1. Got Water? Developed by:
This lesson is the third in the Soil and Irrigation Module. It relates soil characteristics to water-holding capacity. An overview of irrigation methods is included.
Developed by:
Hud Minshew, Oregon State University Extension Service
Susan Donaldson, University of Nevada Cooperative Extension
UNCE, Reno, Nev.

2. Today we’ll learn about
Sources of irrigation water: surface versus well water
Matching available water to soils and plants
Determining when it’s time to irrigate
Irrigation systems
Instructor: Review the agenda with your students. Be sure to adapt the “Irrigation Systems” section to reflect practices in your area.

3. Where will you get your water?
Do you have a water right?
Where will your water come from?
When or how often will you get your water?
Even though you may have an irrigation ditch running through your property, this does not mean you have the right to use the water! Before you irrigate, you’ll need to know if you have a water right attached to your property. This means that you have a legal right to use a supply of water on your property for irrigation purposes. Usually the water right comes with the title of the land when purchased. Check to see if you have a water right, and how much water is involved. If you do not have a water right, you may find it difficult and/or expensive to obtain one.
In addition to checking on your legal water right, you’ll want to consider how and when your water is delivered. Is it from a ditch or canal? A well? A stream? These are all important questions. For example, if you receive water from a ditch, you might experience limitations, including when or how often you can irrigate. In several states, lateral ditches are regulated by neighborhoods, and sometimes it can become a contentious issue to determine who gets water and when.
Instructor: Each state will differ in this respect. Contact your state’s water resources board to obtain information on water rights and uses.

4. So you think you’ll use your domestic well to irrigate a pasture?
Does local law allow use of domestic well water for pasture irrigation?
Does your well produce enough water?
In many western states, the use of domestic well water may be limited to indoor and landscaping use. There may also be limits on the amount of water that can be used on a daily basis from domestic wells. For example, in Nevada, domestic well owners are limited to using 1,800 gallons/day from their wells. In Oregon, the limit is 15,000 gallons/day. This is quite a large amount of water, ranging from 50,000 gallons to 450,000 gallons per month. For purposes of comparison, one acre-foot contains 326,000 gallons. Because most wells do not have meters, it can be difficult to determine how much water you’re actually using.
Even if you are legally permitted to use your domestic well for irrigation purposes, unless the well supplies water at a reasonable rate, you may find it inadequate for your purposes. Generally speaking, simply for household use, wells should supply a minimum of 10 gallons per minute. A much higher level of production will be needed if the water is to be used for irrigation purposes.
UNCE, Reno, Nev.

5. Things to know before you start to irrigate
What plants do you want to grow?
Do you have enough available water to support the plants?
Are your soils appropriate for growing the plants you selected?
Once you’ve established that you do have the right to use water, you can start contemplating the many factors that go into planning an irrigation system. To start with, what type of soils do you have? Have you consulted your soil survey or appropriate agency to determine the suitability of your land to grow crops? What kind of crops do you want to grow? How much money and time do you have? An irrigation expert can help you answer some of these questions. Check with your local irrigation distributors, university extension, and the Natural Resources Conservation Service (NRCS) for advice.
To meet the requirements of a crop, you have to have sufficient water to meet the peak demand of that crop. Local information on crop demands can be obtained from your university extension or from the NRCS office. Your system capacity is dependent upon peak evapotranspiration rates, available water-holding capacity of the soil, and the efficiency of the irrigation system. Your soil survey data will provide information on the water-holding capacity of the soil.
UNCE, Reno, Nev.

6. More things to know before you start to irrigate
Do you want to improve existing pasture, or start over?
How much time and money do you have?
Renovation refers to starting over and replanting a pasture. Reasons to renovate include poor yields, severe perennial weed problems, or the desire to redo an irrigation system. Renovation can either be partial or total. Renovation is covered in detail in Module 5, Lesson 4.
Partial Renovation:
Improves productivity and forage quality with minimal yield loss during establishment.
Minimizes soil erosion.
Total Renovation:
Replaces all of the existing forage..
Enables you to plant a better, more productive forage.
Increases the possibility of erosion until vegetation is well-established.
Requires more labor and costs more than partial renovation.
Other factors to be considered when choosing an irrigation system include the shape and size of your field, and the topography. Slope steepness will determine whether a surface or sprinkler system will be used. If you broadcast seed on a slope and then flood irrigate, most of the seed will wash away. Sprinkler irrigation may be needed until grass roots become established.
USDA Online Photos

7. Where do plants get their water from in the root zone?
When considering which plants to grow, remember that most moisture is extracted by the plant roots present in the upper half of the rooting zone. In this idealized graphic, 40 percent of extraction occurs in the top one-quarter of the root zone, 30 percent in the next quarter, and only 30 percent in the lower half of the rooting zone. The upper rooting zone is the area where the soil will tend to dry out fastest, and where most nutrients are extracted. It’s important to manage irrigation water to keep it within the effective rooting zone. Water that moves below this root zone becomes unavailable to the crop, is effectively “wasted,” and can leach nutrients into groundwater.
Every plant is different in its rooting habits, of course, and restrictive soil layers may affect rooting depths.
Photo source: Adapted by A. Miller, Black Dog Graphics, from Soil Water Monitoring and Measurement. PNW 475. A Pacific Northwest Publication. Washington, Oregon and Idaho. Thomas Ley et al.
Adapted from PNW 475 by A. Miller

