by 0.90 = 9,333 gal/day needed.
Equation for basic water budget
CS = PS + ER + I - ETc
CS = current storage
PS = previous storage
ER = effective rainfall
I = irrigation
ETc = crop evapotranspiration
Two equations to convert emitter discharge
Q1 = (C2)(Qe)/Se
Qt = (C3)(Qe)(L)/Se
Q1 = lateral water discharge per unit length
Qt = gross water discharge per unit area
C2 = conversion constant
C3 = conversion constant
Qe = emitter discharge
L = length of drip tube per irrigation area
Se = emitter spacing
Use appropriate values of C2 and C3 for different unit combinations of Qe, L, and Se.
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Values of conversion constants to convert emitter discharge to unit length or unit area
______________________________________________________
Units Units Units Value Value Units Units
of Qe of Se of L of C2 of C3 of Q1 of Qt
_______________________________________________________
gph inches ft/acre 1,200 12 gph/100' gph/ac
inches ft/acre 20 0.2 gpm/100' gpm/ac
feet ft/acre 100 1 gph/100' gph/ac
feet ft/acre 1.67 0.017 gpm/100' gpm/ac
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Example. A drip tube with an emitter discharge rate of 0.3 gph, an emitter spacing of 9 inches, and a total length of 7,260 feet of tube per acre would have a corresponding Q1 of:
20 (gpm/gph)(inch/100 ft) X 0.3 gph divided by 9 inches = 0.67 gpm/100ft
and a Qt of:
0.2 (gpm/gph)(inch/ft) X 0.3 gph X 7,260 (ft/acre) divided by 9 inches = 48.4 gpm/acre
In order to determine the effective application rate, either Q1 or Qt is divided by the fractional equivalent of application efficiency. Required times can then be determined by multiplying the modified Q1 or Qt values by the total length of tube per irrigated zone (expressed as 100 ft lengths) or by the production area per irrigated zone in acre, respectively.
Irrigation Journal, PO Box 2180, Cathedral City, CA 92235-2180.
CAUSES AND PREVENTION OF EMITTER CLOGGING IN MICROIRRIGATION SYSTEMS
Microirrigation systems can conserve water and improve crop growth and yields by delivering precisely controlled water and nutrient application to plants. Both water and nutrients are typically delivered at low flow rates in small, frequent applications as required for optimum plant growth.
Emitters with small orifices are used to deliver the required low flow rates, and these small orifices can readily be clogged by poor water quality if the microirrigation system is not properly designed and managed. Clogged or partially clogged emitters will reduce the uniformity of water and nutrient applications, thus reducing the uniformity of plant growth and reducing yield.
The success of microirrigation depends directly on the ability of the system manager to prevent emitter clogging. This article discusses causes and prevention of emitter clogging in microirrigation systems.
Causes of Emitter Clogging
Emitter clogging is caused by particulate matter, biological growths, chemical precipitates or combinations of these factors that block emitter orifices. Irrigation water may cause clogging; however, poor system design and management can also cause or contribute to clogging.
Particulate Matter: Emitters can be particles of sand, limestone or other debris that are too large to pass through small passageways. Clogging can also occur if small particles join to form larger obstacles. Even very small particles such as suspended clay, which would not cause problems as individual particles, can cause clogging if they flocculate to form larger particles.
Biological Growths: Emitters can be clogged by large particles of organic materials that directly block emitters if they are not filtered. They can also be clogged by microscopic organisms such as algae and some bacteria whose byproducts lead to clogging. Large organisms such as weeds are fish are often found in ponds and other surface water sources. Many types of algae are small enough to pass through filters and emitter passageways as individual particles, but may flocculate in pipelines to form particles large enough to clog emitters. Bacteria are small enough that their size does not cause clogging; however, they can precipitate iron, sulfur and other elements to clog emitters. Some bacteria secrete slime that act as adhesive surfaces for the accumulation of clay, algae and other small particles.
In Florida, iron and sulfur bacterial growths are common problems. Iron precipitation bacteria grow in the presence of dissolved ferrous iron in irrigation water. These bacteria attach to surfaces and oxidize the dissolved iron, precipitation it as insoluble ferric iron. In this process, the bacteria create a slime called ochre that can combine with other materials in pipelines and clog emitters.
Sulfur slime is produced by certain bacteria that can oxidize hydrogen sulfide and produce insoluble elemental sulfur. Sulfur slime is a white or yellow stringy deposit formed by the oxidation of hydrogen sulfide present in many shallow wells in Florida. This slime can clog emitters either directly or by acting as an adhesive surface for other small particles.
Chemical Precipitates: Chemical clogging of emitters usually results from one or more of the following minerals: calcium, iron, magnesium and manganese. These minerals can precipitate from solution and form scale that may partially or fully clog emitters. Precipitation can be caused by changes in pH, temperature, pressure, other irons in solution such as fertilizers injected in irrigation water and exposure to oxygen in air.
Iron is another source of precipitate that can clog emitters. Iron is often dissolved in groundwater as ferrous bicarbonate. When exposed to air, the iron oxidizes and precipitates. Manganese is sometimes also present, but in lower concentrations.
Fertilizer Injection: Fertilizer elements injected into a microirrigation system (fertigation) may contribute to emitter clogging. Fertilizer elements differ widely in their solubility, which is dependent on the irrigation water quality, pH and temperature. Thus, it is difficult to predict whether a specific combination of fertilizer elements will cause clogging problems for a given application. In general, highly soluble fertilizer formulations will lead to fewer clogging problems, while poorly soluble or suspended materials will cause more problems.
Because of the potential for clogging by fertigation, the following solubility test should be conducted:
1. Add drops of the liquid fertilizer to a sample of the irrigation water until the concentration is equal to the fertilizer concentration planned for the irrigation system;
2. Cover and set the mixture in a dark place for at least 12 hours so that any chemical reactions can occur; and
3. Shine a light into the bottom of the container to see if precipitates have formed. If no precipitates have formed, the fertilizer source will normally be safe to use in that specific irrigation water source.
Preventing Emitter Clogging
A properly designed microirrigation system must include provisions to prevent emitter clogging. These provisions may include a water quality analysis to identify the severity of the clogging problem anticipated, a filtration system and aeration/settling ponds. A system for flushing water may be the source of clogging problems. However, poor system design and management can also cause or contribute to clogging. Thus, proper microirrigation system design requires proper selection of emitters and other components and a system management plan to prevent clogging.
Water Quality Analysis: A water quality analysis will help to identify potential clogging problems due to water quality. Preventive measures can then be anticipated. Water quality analyses specifically designed for microirrigation should be requested.
Filtration Systems: Many types of microirrigation filters are commercially available. Filters should be selected based on the minimum particle size to be removed and with sufficient capacity for the largest, anticipated system flow rate. Emitter manufacturers often specify the filter size required, or in the absence of manufacturer's recommendations, to remove all particles larger than 1/6 to 1/10 of the minimum diameter of the emitter flow path.