8. Plant rooting depths vary
Alfalfa
4’ – 6+’
Rooting Depth in Feet
Plant rooting depths vary
An irrigation schedule also needs to take into account the rooting depth of the plants. This slide shows a range of rooting depths for a variety of crops when the soil has no restriction to the growth of roots. When irrigating, try to manage irrigation water to keep it in the effective root zone (the zone with the majority of roots) and not beyond. In salty soils, however, it may be necessary to overapply irrigation water to leach salts out of the root zone.
Instructor: Ask participants how plants would be affected if their soil had a limitation at the 2-foot depth, such as a high water table, clay layer, or bedrock.
A. Miller

9. Before you pick a crop, consider the soil
What is the capability class of the soil?
What are the slopes and aspects?
How deep is the soil?
Does it have adequate drainage and rooting depths?
Is compaction an issue?
If you participated in the first two lessons of this module, these are all familiar terms, and you can answer these questions.
Capability classes were established by the U.S. Department of Agriculture to classify a particular soil or soil map unit in a soil survey. They show the potential or suitability of a soil for growing crops. Soil surveys have other information that you will find useful when planning your crop.
Slopes and aspects govern sunlight hours, temperatures and suitability of certain irrigation systems. For example, applying water by flooding a severe slope is not an effective method, as the water may run off faster than it can soak in.
If your soil has less than a 10-inch effective depth, it is generally not suitable for an irrigated crop, as it will be difficult to impossible to maintain sufficient soil moisture. It may be possible to irrigate shallow soils effectively with drip irrigation, if water is applied often enough.
Compaction is an issue that relates to construction equipment and animal traffic, both of which have the potential to severely compact soils and decrease available air- and water-holding capacity.
Instructor: For more information on capability classes, see Module 2, Lesson 2.
USDA NRCS

10. Composition of a loam soil
Water = 20 to 30%
Air = 20 to 30%
Mineral
Fraction
(sand, silt,
clay) = 45 to 50%
Organic Matter = 0 to 5%
In Lesson 1, you learned that a typical “loam” soil is composed of about 45 to 50 percent pore space. This pore space volume can be as little as 30 percent in a sandy soil and as much as 50 percent in clay soils. Pore space determines the amount of water potentially available to plants.
Instructor: Ask the students, “Which weighs more, a bucket of dry sand, or a bucket of dry clay?” The answer is sand, due to its increased density (mass per unit volume). However, students will usually guess clay, opening the door for fruitful discussion.

11. Soil texture How does it feel in your hand? .
NRCS, Bozeman, Mont. .
Soil texture
The texture of a given soil tells you a lot about how you will need to manage your irrigation system. Coarse-textured or sandy soils have much higher intake rates than clayey soils, as well as lower water-holding capacity. Clay soils are prone to high runoff because of their low infiltration rates.
What does that mean? In general, sandy soils absorb water readily (higher intake), but the water drains out easily (lower water-holding capacity). Clay soils absorb water slowly (lower infiltration rates), but they hold the water once it has infiltrated (higher water-holding capacity). Knowing the texture of your soil can help you develop the most efficient and effective irrigation system and irrigation schedule for your soil.
If you also know the degree of aggregation (clumping) of the soil, you’ll also be able to predict something about infiltration rates. Highly aggregated soils with high water-holding capacity often have rapid infiltration rates.

12. Water spreads differently in different soil textures
Deepest penetration
Moderate spread and infiltration
Wide, but more shallow, infiltration 
CLAY
SILT
SAND
Water spreads differently in different soil textures
Water infiltrates differently in soils with different textures. Water spreads more widely in a clay soil because of higher water tension compared to sandy soils. You’ll also note that the depth to which the soil has wetted is greater in the sandy soil due to lower water-holding capacity.
In soil with 50 percent available water content, if you apply an inch of water, in a sandy soil the water will move downward 40 inches; in a fine sandy loam, 24 inches; and in a loam soil, only 12 inches.
This slide also provides a good demonstration of what can occur when a drip system is used. The placement of the drip line relative to the plant is an important consideration, especially in sandy soils.

13. Soil texture and drainage
A. Miller
Soil texture
Infiltration rate,
inches per hour
Sand
2 - 4
Sandy loam
1 - 3
Silt loam, loams
0.25 – 1.5
Silty clay loams, clay
0.1 – 0.3
Different soil types transmit water differently. Sandy soils allow water to infiltrate rapidly, but water also drains easily from the large pores. Infiltration rates for clay soils can be quite slow, and the runoff potential is high. But, the water holding-capacity is large due to the finer pore space.

14. Plant-available water is the part of the water stored in the soil that can be absorbed sufficiently by plant roots to sustain life. When the soil is holding as much water as it can after it has been completely wetted and allowed to drain freely, we call this the field capacity of the soil. The wilting point of the soil occurs when the free water has been used up, and the remaining water is so tightly held that plants cannot use it to meet their transpiration needs. Notice that as the soil texture becomes finer (more clayey), the soil can hold more water, but it also will not release water as readily as a sandy soil. The graph shows that loamy soils have the best ability to store and release water to plants.
Instructor: Use the Sponge-and-bucket Soil Water-holding Demonstration from the lesson plan to show how water is held in soils.
Available water
OSU Extension Service

15. Available water
This diagram depicts what is happening on the microscale in soil as it drains. In the graphic at the left, notice all of the pores are filled at saturation. At field capacity, a percentage of the soil pores contain water. The biggest pores empty first, followed by smaller pores. In the graphic on the right, the soil is at wilting point, but notice there is still a small amount of water in the smallest pores and along the soil surface. This water is held tightly on the soil surface and in the cracks between the soil particles, and is not available to the plants.
A. Miller

16. The water available to you
Does your water right supply enough water?
Will you have water during dry years?
Do you need to reduce your irrigated acreage to match your water supply?
Can you use your water more efficiently?
There are a number of other considerations to review before you determine what and how you’ll irrigate. Often the limiting factor on the plant species and amount of acreage that you’ll irrigate is the size of your water right. For example, in Nevada, it takes about 4 1/2 acre-feet of water to irrigate an acre of alfalfa through the growing season. Suppose you only have 2 acre-feet of water available to you? You might choose to irrigate less acreage or to plant a crop that requires less water.
Many water rights exist on paper only. Water rights are also time dependent. The oldest water rights granted get the water first. If the water supply in a given year is inadequate, only users with the oldest water rights will receive their irrigation water.
How often do droughts occur in your area? Do you have alternative water sources, or will you need to let your pasture go dormant?
Instructor: Use a local example.
UNCE, Reno, Nev.

17. When is it time to irrigate?
Rule of thumb: when the amount of water-holding capacity is at 50% – but that’s hard to tell!
If your plants are showing signs of stress, irrigation is overdue
Look for wilting or grasses that don’t spring back up when stepped on
The most accurate way to determine how much and how often to irrigate is to calculate your irrigation needs using a combination of soils information (water-holding capacity) taken from soil-water-monitoring equipment, evapotranspiration data and irrigation efficiency data. For most small-acreage owners, this information may not be readily available.
Whenever possible, avoid letting the soil dry out to the point where plants are stressed. You can monitor for stress by looking for wilting, color changes or lack of resilience. When you walk across a lawn that is stressed, your footprints will remain visible for some time because the grasses are too dry and unable to spring back up. The same effect can be seen in pastures.

18. The Look-and-feel Method
Probably the simplest soil-moisture testing method a landowner can use is the look-and-feel method. Using a shovel, dig down to the root zone of the crop and pick up a handful of soil. Alternatively, to avoid disturbing the soil excessively, use a soil sampler or a drill bit.
Generally, if the soil holds together and does not fall apart, there is adequate moisture. This technique, however, varies depending on the soil type, as shown in the following two slides.
Many fact sheets are available on this method from your extension office or NRCS.
USDA NRCS

19. Look-and-feel method
Clay, clay loam or silty clay loam at 25 to 50% moisture
Clay, clay loam or silty clay loam at 50 to 75% moisture
Learn to judge moisture by squeezing a handful of soil. Clayey soils will react as follows.
Soil on the left: Slightly moist, forms a weak ball, very few soil aggregations break away, no water stains, clods flatten with applied pressure.
Soil on the right: Moist, forms a smooth ball with defined finger marks, light soil/water staining on fingers, ribbons between thumb and forefinger.
Irrigation should occur at 50 percent moisture, as highlighted in red on the slide.
Instructor: Distribute the Determining Irrigation By The Look-and-feel Method Activity Sheet and provide soils of differing textures at varying moisture contents for participants to use when learning this method.
Photos, guides and soil-moisture descriptions for four soil types are provided courtesy of Estimating Soil Moisture by Feel and Appearance, USDA Natural Resources Conservation Service.
See for more information or handouts.
Irrigation is overdue.
Will need to irrigate soon.
USDA NRCS

20. Look-and-feel method
Sandy loam or fine sandy loam at 50 to 75% moisture
Sandy loam or fine sandy loam at
25 to 50% moisture
Irrigation is overdue.
Will need to irrigate soon.
Sandy soils will resemble those described below.
Soil on the left: Slightly moist, forms a weak ball with defined finger marks, darkened color, no water staining on fingers, grains break away.
Soil at the right: Moist, forms a ball with defined finger marks, very light soil/water staining on fingers, darkened color, will not stick.
Irrigation should occur at 50 percent moisture, as highlighted in red on the slide.
Photos, guides and soil-moisture descriptions for four soil types are provided courtesy of Estimating Soil Moisture by Feel and Appearance, USDA Natural Resources Conservation Service.
See

21. Screwdriver method
This method is also very easy to use. Take your longest screwdriver or a piece of rebar at least 12 inches long. A ¼-inch steel rod with a “T” handle works particularly well. Push it into the soil. If the soil is wet enough, you should be able to push it in all the way. If you encounter resistance midway, the soil may be too dry. If you suspect you have hit a rock, try another spot. This method only provides information on the moisture content of the upper 10 to 12 inches of soil.
UNCE, Reno, Nev.