If the material to be filtered is inorganic particulate matter such as sand or flakes of limestone, screen or wafer (disk) filters should be adequate. This is often the case for well water. If large quantities of sand or other dense particles are being pumped, they can be removed by using vortex (centrifugal) filters followed by screens. Settling basins can be used to remove large quantities of sand if the basin is also required for aeration to precipitate iron or other minerals. However, settling basins may introduce organic debris into the irrigation water; thus, they should be avoided if possible. If the water to be filtered includes substantial amounts of organic debris, screen filters will clog quickly. In that case media filters, followed by screen filters, are required. For only small amounts of organic debris, wafer filters are often adequate because they provide more filter-surface area than screens of the same size.
Pump intakes should be equipped with strainers to prevent large debris from entering the pump. Also, surface water intakes should be located below the watersurface to avoid floating debris, but above the bottom to avoid sediment.
Flushing System: Small particles of both organic (such as algae) and inorganic (such as clay or silt) materials will pass through filters and into microirrigation systems. These particles can settle and accumulate in pipelines and emitters, eventually leading to clogging problems. To minimize sediment buildup, regular flushing of microirrigation pipelines is required. Valves should be installed for flushing of mainlines, manifolds and laterals. Flushing should be done as needed based on water quality and the amount of material found in pipelines. If considerable sediment buildup occurs, laterals might be equipped with automatic flush valves that flush at the start of each irrigation.
To reduce the potential for emitter clogging when fertilizer is injected into microirrigation systems, flush all fertilizer from the system each time fertilizer is injected if possible. For shallow-rooted crops such as vegetables grown on low water-holding soils, the required short irrigation durations might prohibit flushing the system without leaching below the crop rootzone.
Chemical water Treatment: Chemical water treatment is often required to prevent emitter clogging because of organic growths and mineral precipitation. Chlorination is effective against both organic growths and chemical precipitates. Acid injection can dissolve scales, prevent precipitation and create an environment unsuitable for organic growths. Scale inhibitors can prevent the buildup of scales that might cause clogging problems. Most irrigation textbooks that discuss microirrigation examine the chemistry of water treatment in depth.
Chlorination: Chlorination is the most common method used to treat many microirrigation clogging problems. Chlorination will kill bacteria and other organic growths in pipelines. Since bacteria can grow within filters, and since chlorination may cause certain precipitates to form, chlorine always should be injected before the filter.
Liquid sodium hypochlorite (NaOC1), the same formulation as laundry bleach, is effective and easy to handle; thus, it is used often in microirrigation systems. Powd ered calcium hypochlorite (CaCOC12), also called high test hypochlorite, is often used in swimming pools, but is not recommended for injection into microirrigation systems. Calcium hypochlorite can produce precipitates that can clog emitters, especially at high pH levels. Chlorine gas has the advantages of low cost and a chemical reaction in water that is acid-forming, thus preventing precipitation of dissolved minerals. However, chlorine gas can be fatal if inhaled and may not be labeled for use in irrigation systems in all states.
Chlorine injection schedules may vary depending on water quality and clogging problems. H.W. Ford in 1979 developed a key that recommends NAOC1 injection rates and schedules for Florida conditions. G.A. Clark and A.G. Smajstrla in 1992 presented tables from which injection rates can be read to achieve desired concentrations in irrigation systems.
Because many factors affect the chemical reactions of chlorine in an irrigation system, recommended injection schedules will only be approximate. Adjustments in injection rates should be based on measured free residual chlorine concentrations in the system. The D.P.D. test kit should be used to measure the free residual chlorine concentration at the distant end of the system. The injected concentration should be adjusted until a small amount (0.5 to 1 ppm) of free residual chlorine is detected.
Chlorination is less effective at high pH, and it is relatively ineffective at pH levels above 7.5. Thus, acid injections might be necessary to lower the water pH in order to increase the effectiveness of chlorine.
Acid Injection: Acid is injected into microirrigation systems to lower the pH of the water for two purposes: 1) to reduce chemical precipitation; and 2) increase the effectiveness of chlorine. Sulfuric, hydrochloric and phosphoric acids are all used for this purpose.
Recommended injection rates and procedures were given by G. Kidder and E.A. Hanlon in 1985. The amount to be injected depends on the irrigation water quality, specifically the concentration of bases per unit of water volume. They recommended injecting acid at rates to neutralize 80 percent of the bases, which will normally result in dropping to pH to the range of 4.5 to 5 immediately after injection. This range is adequate for many applications, but higher values might be acceptable to prevent precipitation during continuous injections. Lower concentrations may be required for slug treatments to dissolve accumulated scale. A pH meter should be used to verify that the desired pH range is achieved and to adjust injection rates if it is not.
Acid injection rates should be precisely controlled by using calibrated acid-resistant injection pumps that are accurate in the range of flow rates to be injected. Extreme care should be taken to avoid being injured during acid injection. Always wear goggles and chemical-resistant clothing. Dilute acids by pouring the acid into water - never pour water into acid because it will splatter. Do not mix acid and chlorine formulations because their chemical reaction can produce dangerous chlorine gas. Inject acids at least several feet upstream of the chlorine injection point. Flush the injection system with water after injection.
Scale Inhibitors: Chelating and sequestering agents are sometimes used to help prevent emitter clogging from chemical precipitates. An organic polyphosphate such as sodium hexametaphosphate is used for this purpose. These agents do not prevent the formation of precipitates; however, they limit the growth of particle sizes to the microscopic level. Then, these small particles are readily discharged through emitters without clogging.
Sodium hexametaphosphate is widely used because small amounts injected are effective against deposition of carbonate, iron and manganese precipitates. Normally 2 to 4 ppm is required for each ppm of iron or manganese. These types of polyphosphates are often used because they are relatively inexpensive, readily soluble in water, nontoxic and effective at low injection rates.
System Design: To prevent emitter clogging, microirrigation systems must be properly designed. The components must be assembled as a system, with compatible components throughout the system. Emitter selection is very important. Turbulent flow emitters have very desirable flow characteristics with respect to emitter clogging. The turbulent flow process permits emitter passageways to be larger than laminar flow devices, and the turbulence helps to prevent the deposition of small particles in emitter passageways.
Filtration systems must be selected based on minimum size of emitter passageways. All system components must be compatible with the water quality, including fertilizers, acids or other chemicals to be injected in order to prevent corrosion or other deterioration of components. Other chemical injection systems must be provided as needed, including chemical injectors for chlorine, acid or scale inhibitors, depending on water quality.
All components must be properly installed in order to function as designed. For example, PVC pipe must be buried or otherwise protected from the deteriorating effects of sunlight and to prevent algae growth in the pipelines. Flush valves must be large enough to permit flushing velocities that are large enough to remove sediment from pipelines.