22. Using evapotranspiration data to schedule irrigation
In some locations, information on the actual daily use of water by plants (evapotranspiration) may be available from weather stations, such as this one. Scientists can use measurements of wind speed, temperatures, humidity and precipitation to calculate plant water use and provide accurate estimations of the amount of water that should be applied on a given date.
Once you know the flow rate of your irrigation system, convert it from gallons per minute or gallons per hour to inches of water applied over a given period of time over a given area. Go to for a simple conversion tool. You can then estimate the amount of water to be applied according to the average inches of evaporation reported.
Instructor: Insert any information on local or state ET programs here.
For more information on Washoe County Nevada ET Program, see
Or, see for the Pacific Northwest Cooperative Agricultural Weather Network.
Bureau of Reclamation

23. Irrigation water quality
Does your irrigation water contain trace elements that may affect plant growth?
Is the water salty?
What are upstream users doing that might affect your water quality?
Nearly all waters contain dissolved salts and trace elements, many of which result from the natural weathering of the earth's surface. Drainage waters from irrigated fields can also impact water quality. In most farming situations, the primary concern is salinity levels, since salts can affect both the soil structure and crop yield. However, a number of trace elements, such as boron, are found in water and can limit its use for irrigation. Most salinity problems in agriculture result directly from the salts carried in the irrigation water.
If a glass of salt water is left in the sun, as the water evaporates, the dissolved salts remain, resulting in a solution with a higher concentration of salt. The same process happens in soils. Salts, as well as other dissolved substances, begin to accumulate as water evaporates from the surface and as crops withdraw water.
When in doubt, get your irrigation water tested. Several parameters are used to define irrigation water quality, to assess salinity hazards, and to determine appropriate management strategies. A complete water quality analysis will include determination of:
the total concentration of soluble salts,
the relative proportion of sodium to the other cations (positively charges ions),
the bicarbonate concentration as related to the concentration of calcium and
magnesium, and
the concentrations of specific elements and compounds.
The amounts and combinations of these substances tell us the suitability of water for irrigation and the potential for plant toxicity.
Instructor: If possible, evaporate samples of local irrigation water in a clean glass vessel and show students the residue.

24. Salt-affected soils
Any mention of irrigation must include the problem of salt accumulation in soils. Soil salinity affects cropping systems worldwide and is especially significant in arid regions with poorly drained soils. Salts originate from mineral weathering; inorganic fertilizers; soil amendments such as compost, manure, or gypsum; and irrigation waters. Road salts and ice melters are other sources of salts.
Soils impacted by salts are called either saline or sodic. Saline soils are high in soluble salts. As salinity levels increase, it is more difficult for plants to extract water from the soil, aggravating water stress conditions. High soil salinity (salt-affected soils) can also cause nutrient imbalances, result in accumulation of elements toxic to plants, and reduce infiltration.
Other soils are called sodic, and they are high in exchangeable sodium. These soils are hard and cloddy when dry, and tend to crust. Water intake is usually poor, especially in soils high in silt and clay, and pH tends to be high, often above 9.
Soils are classified as salt-affected based on electrical conductivity (EC) and exchangeable sodium, reported as the Sodium Adsorption Ratio (SAR). Generally speaking, crop yields are not significantly affected where the electrical conductivity is 0 decisiemens to 2 decisiemens per meter (dS/m). Many crops are restricted at levels of 4 dS/m and higher. An SAR value below 13 is desirable.
USDA-NRCS

25. Irrigation methods: selecting the system that’s right for you
Surface
Most often, small-acreage owners will use the method of irrigation that was in use on their property when they bought it, or the method most people in the neighborhood use. There are many methods, however, and often the choice of a different method may result in improved efficiency, more even application or a saving in labor.
Before selecting a system, you’ll need to consider:
proximity of the field or pasture to a water source
adequate distribution system to the field (pumps, canals or pipes)
amount of water required by selected crop
quality of available water
cost of water
topography of the land
soil type
annual precipitation
cost of irrigation supplies
availability of labor to install and maintain the irrigation system
fertilization methods
methods for recycling or handling excess irrigation water
Irrigation systems vary in sophistication and cost to install, and each system has its advantages and disadvantages. We’ll cover some of the more common systems that you might choose to use on your property.
Sprinkle
USDA NRCS
Micro-irrigation

26. Are you using an existing system, or starting over?
Your flexibility may be limited with an existing system, but costs will be lower
Starting over allows you to carefully match soils, plants and water availability with irrigation systems, but can be costly
New irrigation systems may save time, money or water
When starting over, be sure to take advantage of the opportunity to carefully match your irrigation system to your resources. This may include leveling of fields or new irrigation infrastructure. Don’t forget to include cost of installing and maintaining the system, and labor involved in operating the system.
Instructor: Your students will be interested in the costs of various systems. Costs vary by area, year, and system. The handout, Comparing Irrigation Systems, provides an estimate of costs from “minimal” to “very high.” Current information is available from your state NRCS Web site. For Montana, the address is Substitute your state’s abbreviation for “mt” in the address to get to your state NRCS Web site. Then click on Electronic Field Office Technical Guide (eFOTG), Section I, Cost Data, and “Cost of Applying Conservation Practices.” Not all states have cost data for irrigation systems. The Utah and Montana Web sites provide detailed information.