System Management Plan: To prevent emitter clogging, microirrigation systems must be properly managed. Even the best system design will not prevent emitter clogging if required maintenance operations are not performed as needed. A first approximation of a regular maintenance schedule should be developed when the system is designed. This schedule should then be adjusted as field experience is gained.
A maintenance schedule should include flushing of filters, chemical injections, flushing of pipelines and routine system inspections, checks of flow rates, pressures and emitter performance. Filters should be flushed whenever filter clogging is indicated by pressure losses that are substantially increased (5 to 10 psi above normal) across the filter. This can be done manually, but is most efficiently done using a differential pressure switch and automatic valves.
As previously discussed, chemicals should be injected as needed based on laboratory water quality analyses and in-field tests (free residual chlorine, pH and the like) to measure the effectiveness of the injection practice. Injection schedules may need to be adjusted depending on the irrigation schedules or other factors such as algae blooms in the irrigation water source.
Pipelines should be flushed as needed, based on the appearance of the flushed water. Mainlines should be flushed first, followed by manifolds, then laterals. Flushing should occur until the water runs clear for one or two minutes. In extreme cases, automatic flush valves can be installed to flush laterals at the start of each irrigation.
Routine system inspections should be performed to ensure all components are functioning as designed and that clogging does not occur. This requires visual inspections for leaks or other component failures, and reading pressure gauges and flow meters to ensure that design flow rates are being met. The combination of pressure increase and flow rate reduction may indicate emitter clogging problems. Individual emitters should be randomly inspected in the field for evidence of clogging such as buildup of precipitates or sludges. Emitter flow rates can be determined during irrigation using a volumetric container and stopwatch to measure the volume collected per unit time.
A microirrigation maintenance program should be designed to prevent emitter clogging. It should be flexible and result in changes in maintenance schedules if clogging begins to occur. It is often very difficult or impossible to recover emitters that have become completely clogged; thus, the ideal maintenance program should be directed at prevention of emitter clogging rather than attempting to recover clogged systems.
Summary: The success of microirrigation depends directly on the ability of the system manager to prevent emitter clogging. Clogging can occur from particulate matter, biological growths and chemical precipitation, especially when fertilizers or other chemicals are injected into systems.
A properly designed microirrigation system must include provisions to prevent emitter clogging. These provisions may include a water quality analysis to identify the severity of the clogging problem anticipated, a filtration system, aeration/settling ponds, a system for flushing pipelines and a chemical water treatment system. Chemical water treatment may require the injection of chlorine, acid or scale inhibitors.
Poor quality irrigation water may cause clogging. However, poor system design and management can also cause or contribute to clogging. Thus, proper microirrigation system design requires proper selection and installation of emitters and other components and a system management plan to prevent clogging.
Allen Smajstrla is a professor of agricultural engineering at the University
of Floride, Gainesville, where he has worked for the last 16 years. He
also will co-chair the Fifth International Microirrigation Congress to
be held April 2-6 in Orlando, FL. This article originally appeared in the
1994 Irrigation Association Technical Conference Proceedings. Reprinted
with author's permission.
An irrigation system works most effectively when it distributes the right amount of water uniformly.
What is involved in an evaluation?
The evaluation has two parts. The main part is a check of the system known as an annual survey. The annual survey is a "season-long" look at how well a grower's irrigation system operates. The other part is an actual field test of the system. The field test supplies some of the information used in the annual survey.
How does an evaluation work?
The annual survey identifies operating problems and places a dollar value on them. The survey estimates annual power and water costs under current irrigation system operations. The survey assigns a dollar value to specific problems found in the operation of the irrigation system. The grower can use these values to estimate savings as each problem is corrected. The grower can also identify which problems, when corrected, give the greatest return.
The grower provides most of the information needed for the survey during an interview. The interviewer asks questions about the irrigation system, water supply, and energy and water costs. Having good water records is important. Sometimes the survey cannot be completed because the grower does not have the information. When that happens, the value of the survey is pointing out what records should be kept.
The second part of the evaluation is an actual field test of the system.
How can an evaluation save money and resources?
Energy, water, and fertilizer use generally go "hand-in-hand" in production agriculture. When water use goes up, energy use goes up, and so do other costs. If the amount of water required for crop growth is not applied uniformly, some plants receive too much, and others receive too little water and fertilizer.
Some studies show that growers want to be on the safe side and may apply more water to the entire field. The result is plants previously receiving too little water get enough, while the rest receive too much. A 75 percent distribution uniformity, generally considered good, means some parts of the field can still receive twice as much water as other parts. Over application of irrigation water may result in fertilizer leaching and subsurface drainage problems.
What does poor uniformity cost?
Poor uniformity could result in higher water, energy, and fertilizer bills and lower crop production. When water moves below the crop root zone, the fertilizer moves, too. However, good uniformity benefits crop growth, yield quality, and harvest profits.
What does an irrigation evaluation involve?
All requests for irrigation system evaluations are serviced in the order they are received. Each request is serviced by a water management team. This team consists of a member of the SCS engineering staff, SCS field office and possibly a member of the local soil conservation district. Ideally, the team leader would be the leader of the proposed mobile lab.
An irrigation system evaluation starts by meeting the manager or irrigator at the site to be tested. An interview with the manager or irrigator obtains a history of the system including: how the system is operated, the type of irrigation scheduling method used, and any long or short term problems encountered.
The team then collects the following information:
1. Check the condition and operation of the filter, fertilizer injector and booster pump. (All or some of the items may or may not be present on a particular irrigation system.)
2. Record sprinkler/emitter flows at various locations on the system. The number of flows collected varies depending on the size of the system. As flow measurements are being collected, differences in sprinkler/emitter models and types used are also noted.
3. Record system pressures at various locations on the system. As with taking flow data, the number of locations tested is dependent on the size of the system.
4. Determine the amount of soil wetted by each emitter or sprinkler.
Once this information is collected, the system is turned off and the following is gathered:
1. Crop spacing.
2. Soil water holding capacity.
3. An estimate of crop maturity and condition.
All this information is taken to the office or mobile lab where the report is compiled. Flow and pressure data is used to calculate system uniformity. Flow data is used to calculate the flow rate of the sprinklers or emitters. Problems noted during the evaluation are included in the report with recommendations on how to correct them. If the system is in good condition, a baseline irrigation schedule is also included. This schedule is set up around the conditions observed during the evaluation (soil type, sprinkler output, crop spacing and maturity, etc.) This schedule gives the grower a good idea of the crop's basic water needs.
The report is returned, in person, to the grower. This allows open discussion on the method used to obtain results and how the information should be used. It allows the grower to ask questions and make comments as needed.
Irrigated acreage in New Jersey - 1993
Sprinkler - 87,700 acres
Center Pivot/Linear Move - 3,730
Traveler - 46,650
Solid Set - 15,860
Hand Move - 21,460
Low Flow - 6,000
Micro-Spray (surface) - 100
Drip (surface) - 5,900
Type of irrigation power units
Diesel 65%
Electric 25%
Gasoline 10%
Number of irrigation wells: N/A
Average depth - 200'
Acreage irrigated by crop
Field crops - 4,680
Nursery - 5,190
Small fruits, nuts - 7,735
Sod (Turf) - 6,715
Tree fruits - 12,310
Vegetables - 57,070
SOURCE: Craig Storlie, Ext. Agric. Engineer
Rutgers R&D Center
Bridgeton, NJ 08302
Common system problems
System pressure - Gravity takes a toll on water delivery. As water moves uphill, it losses pressure and as it moves downhill it gains pressure. If there is no pressure regulation present, often the top of the hill has inadequate pressure and the bottom of the hill has excessive pressure. Because water pressure greatly affects sprinkler flow, this translates into low sprinkler flow at the top and high sprinkler flow at the bottom. This variation in sprinkler or emitter flow adversely affects system uniformity.
Sprinklers/Emitters - A common problem is mixed sprinklers or emitters within an irrigation block. Micro sprinklers and jets are usually small and often look very much alike. Sometimes the only difference between them is the color of the orifice or possibly some small markings. While the irrigation system might have been originally installed with one type of sprinkler or emitter, things can change. In time, sprinklers and emitters break and are replaced. As the irrigators walk the field, they may feel that a particular plant needs more or less water than the others and changes the sprinkler or emitter. In a few years a system can have a mixture of sprinklers and emitters present with each different model and orifice size having a different gallons per hour output. Mixing sprinklers and emitters lowers uniformity by applying different amounts of water to different plants within a single area.
The best place to start is with the specification sheet provided by the sprinkler manufacturer. However, manufacturers' data on sprinklers is gathered under controlled, laboratory conditions. Sprinkler age, water pressure and water quality will affect its output. Sprinklers and emitters should be tested under normal operating conditions to determine output. An irrigation system evaluation will provide this information.
Irrigation scheduling - Irrigation scheduling is the practice of replacing water in the soil that has been removed by the crop, lost to surface evaporation and lost to deep percolation. To correctly schedule irrigations, growers need to ask themselves the following questions:
What is the average seasonal water requirements of my crop?
How mature is my crop?
How healthy is my crop?
What are the typical seasonal climatic conditions in this area?
What is the output of my irrigation system?
What is the uniformity of my irrigation system?
What is my soil's water holding capacity?'
How much area is wetted by my irrigation system?
What is the quality of the water I am applying?
Common irrigation scheduling methods
Guess method - There is no basis to irrigation frequency and duration other than a good guess.
Do what the neighbor does - This is fine if you have exactly the same conditions as your neighbor - same type of crop, same emitters or sprinklers, same water pressure, same soil type, etc. Then you have to assume that your neighbor's schedule is correct - it may or may not be. Irrigation schedules work best when they are tailored to specific conditions.
Calendar method - The calendar method involves irrigating according to a set calendar increment - once a week, every other day, etc. Irrigation frequency and duration may be adjusted according to historical weather patterns, current weather conditions or a combination of both. Some growers are successful while others are not.
Soil based methods - Soil based irrigation scheduling involves monitoring the soil's moisture level. When the moisture level reaches a given point, it is time to irrigate again. The simplest way to monitor soil moisture is with a shovel or soil probe. The soil is sampled in a given location and the moisture level is determined by how it feels. This method works fine with practice.
Another method of estimating soil moisture is with a tensiometer. A tensiometer is a plastic tube with a porous tip. The tube is filled with water, sealed and placed into the ground at a desired depth. As the soil dries out, it tries to pull water out of the tube through the porous tip. The suction causes a gauge mounted on the tube to move. When water is put back into the soil through irrigation or rainfall, the suction is relieved and the reading of the gauge reduces. This method requires some calibration and must be monitored almost daily at certain times of the growing season.
A neutron probe soil moisture gauge is also available. The cost and need to receive approved radioactive training removes this tool from the reach of most growers. A neutron probe can help determine soil moisture levels at levels between field capacity and permanent wilt point. A neutron probe can also "show" the developing root system by "observing" soil depletion profiles.
R.I.S.E. - R.I.S.E. or Resource Information Serving Everyone, is a series of weather stations located in Gloucester and Atlantic counties and proposed throughout the state. This allows growers to schedule irrigations based on daily climatic conditions. R.I.S.E. stations report reference evapotranspiration or Et. Et is a measure of how much water an actively growing uncut pasture would use on a given day. Growers then use a crop coefficient or Kc to convert this data into a form useful to the crop they are growing. R.I.S.E. can be a very effective irrigation scheduling tool when used correctly. It does take time to learn how to use it and make adjustments to correspond to the farm's location. It also requires a grower to have a computer, modem and communication software. Input from the SCS is needed.
Despite all of the technology available today, there is no one fool proof method of irrigation scheduling. There is also no substitute to walking the field and observing how the crop reacts to changing climatic conditions.
Wetted Area
Wetted area is a term used to describe the amount of soil wetted during irrigation. Wetted area is rarely a problem in furrow, border strip or impact sprinkler irrigation. It is often a problem in micro irrigation or drip. Micro or drip irrigation systems usually wet only part of the total soil area occupied by the crop. The smaller the wetted area, the less water storage the crop has to draw from. Common problems affecting wetted area include:
Sprinkler or emitter too small for crop maturity - As a crop matures, it requires more water. Trees are often established with small sprinklers because of their small root zone. As the tree matures, the sprinkler should be replaced with a model that has a higher output and larger throw.
A small wetted area can also cause poor mechanical stability by allowing a small root zone to develop. This reduced root zone may not be able to support the weight of the plant.
Sprinkler or emitter interference - This can be anything that obstructs the pattern of the sprinkler or emitter. This includes risers that are tilted at severe angles, risers that are too short, risers too close to the plant, weeds, low branches or other obstructions that block the sprinkler or emitter.
System Maintenance
Like anything mechanical, irrigation system components can and do break down. Routine maintenance will help to lessen the effects and frequency of component failure. Common maintenance procedures include:
Filter operation - The quality of irrigation water varies around the state and within individual localities. A filter may be required if the system uses well water, water that has been held in a reservoir or uses a fertilizer injector. Filters require periodic maintenance to remove accumulated material. If a filter is allowed to accumulate a large amount of material, severe pressure reduction can result. Filter cleaning frequency will vary depending on the quality of irrigation water used, however a pressure drop of five to ten pounds between filter inlet and outlet indicate a need for cleaning.
Line flushing - Even the best filters allow some foreign material to enter the irrigation system. This material usually collects near the low ends of lateral lines. If allowed to accumulate, emitter or sprinkler plugging or total loss of water can occur. To correct this problem occasionally open lateral line ends - with the system running - until clear water flows.
Walk lateral lines - Sunlight and age have effects on plastic. Anything plastic will deteriorate over time when exposed to sunlight. Foreign material carried in irrigation water often has abrasive qualities that can wear down and clog emitters and sprinklers. By walking an irrigation system, pipe leaks, clogged emitters and broken sprinklers can be found before they cause serious problems.