27. What source of power will you use?
None – select an irrigation system that does not require power
Electricity from an existing power line
An internal combustion engine
Solar power
When available, electricity is the most commonly used source of power because it is the least expensive. In situations where an existing power line is not available, this may affect your decision regarding irrigation systems. The cost of construction and extension of power lines vary by electrical provider, so call your power company for estimates. Also consider the annual cost of electricity to power the system when making decisions.

28. Surface irrigation (gravity-flow)
UNCE, Reno, Nev.
The practice of surface or flood irrigation is thousands of years old, and is very little changed today. The water is distributed to a corner of each pasture through a network of small ditches and gates, with water flowing down slope by the pull of gravity. In the United States in 2000, about 29.4 million acres were irrigated by flood irrigation, as compared to about 28.3 million acres irrigated by sprinkler irrigation. About 50 percent of systems use furrows. Border/basin and uncontrolled flood application systems account for the remaining acreage. Gravity-flow systems are used in all irrigated areas, and are particularly predominant in the arid West. But remember – surface water in open channels moves only in the downslope direction!
Advantages of flood irrigation include low input and maintenance costs for equipment, and the ability to irrigate without an external power source. Disadvantages include low irrigation efficiency rates, increased labor and poor uniformity if the field is not properly leveled, which can be expensive! Water losses are comparatively high under traditional gravity-flow systems due to percolation losses below the root zone and water runoff at the end of the field. Field application efficiencies typically range from 40 to 65 percent, although improved systems, such as surge irrigation, may achieve efficiencies of up to 85 percent with proper management.
FAQ: Surface Irrigation Systems
NRCS Irrigation Page
UNCE, Reno, Nev.

29. Wild-flood irrigation
If the water is allowed to flow unimpeded over the land surface without the use of furrows, borders or other structures, it is called wild-flood irrigation. Wild-flood is the cheapest but least efficient method of irrigation. It is extremely labor intensive, as the property owner must walk through pastures with a shovel and readjust flow patterns with virtually every irrigation cycle to ensure the water is distributed to all parts of a field.
UNCE, Reno, Nev.

30. Contour-ditch irrigation
Contour-ditch irrigation is a form of controlled surface flooding. Ditches running across the slope, approximately on the contour, distribute the irrigation water to the field through temporary dams. The dams cause the water level in the ditches to rise, and the water then spills out through openings in the bank, or over a uniformly graded lower bank of the ditch. The water then flows down the slope from one contour ditch to the next, and the runoff is collected in the lower ditch for reuse.
Univ. of Virgin Islands

31. Field leveling
Field leveling involves grading and earth-moving to eliminate variations in the gradient by smoothing the field surface and often reducing the slope. Field leveling helps to control the advance of water and improve uniformity of soil saturation under gravity-flow systems. Precision leveling is generally undertaken with a laser-guided system.
Different types of surface irrigation require different slopes. Border irrigation requires a 0.2 to 0.4 percent slope. Furrow irrigation requires a 0.5 to 3 percent slope.
USDA NRCS

32. Level- basin irrigation
Level-basin (or dead-level) systems differ from other border systems in that field slope is level and field ends are closed. Water is applied at high volumes to quickly and evenly fill the basin. The floor of the basin may be flat, ridged or shaped into beds, depending on crop and cultural practices. Basins need not be rectangular or straight-sided, and the border dikes may or may not be permanent. Basins can vary in size from very small to as large as 40+ acres.
Surface runoff can be eliminated by this method, but precision-laser leveling is generally needed to prepare fields for this method. Level basins simplify water management, since the irrigator need only supply a known amount of water to the field. High efficiencies of up to about 80 percent are possible with low labor requirements.
USDA NRCS

33. Corrugation
Corrugation is a surface irrigation method where small channels or indentations are used to guide the water across a field. The corrugations run down the slope and help convey the water, rather than contain it. Some overflow is expected. Corrugations are often used in pastures.
UNCE, Reno, Nev.
CSU Cooperative Extension

34. Furrow irrigation (level and graded)
Furrows are channels formed in the soil. They are larger than corrugations, and are intended to completely contain the irrigation water. Water soaks in and spreads laterally in the furrows, and crops are planted in the raised soils between furrows. Systems may be designed with a variety of shapes and furrow spacings, including level and graded systems. The water infiltration rates in the furrows may be quite variable, even when soils are uniform, due to cultural practices such as compaction.
These systems require infrastructure including dams, canals, valves and drainage systems; are often inefficient (30 to 50 percent); and require a lot of effort to maintain. If a tailwater recovery system is installed on these systems, the efficiencies can be increased by 25 percent.
USDA NRCS
USDA NRCS

35. Contour-furrow irrigation
This method is similar to the graded furrow system, but is used to irrigate sloping fields by carrying the water across, rather than down, the slope. The furrows are curved to fit the land surface, and have just enough downslope to carry the irrigation water. Head ditches or pipelines run downhill or slightly across the slope to feed individual furrows. The system is less costly than land leveling for border irrigation, and works reasonably well if the furrows are spaced correctly for the soil type.
Icrisat.org

36. Furrow irrigation with siphon tubes
USDA NRCS
In furrow irrigation, water can be delivered to individual furrows through cuts in the head ditch. Alternatively, curved aluminum or plastic siphon tubes can be used as a means of delivering water directly to each furrow. Water flows into the submerged end of the tube, is siphoned over the bank of the open ditch, and then is delivered into the furrow. This method has the advantages of preserving ditch integrity and providing almost identical flows to each furrow. The siphon tubes do require maintenance to remove trash and floating debris that may clog the tubes.
Excavated earthen ditches are prone to leakage and require regular maintenance and dredging to maintain flows and manage weeds. However, the leakage may supplement shallow groundwater recharge, and plant growth can provide wildlife habitat. Concrete-lined ditches minimize leakage and maintenance requirements, and have fewer problems with weeds, but provide poor wildlife habitat.
USDA NRCS

37. Components of a border irrigation system
Border irrigation is used to irrigate strips of land that are level across the narrow dimension, but slope along the long dimension. The strips are bounded by ridges or borders. Water is turned into the upper end of the border strip, and advances down the strip. High irrigation efficiencies (80 to 90 percent) are possible with this method of irrigation, but are rarely obtained in practice, due to the difficulty of balancing the water application.
On steeply sloping lands, the ridges are more closely spaced and may be curved to follow the land contour.
Border systems are suited to orchards and vineyards, and close-growing field crops such as alfalfa, pasture and small grains.
USDA NRCS
A. Miller

38. Gated pipe
UNCE, Reno, Nev.
Gated pipe can be used with flood irrigation systems to improve control over water delivery. Water from a lateral ditch or a well is diverted through a screen into the gated pipe. The irrigator then opens or closes individual gates (often spaced about 18 inches apart) to control where water is applied, and for what length of time. The initial costs may be high, and the screen must be cleaned regularly. Once in place, however, gated pipe allows you to customize the water delivery to the variations in the pasture, and can help save water.
USDA ERS
USDA NRCS
NRCS Irrigation Page

39. Surge irrigation Water delivery is controlled by a valve.
Surge flow is an adaptation of gated pipe systems in which water is delivered to the furrow in timed releases that are controlled by a valve. The valves automatically alternate the water from one set of furrows or border strips to another. Deep percolation at the upper end of the field is reduced, and water penetration at the lower end is increased, resulting in more even water distribution. Also, runoff can be decreased by careful management of valve settings. Many of these systems incorporate battery, solar-powered controllers.
ERS USDA

40. Alfalfa valves
Alfalfa valves or risers are designed for use in surface irrigation systems to provide effective shut-off and regulation of flow from underground pipelines to irrigation furrows or checks. Alfalfa valves are also used with portable hydrants and gated pipe in row-crop irrigation.
Univ. of Idaho Extension

41. Bubbler screen
Bubbler screens (also known as turbulent fountain screens) are used with gravity systems to help reduce contamination by weed seeds. The water passes through a screen and into a gated pipe. The weed seeds are left in the top of the screen. To avoid clogging, the screen must be cleaned periodically. Bubblers are particularly useful for organic growers seeking ways to reduce weed problems. NRCS may provide cost-share for these systems.
B. Hamblen, CSU Extension

42. Reducing return flows
Return flows consist of the water that flows off your property after irrigation. This occurs when the rate of water application is higher than the rate at which soil can absorb the water. Many irrigation ditches mix ditch water with waters from streams and rivers or may return water to the streams after use. By flooding efficiently and reducing return flows, you can reduce water pollution, including sediment, nutrients and pesticides.
This photograph shows an irrigation ditch intercepting a stream. There is no separation between the two, resulting in complete mixing of the water. This is a stream inhabited by trout and winter steelhead, where good water quality is essential to the fishery.
Whenever possible, time the application of irrigation water to minimize runoff. On slopes, consider using an alternate form of irrigation. During the time irrigation water is allotted to you, if you have areas that continually experience runoff, consider putting in a small tailwater pond to collect the runoff. You can then use the water to sprinkle irrigate in between flood cycles.
If you are at the bottom end of a ditch, keep in mind that your irrigation water may carry excess plant nutrients, including nitrogen and phosphorus. You may be able to take advantage of the nutrients and reduce your fertilizer rates below the recommended rates of application, while still producing an adequate crop or pasture.
USDA NRCS
OSU Extension Service