System design - Problems caused by faulty system design can be difficult and frustrating to diagnose. When an irrigation system is correctly designed, the pipe used is sized to handle a specific amount of water flow. If more water is put through an irrigation system than it was designed to handle, excessive friction loss can result. If enough unwanted friction loss occurs, system pressures can be reduced causing a loss of system performance.
Retrofit of irrigation systems - A drip irrigation system converted to micro sprinklers or vise versa, can cause problems. The increased water flow caused by larger flow into sprinklers can cause excessive friction loss and a subsequent loss of performance. Similar problems can occur when an irrigation system is extended into a newly planted area or a new pumping plant is installed.
System designed poorly from the start - Some systems have been designed wrong from the very start. The system may have been designed by someone who was not familiar with water hydraulics or, a correct design may have been altered or incorrectly installed. In any event, poor system performance usually results.
Successful growers are a great source of information. However, each field is unique - each has a different combination of crops, climate, soils, topography, etc. Growers should never assume that irrigation practices that work for their neighbor will work for them as well.
For the most part, professional growers tend to be more conscientious of their irrigation practices. Farming is the primary source of income. Because of the amounts of money involved in farming, these growers can often not afford to float losses year after year that are attributed to poor farming practices.
It is the aim of the South Jersey RC&D Council and the Soil Conservation
Service to provide growers with practical information and assistance needed
to keep their irrigation systems operating as effectively as possible.
Smart irrigation water management makes good business sense. The future
of agriculture in New Jersey depends on it.
BY THE USDA-SOIL CONSERVATION SERVICE, CHESTER, PA
MARCH 1993
INTRODUCTION
As the saying goes, "The buck stops here." How true this is for local officials. You represent your constituents who want certain actions to happen relating to land use and water quality. Various groups from those pushing development to those protecting the environment put pressure on you - each wanting their agenda carried out. In addition, state and federal agencies have regulations that you must support.
Out of all these differing viewpoints, you, the local official, must make the final decision on how the land is used and how your area develops. Keeping the local economy viable, while at the same time sustaining the land and water for the future, could be described as "walking a tightrope." This publication provides information on land use options for protecting soil and water resources. It is provided as reference to help you make better informed land use decisions.
SOIL EROSION
Soil erosion is usually caused by the impact of water falling as raindrops and by the force of water flowing over the land surface.
Raindrops falling on bare soil detach soil particles. Water running in a sheet on the surface of the ground picks up these particles and carries them along as it flows downhill towards a stream. As runoff gains in volume and velocity, it detaches more soil particles, cuts rills and gullies, and adds to its sediment load.
The greater the distance the water runs uncontrolled, the greater its erosive force and the greater the resulting damage. In addition, getting runoff under control becomes increasingly difficult.
Soil erosion is also caused by the force of wind blowing across unprotected ground. The wind-borne sediments land in streams, roads and neighboring lands.
SEDIMENTATION
The settling out of the water-transported soil particles is called sedimentation. The process occurs when the water velocity is slowed enough to allow soil particles to settle out.
FACTORS WHICH INFLUENCE EROSION LOSSES
Erosion and resulting sedimentation generally occur only when the soil is disturbed. The extent of erosion is determined by topography, size of the area, soils, climate including rainfall duration and intensity, and the degree of vegetative cover.
Topography
Slope length and steepness are key elements in determining the volume and velocity of runoff and thus, the degree of erosion. As both slope length and grade increase, the rate of runoff increases, and the potential for erosion intensifies.
Slopes without vegetation must be protected from runoff and re-established as quickly as possible. If possible, steep slopes should not be disturbed. By limiting the length and gradient of slopes created or modified during development, runoff velocities can be reduced and erosion hazards minimized.
Soils
The vulnerability of a soil to erosion is known as its erodibility. Soils that contain a high proportion of silt and very fine sand are the most erodible. Erodibility of soil decreases as the percentage of clay and/or organic matter increases. Both act as a binder between soil particles.
Clayey soils have a very high water holding capacity compared to sands and gravels, but poor infiltration characteristics. In this respect, the clayey soils are vulnerable to erosion because they tend to have a higher rate of runoff.
"Well-graded" soils are those which contain a wide range of particle sizes. Well drained and well-graded gravels and gravel-sand mixtures with little or no silt have low erodibility to sheet flow, but erode easily under concentrated flow. Coarse, granular soils also have high permeability and sufficiently good infiltration capacity to reduce runoff.
Soils information is found in soil surveys, usually published as county reports. Soil surveys are scientific inventories based on soil properties. A county soil survey report includes aerial photographs with the soils indicated for all the land area. Interpretative tables provide soil properties and suitability for many different uses, both agricultural and urban. These reports are published by the Soil Conservation Service in cooperation with state land grant universities.
Vegetative Cover
Vegetative cover is important in controlling erosion. It shields the soil surface from the impact of falling rain, holds soil particles in place, maintains the soil's capacity to absorb water, and slows the velocity of runoff.
Climate
The frequency, intensity and duration of rainfall are fundamental factors in determining the amounts of runoff produced. The capacity to detach and transport soil particles rises with the increase in volume and velocity of runoff.
EROSION AND SEDIMENT CONTROL
Five Principles of Erosion and Sediment Control
The five major principles of erosion and sediment control are:
1. Keep the disturbed areas small. The development plan should be prepared with a minimum of clearing and grading. Natural cover should be retained and protected whenever possible. Critically erodible soil, steep slopes, streambanks and drainageways should be protected.
2. Stabilize disturbed areas as soon as possible. Two methods are available: structural and vegetative. Structural is a constructed measure such as a diversion, a storage basin, a stone-lined channel, etc. Vegetative is mulching and seeding with grass, scrubs and/or trees.
3. Keep water runoff velocities low. The removal of existing vegetative cover during development and the increase in impermeable surfaces after development will add to both the volume and velocity of runoff. Ways to control this runoff must be included in the development plan. This includes runoff diversion and storage.
4. Protect disturbed areas from water runoff. Conservation measures can be used to prevent water from entering and running over the disturbed areas. Diversions and other control structures intercept runoff and either store or divert it away from vulnerable areas to stable outlets.
5. Retain sediment within the site area. Sediment can be retained by two methods: filtering runoff or detaining it. Filtering can be done with filter fabric, straw bales and/or finely graded gravel. Detaining uses a storage basin that contains the runoff until many of the sediments drop out. However, the best way to control sediment is to prevent erosion.
COMMON EROSION AND SEDIMENT CONTROL PRACTICES
STORMWATER MANAGEMENT
Municipalities today must address stormwater management as critical to protecting water quantity and quality. Development increases the amount of impervious surfaces in an area. The impervious areas include sidewalks, parking lots, driveways, streets and building roofs.