43. Reusing tailwater Do you have a legal right to reuse tailwater?
How will you capture and store the water for subsequent use?
Maximizes the use of surface irrigation water.
Tailwater is the water that flows off the lower end of a field when the irrigation rate exceeds the ability of the soil to infiltrate the water. Most surface systems produce some degree of runoff or tailwater.
Reuse systems collect and return the runoff for use in subsequent irrigations. In some locations, this may not be a legal use of the water, so first check your local water laws and regulations. Then, you need a method to capture and store the water. Some landowners use a pond located at the most downslope portion of the property. Water is then pumped from the pond to another location for future irrigation. These ponds should be empty once the irrigation season has ended. Other systems may incorporate the use of a large water tank.
Reuse of tailwater adds flexibility to irrigation scheduling and can increase the effectiveness of irrigation by 25 to 30 percent. However, you must have a location to collect the tailwater, and your pumping system must be maintained. Also, there may be safety issues associated with open ponds.

44. Ditch maintenance Dredging and redigging Weed and vegetation control
Opening and closing of gates
Adjusting of siphon tubes
Who will do it, and what will it cost?
Permission and access issues
OSU Extension Service
Irrigation ditches require regular maintenance to improve water delivery. If they become overgrown with willows or other vegetation, velocities will be reduced, and water may not be delivered in a timely fashion. A vegetated ditch bank helps avoid erosion. However, combating weeds and maintaining a vegetated bank can be very difficult. In some states, regular spring burning is used to control weeds and grasses in ditches.
In some areas, a ditch company will collect fees from all irrigation water rights holders on that ditch. They then hire “ditchriders” to maintain the ditches and operate the main gates.

45. Powered systems: sprinklers
Sprinkler irrigation, which includes moveable hand lines, side-roll wheel lines, solid set and center-pivot systems, has an efficiency that ranges from 60 to 75 percent and can require a high initial investment. The efficiency of sprinklers varies dramatically according to the method of operation.
Pressurized sprinkler systems generally use less water than gravity flow (flood irrigation), but much of the spray in the air, as well as the water falling on plant leaves, evaporates on hot, dry days. Short irrigation cycles in the heat of the day that prevent water from soaking deep into soil can result in as much as 80 percent of the water being lost by evaporation. For this reason, sprinkling in the early morning hours when winds and temperatures are low will be most efficient.
However, when irrigation is conducted properly, sprinklers can not only be very efficient but can also solve the problems of local water distribution, such as getting water into the root zone. If the irrigation duration is too short, the losses from wetting the foliage and soil crust will be a high percentage of the water applied. An irrigation duration lasting too long will result in the water passing the root zone and being lost.
Because of wind scatter, placement of water is not exact and different areas of the pasture or lawn may receive different amounts of water. The “can test” can be used to determine if the system is delivering water evenly.
This type of irrigation system requires less labor and more equipment than gravity-flow methods, but it is the only practical way to irrigate uneven ground. It also allows timed delivery of water so that the infiltration capacity of the soil is not exceeded and runoff does not occur.
UNCE, Reno, Nev.

46. Center-pivot
Center-pivot sprinklers are a commonly used pressure technology in production agriculture. A center-pivot sprinkler is a self-propelled system in which a single pipeline supported by a row of mobile A-frame towers is suspended 6 to 12 feet above the field. Water is pumped into the pipe at the center of the field as towers rotate slowly around the pivot point, irrigating a large circular area. These systems generate the round “crop circles” that can be seen from the air.
Sprinkler nozzles mounted on or suspended from the pipeline distribute water under pressure as the pipeline rotates. The nozzles are graduated, small to large, so that the faster moving outer circle receives the same amount of water as the slower moving inside.
Typical center-pivot sprinklers are one-quarter mile long and irrigate 128- to 132-acre circular fields. Center-pivots have proven to be very flexible and can accommodate a variety of crops, soils and topography with minimal modification. However, the cost of the system plus the energy to operate it may be prohibitive for small-acreage properties.
USDA NRCS

47. Mini-pivot sprinklers
Mini-pivot sprinklers are shorter versions of center-pivot systems, and may suit small-acreage owners well. These systems have lower energy needs and can be solar-powered. They are less expensive than full-size pivots and better suited to smaller fields of up to about 60 acres. The water application is relatively uniform, and labor inputs are low once the systems are installed. However, the cost of the system may be too high to justify use for very small acreages.
USDA NRCS Mont.