The loss of natural ground cover increases the volume of stormwater runoff in a watershed. The goal of good stormwater management is to have no more runoff water leave the site after development as compared to the area under natural conditions.
The Soil Conservation Service has developed a system for controlling runoff in developing areas. Primary purposes are to:
Minimize flooding.
Handle storm discharges in a safe manner.
Keep erosion and sedimentation to a minimum.
COMMON STORMWATER MANAGEMENT PRACTICES
CRITICAL AREA TREATMENT
A "critical area" is a localized area that has an excessively high soil erosion potential. Size may vary from less than an acre to many acres, but all have a common denominator - they are highly erosive and produce large amounts of sediment.
Usually, the area contains a combination of the following factors: unstable soils, steep slopes, subsurface water seepage, and/or a lack of adequate ground cover. Erosion rates in excess of 40 tons per acre annually are not uncommon on critical areas.
Critical areas include, but are not limited to: steep escarpments, abandoned strip mines and pits, roadbanks, streambanks, and soils subject to slippage.
Critical area treatment must be carefully planned and designed to treat the following causes of the accelerated erosion:
Surface Flows - Structures such as diversions and drop inlet structures are used to channel flows away from the critical area.
Internal Seepage Water - Subsurface drains are used to remove the water before it becomes a problem.
Steep Slopes - Grading to a more stable slope is one solution. If grading is not practical, structural measures such as rock riprap, gabion rock-filled baskets or retaining walls may be used.
Ground Cover - Deep rooted shrubs and trees are used where the problem is not severe. Sometimes shrubs are used with structural measures - this is called bioengineering. In all cases, bare and disturbed soils require an adapted cover: grasses, legumes, stone mulch, shrubs and/or trees. The key is determining what is causing the excessive erosion and then applying the needed structural or vegetative corrective measures. A knowledge of soils, plants and engineering is needed for critical area treatment.
WETLANDS
Wetlands are areas that have three characteristics: 1) standing water or water saturated to the surface at least two weeks during the growing season for most years; 2) soils with a high water table; and 3) water-loving plants.
Wetlands provide many beneficial purposes. Surface water is purified as it passes through the wetland. Sediments are trapped, also improving water quality. Wetlands are home to many types of wildlife including waterfowl. Wetlands help recharge ground water supplies. And lastly, because they slow runoff and can store rainfall, they reduce downstream flooding.
For these reasons, wetlands are protected against filling and/or draining. A proposed change in a wetland must be approved and permits issued before any work can start. Approving state agencies vary by state. Federal agencies having review and approval authority for wetlands under various circumstances include the Environmental Protection Agency, the Army Corps of Engineers, the Fish and Wildlife Service and the Soil Conservation Service.
Artificial wetlands can also be constructed to avoid or reduce damage to water quality. The use of constructed wetlands is an emerging technology that is gaining in popularity for water quality maintenance or enhancement.
Contact any of the above agencies with questions or for additional information relating to wetlands.
WATER BODIES
Water bodies are streams, ponds, lakes, and larger areas such as bays. Much of the water in these bodies reach them by way of overland flow.
The quality of the body of water is affected by two types of pollution: 1) point source, and 2) nonpoint source.
Point source pollution is that which comes from a specific discharge point such as a pipe. Pipe discharges come from sewage and industrial treatment facilities. Untreated pipe discharges come from municipal storm sewers, roads and highways, individual homesites without a proper on-site treatment facility, and some industries and businesses.
Nonpoint source pollution is defined as runoff and seepage. Runoff comes from towns, suburban homesites, farmland, woodlands and idle land. Seepage into streams and lakes may come from nearby homes with inadequate on-site sewage systems or from farms, businesses and industries with improper waste storage and handling procedures.
Both forms of pollution have serious detrimental effects on water quality. Local officials are the "key players" in protecting and improving water quality in water bodies. They are the implementers of state and federal regulations and laws.
There are numerous state and federal agencies who are able to assist local officials in matters relating to water quality. They include such agencies as the Environmental Protection Agency, The U.S. Army Corps of Engineers, Soil Conservation Service and state water quality agencies. Use them to increase your effectiveness and to help protect the environmental quality of your community.
Irrigation Journal, PO Box 2180, Cathedral City, CA 92235-2180
Drip irrigation of row crops increased considerably in California over the past few years. Drip irrigation can increase crop yields, reduce water use, precisely apply both water and chemicals to the rootzone at both a high frequency and a high uniformity, and reduce fertilizer and cultural costs.
Drip irrigation, however, is expensive to install and maintain. Because of the interest in drip irrigation of row crops, an overview on practices and research results on drip irrigation of row crops is provided. Information in this overview was developed from grower experiences, field evaluations of drip systems, research results in California and a review of literature on drip irrigation.
System Design
Drip irrigation systems can apply water uniformly. Results from field evaluations of microirrigation systems (drip tape, drip emitters or microsprinkler systems), however, revealed many systems to be operating far below their potential for uniform water applications due to excessive variability in emmiter-discharge rates. Excessive pressure triggered by clogged emitters caused this variability.
The emission uniformity describes how uniform irrigation water is applied by drip systems. It is the minimum amount of applied water (lowest one-fourth of the measured emitter-discharge rates) divided by the average discharge rate. Results from the field evaluations and computer-design evaluations and computer-design evaluations of drip irrigation systems show that the fieldwide emission uniformity should be between 80 and 90 percent, and that the emission uniformity along the lateral should be between 90 to 95 percent.
Emitter Spacing
Emitter spacings available in drip tape generally range between 4 and 24 inches, but larger spacings are available in drip tubing. Most growers use spacings between 8 and 18 inches. Strawberry growers use an 8-inch spacing.
Little relationship exists between emitter spacing and crop yield, based on a literature review. Results of recently completed research at the University of California Westside Research and Extension Center in Fresno County showed no yield effect for tomatoes and melons for emitter spacings of 12, 16 and 24 inches (tape depths were 8 and 12 inches). Three years of data on cotton, however, showed larger cotton yields for the larger emitter spacing (24 inches). Tape depths were 8 and 12 inches.
Depth of Tape
Options for depth of drip tape include surface, shallow (4 to 12 inches) and deep installation (more than 12 inches). Surface installed tape is easier to install and repair, but it is highly susceptible to damage from wildlife and human activities. The tape must be removed prior to harvest and then reinstalled.
The shallow installation is less susceptible to damage from wildlife and other field activities, but tillage practices must be modified to prevent damage to the drip tape. The deep installation is more difficult to install and repair, but tillage practices require little modification. Shallow-rooted crops are not recommended to be grown under a deep installation, and another irrigation method may be needed for stand establishment.
Subsurface or buried drip is normally used for row crops. The desired depth of tape depends on soil type, root distribution of crops (including crop rotation), seed germination, soil salinity and surface wetting. Depths of installation for vegetables generally range between 6 and 10 inches. Depths used for strawberries commonly range between 1 and 3 inches. Few, if any, drip systems are installed deeper than 12 inches, although some researchers have used an 18-inch depth. More depth may be appropriate for crops such as sugar beets and potatoes.
Less evaporation occurs for the deep-tape installation than for the shallow - or surface-installed tape, and thus more water should be available for crop transpiration. Higher yields, in turn, should occur. A literature review of studies on crop yield vs. depth of tape revealed mixed results. Some data showed higher yields for deep-rooted crops, such as cotton and tomatoes, with tape installed deeply (18 inches) compared to surface installation, while other data showed little difference. A small number of studies on shallow-rooted crops showed no yield difference between surface and shallow installations. However, one study showed smaller onion yields for a subsurface system buried 10 inches compared to surface drip. Smaller yields of shallow-rooted crops might be expected with deep systems because most of the roots of these crops would be above the tape.
Seed Germination
Surface drip irrigation can be used for seed germination; however, several concerns exist for seed germination with subsurface drip irrigation. First, upward movement of water from the drip tape must occur. This upward flow depends on the depth of tape, soil type, emitter spacing and discharge rate. A literature review and grower experiences suggest that seed germination is possible for tape depths under 10 inches with emitter spacing of 12 inches, providing a good seed bed exists and soil salinity is not a problem. However, one grower germinates with a subsurface drip system with a tape depth of 12 inches in a sandy loam.
Seed depth is also a concern. One study showed good germination of tomatoes for seed depths under 1.5 inches for drip tape buried at three depths ranging between 6 inches and 12 inches. Poor germination occurred from a seed depth of 2.5 inches.
Soil salinity near the surface poses a major hazard to seed germination with subsurface drip irrigation occurs due to water and salts moving above the drip tape. These near-surface salts must be leached either by rainfall or sprinkler irrigation before planting.
Irrigation Frequency
High-frequency irrigation is recommended under drip irrigation. Results of a literature review, however, revealed no consistent trends between irrigation frequency and crop yield for irrigation frequencies ranging from eight times per day to once per week.
Ongoing research at the UC Westside Research and Extension center on vegetable crops thus far show no relationship between tomato yield and irrigation frequency for frequencies of twice per day, once per day, twice per week and once per week. A smaller onion yield occurred under the once-weekly irrigation. Research is continuing on lettuce and peppers.
Reduced emission uniformity can occur for high irrigation frequencies (several times per day). For these frequencies, pipelines and laterals are filled and drained for each irrigation. The frequent drainage of the pipelines and laterals can reduce the emission uniformity.
Clogging
Clogging of emitter reduces the emission uniformity (EU) of a drip system with an initially high-design EU. Common sources of clogging are suspended materials in water, precipitation of carbonates and precipitates from fertilizer injection (can occur in all microirrigation systems), root intrusion and soil ingestion. The latter two causes occur in buried drip systems.
Injection of fertilizers can cause clogging. Phosphate fertilizers can react with calcium and magnesium to form insoluble phosphate precipitates in the irrigation water containing at least 2 to 3 meq/l of calcium and magnesium. Calcium-based fertilizers can react with bicarbonate in the irrigation water to form calcium carbonate precipitates in water containing at least 2 meq/l of bicarbonate. Anhydrous and aqueous ammonia can increase the pH of the irrigation water, causing precipitation of calcium carbonate.
Root intrusion also can clog subsurface drain systems. Roots tend to grow along the seam. A study conducted in Hawaii suggests that emitter design may be a significant factor in root intrusion. While little data exist on this problem, some preventive measures included application of chlorine, phosphoric acid or N-furic to the water. A drip tape impregnated with a herbicide to prevent root intrusion is also available. Applying adequate water is one practice used to minimize root intrusion. Some manufacturers are designing drip tape with the emitter opening placed away from the seam of the tape.
Soil ingestion can occur during drainage of the system after an irrigation, particularly on steep slopes. The saturated soil next to the emitter prevents air from entering the lateral during drainage. A vacuum then can develop in the lateral that can ingest soil through the emitter. This material becomes deposited in the emitter and eventually can be deposited along the lower end of the lateral. Field experiences suggest that factors contributing to soil ingestion include the size of emitter openings, soil type, slope and length of the lateral. Soil ingestion can be reduced by installing vacuum relief valves at the upper end of the laterals, although some vacuum will occur if the relief valves are installed on buried manifolds or submains. Periodic flushing of laterals is required to remove any deposited material.
Recommended flow rates at the end of the lateral for flushing are 1 GPM for 5/8-inch diameter tape/tubing and 2 GPM for 7/8-inch-diameter tape/tubing. Lateral flow rates will be larger during flushing than during irrigation, requiring fewer laterals operated per flushing set than operated during an irrigation set.
Salinity
Salinity may be a problem with subsurface drip irrigation. Above the drip tape, no leaching will occur during irrigation, and salts will accumulate during the irrigation season. Extremely high salt concentrations exceeding 10 dS/m have been found in the first few inches below the soil surface for irrigation water with an electrical conductivity of 2.2 dS/m. Below the drip tape, leaching will occur during an irrigation. Maximum leaching will occur in the immediate area and below the tape. Leaching will decrease with horizontal distance from the tape with little or no leaching midway between laterals.
Leaching above the drip tape must be done with another irrigation method or with rainfall. The applied water must move the accumulated salts below the drip tape, where downward-moving water applied by the drip tape will continue to leach salts from the rootzone. The deeper the tape, the more water is needed to move the salts below the tape. Accumulated surface salts not leached below the drip tape will move back up toward the soil surface.
Bed shaping also is used to control salinity. Before planting, the bed surface is raised above that normally used for planting. The drip system is then operated, moving the salts into the raised portion of the bed. The raised portion containing the accumulated salts, which will be concentrated in the first few inches of soil, is then removed prior to planting.
The depth of the tape should be considered for salinity management. Studies in the Santa Maria Valley and near Davis have shown that low salinity occurs near the drip tape. The higher the field-wide leaching fraction, the larger the volume of low-salinity soil near the drip tape. Most of the root pattern will be in the low-salinity soil for shallow-rooted crops for tapes installed at shallow depths. For deep depths, the low-salinity soil may be below most of the roots, particularly for shallow-rooted vegetable crops.
Does Drip Irrigation Pay?
The actual economic benefits and costs of converting to drip irrigation are difficult to predict and are site-specific. Experiences in Arizona on converting from furrow to drip irrigation of cotton have been used to promote drip irrigation of row crops in California. However, in Arizona nearly 80 to 90 inches of water were applied by furrow irrigation on sandy soils for cotton, far more than normally applied by furrow irrigation in California. Converting to drip irrigation reduced the applied water by about one half and increased yields, thus making drip irrigation more profitable in Arizona.
Mixed results have been found in California. Results from field-scale comparisons of drip irrigation and furrow irrigation of cotton in the San Joaquin Valley have shown that higher yields sometimes occurred under the drip system, but other times yields were the same for the drip and furrow systems. With one exception, less water was applied with the drip systems. However, profits generally were higher for the furrow systems than for the drip systems.
A field demonstration in the Salinas Valley comparing furrow, surface drip and subsurface drip irrigation found little difference in lettuce yield among the three systems. The drip systems used 2.1 to 5.7 inches less water than the furrow system, but water savings alone could not economically justify converting to drip irrigation.
A more recent field-scale comparison of furrow vs. drip irrigation of processing tomatoes found the same yields for one variety and 2.4 tons per acre more for the drip system for another variety. About 11 inches more water were applied by the furrow system.
Grower experiences in converting from furrow to drip irrigation of row crops are mixed in terms of benefits. Some growers experienced higher yields, while others did not. Some vegetable growers, however, have reported $10 to $200 in savings in cultural costs per acre.
Use Caution
Many claims about the benefits of drip irrigation have been made. These claims may be valid under some circumstances but not under others. Field experiences indicate that the benefits of drip irrigation are site-specific and are difficult to predict with any degree of reliability. Converting from a marginally designed and managed furrow system to a drip system may not realize substantial benefits. Converting from an efficient furrow system to a drip system may not pay.
Because of the uncertainty in the amount of benefits in converting to drip irrigation, we recommend initially converting a small acreage to drip irrigation to see if drip irrigation will pay under your site-specific conditions. If it pays, then increase the acres under drip.
Blaine Hanson is an irrigation and drainage specialist, Department of Land and Air Water Resources, University of California, Davis. Don May and Dan Munk are farm advisers at the University of California Cooperative Extension, Fresno. Allen Fulton serves as a farm adviser in Kings County. Warren Bendixen works as farm adviser in Santa Barbara County.
A manual, Drip Irrigation for Row Crops, is available for growers, published
by the University of California. The manual contains more detailed information
on the above products. The manual is $15 and can be ordered from Janice
Heine, LAWR, UC Davis, Davis, CA95616. Checks should be made payable to
the University of California Regents.
HELPFUL HINTS
Here is a list of "lucky 13" helpful guidelines for chemigation, from NCSU's Cooperative Extension:
1) Don't apply pesticides through an irrigation system if the soil is wet. (If one inch or more of irrigation or rainfall has occurred within the past 24 hours, the soil is probably too wet to apply pesticides.)
2) Use the least amount of water possible to apply the chemicals.
3) Don't chemigate when you mean to irrigate.
4) Use field borders to catch runoff water around the treated areas. Field borders planted in vegetation can be very useful in preventing runoff into surface waters.
5) Use erosion and runoff controls.
6) Use conservation tillage, terraces, strip-cropping, contouring, and/or sediment catch basins (or farm ponds) to reduce runoff. Close-growing crops such as grass or small grains are especially effective as cover strips to catch runoff and retain pesticides.
7) Avoid wind drift by considering weather and equipment.
8) Make certain that center-pivot, linear move, solid-set, or drip/trickle systems have the proper nozzle size and water pressure to provide large water droplets, which are resistant to wind drift.
9) Do not chemigate when wind speed exceeds 5 mph.
10) Do not use gun-type sprinklers that spray a fine mist high into the air.
11) Locate the irrigation equipment to cover the entire field, but do not place the sprinklers close to the field edge.
12) Apply only pesticides labeled for use in irrigation systems.
13) Regularly check equipment for:
· water leaks in the system
· proper operation of the antisiphon system
· proper setting and function of relief and check valves
· clogged nozzles
Because micro-irrigation systems apply water within or in close proximity to the rootzone of a crop, these systems are well suited for injection of fertilizers.
Selecting the appropriate filtration system for your irrigation system is an important decision. There
are screen filters, sand separators, disk filters, sand media filters, gravity screen filters and rotating suction screens
1) What is the water source? Is it well water or surface water? The primary contaminants found in well water are typically inorganic in nature such as sand, silt and clay particles. The primary contaminants found in surface water are typically organic in nature, such as algae and leaves. Many of the filters designed for well-water applications do not function well in surface-water environments. Likewise, many of the filters designed for surface-water applications do not function optimally in well-water applications.
2) What is the flow rate and the pressure of the system? This is critical information. Take for example the designed operating pressure of the system. Many microirrigation systems on the market today are designed to operate at very low pressures. This must be taken into account when filtration systems are being evaluated. Some filtration products operate with a very low pressure drop and some do not. Also, many of the automatic filters on the market today require a minimum pressure to accomplish their backflushing routine.
3) What is the water quality of the water source? Every filter application is usually vastly different from the next. One well on a grove may produce virtually no solids (sand, silt, etc.,) while another well on the same grove may pump a great deal of particulates. This may be caused by a number of factors such as well construction and well depth. Furthermore, the water quality of the water source may fluctuate over time.
Well-water quality fluctuates when the water tables fluctuate. Likewise, surface water quality can significantly change over the course of a year. These water-quality fluctuations must be anticipated. Shuster explains that there are some very accurate ways to measure the true solids loading of a particular
Well-water application. Miller-Leaman sends out a parts-per-million testing device to dealers. It estimates the amount of particles the well is pumping. based on the information, the appropriate filter is recommended.
4) What level of filtration does the application require? This is commonly referred to a mesh requirements or micron requirements. The filter mesh requirements for a specific application
are basically a function of two things. First, what emitters are being utilized in the irrigation system? Are they microsprinklers or drippers? What is the orifice size of the emitters? The dealer needs to communicate this information to the filter manufacturer. What is the size of the particles that need to
be filtered? Many wells pump a variety of particles ranging in size
from small rocks to fine silt particles. Dealers should be encouraged to
send particulate samples to determine the particle distribution that the
filter will be exposed to during normal operation. There are some simple
procedures that can be done to give this information. One common procedure
that we use is sieve analysis.
To help you begin your new lawn watering schedule, here is your personal sprinkler evaluation and scheduling guide. Call the RISE BBS for your local water use number. Look for it in "N -- NJ WISE". Pick your specific county. Choose the weather station located closest to your home. Option 3 "ET and energy" will give you your water requirements day-by-day (look under the Et column). If you live outside the 4 county area call for a guide you can use without depending on a weather station.
Irrigation system evaluation
1. Place three or more coffee-type cans (or rain gauges) at various locations on your lawn.
2. Turn on your sprinkler(s) for 30 minutes.
3. Measure water caught every 5 minutes in each can with a ruler (or measure the total amount and divide by 6 for 5 minute intervals); doing it that way, you won't get wet!
4. Record your sprinkler output measurements.
5. Call the RISE BBS and see how much water was used -- in your area -- yesterday. For odd/even schedules -- just add the last two days numbers together. Check your chart for the "depth" needed and how long to let the sprinkler run to replace the water your turf used.
6. Rainfall is not uniform over a large area. Keep track of it at your home. Rain gauges are under $5.00 and are available at your local garden center. Change your watering schedule to reflect the rainfall amount.
Depth caught every five minutes over a 30 minute time period
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