48. Low-energy precision-application sprinklers
Improved center-pivots have been developed that reduce both water application losses and energy requirements . Older center-pivots, with the sprinklers attached directly to the pipe, operate at relatively high pressure (60 to 80 psi), with wide water-spray patterns. Newer center-pivots usually locate the sprinklers on tubes below the pipe and operate at lower pressures (15 to 45 psi). Many existing center-pivots have been retrofitted with system innovations to reduce losses and energy needs.
Low-energy precision-application (LEPA) is an adaptation of center-pivot (or lateral-move) systems that uses drop tubes extending down from the pipeline to apply water at low pressure below the plant canopy, usually on the ground or only a few inches above the ground. Applying the water close to the ground cuts water loss from evaporation and wind and increases application uniformity. On fine-textured soils with slower infiltration rates, furrow dikes may be necessary to avoid runoff.
USDA NRCS
USGS

49. Traveling guns (big gun)
Traveling-gun systems use a large, high-capacity sprinkler mounted on a wheeled cart or trailer, and fed by a flexible rubber hose. The machine may be self-propelled while applying water, traveling in a lane guided by a cable. Other systems may require successive moves to travel through the field. Big guns require high operating pressures, with 100 pounds per square inch (psi) not uncommon.
One of the major benefits of the traveling-gun system is that it can be installed quite rapidly. After the traveler has been set up, aluminum (or buried PVC) pipe is installed between the pump and the traveler. The major drawback of the traveling- gun system is that it is quite labor-intensive. Only movable, solid-set irrigation systems require more hands-on labor to move and set up than the traveling-gun system. Other drawbacks include the relatively high cost per irrigated acre of the system (when compared to some drip systems) due to power costs, and the low application efficiency of the system.
The big gun sprays a huge stream of water high in the air during irrigation, which is very susceptible to wind and evaporation losses, up to 30 percent or more in most cases. Still, traveling-gun systems are the method of choice for many small irrigation systems with oblong or odd-shaped fields.
The flexibility and portability of the traveling gun make it the only real solution in some instances. Irrigating smaller acreages (10 to 30 acres) is generally cost-prohibitive with a center pivot, so if drip irrigation is not an option for the crop in question, then the traveling gun may become the best irrigation method.
USDA NRCS

50. Traveling mini-guns
With a traveling mini-gun, water is supplied to a traveler via a connection from a buried PVC mainline with riser valves or an aboveground portable mainline. The traveler has either a soft hose or medium density polyethylene tubing. The polyethylene tubing is desirable because it keeps its shape and is flexible enough to be wound around a reel.
This system is suitable for well-drained soils that have high infiltration rates. Installation costs can be high, and costs to run the pumps are also high because of the extra pressure required to overcome friction loss due to the soft-walled tubing. Advantages include uniform watering, ability to water irregularly shaped areas, self-containment, and ease of working around obstacles.
See for more information on Bauer products.
USDA NRCS

51. K-line® and Irripod® sprinklers
Photo source?
The K-line® Irrigation System was developed in New Zealand and is now available in the United States. A similar system is marketed under the brand name Irripod®. The system consists of a series of plastic pods, each one containing a sprinkler head, that are spaced along polyethylene tubing. The pods/sprinklers are positioned throughout the pasture or hayfield and moved at intervals with an ATV (all terrain vehicle). Depending on the design, 12-hour or 24-hour set times are used and are capable of providing 1 to 3 inches of precipitation per week. The system has few moving parts (pumps and sprinklerheads) and is easily expanded and maintained. The low sprinkler height results in less wind drift, and the low-pressure system reduces operational costs. It is useful when irrigating irregularly shaped areas.
These systems are useful for irrigating pastures, but don’t work as well for row crops and tall-growing crops.                     
See for more information.
kygraziers.com

52. Hand lines
A hand line is a portable sprinkler system in which lightweight pipeline sections are moved by hand for successive irrigation sets of 40 to 60 feet. Lateral pipelines are connected to a mainline, which may be portable or buried.
Hand-move systems are often used for small, irregular fields. Portable hand lines are often used with row crops. They are not suited to tall-growing field crops due to difficulty in repositioning the lateral pipelines.
While hand lines have a low initial cost, the labor requirements are higher than for all other sprinklers, as the system must be moved and repositioned for each irrigation cycle. Also, the pipes are soft and easily damaged by livestock or equipment, making this a less desirable method for irrigating pastures.
ERS USDA
USDA NRCS

53. Side roll wheel lines
USDA NRCS
Wheel-line or side-roll systems are similar to hand lines that have been raised off the ground. They are designed to irrigate large, rectangular areas. A gasoline engine located in the middle of the line drives the line across the field. Large wheels are placed next to the engine and at the end of the line.
The advantage of the system is the ability to move an entire lateral at once. Maintenance is similar to hand lines, except for maintenance of the mover.
The initial cost is higher than hand line because of the thick tubing and extra components, but may be offset by the reduced labor. This system requires rectangular fields free of obstructions, such as trees or poles. Wheel lines can be troublesome on steep slopes and wet soils.
Crop type is an important consideration for this system since the pipeline is roughly 3 feet above the ground.
USDA NRCS

54. Solid-set sprinkler
UNCE, Reno, Nev.
Solid set refers to a stationary, permanently installed sprinkler system. Water-supply pipelines are often installed below the soil surface, and sprinkler nozzles are elevated above the surface. In some cases, hand-move systems may be installed prior to the crop season and removed after harvest, effectively serving as solid set. This system is simple to operate, as the sprinklers only need to be cycled on and off.
Solid-set systems are commonly used in orchards and vineyards for frost protection and crop cooling. Solid-set systems are also widely used on turf and in landscaping. When used in pastures, the sprinkler nozzles must be protected from livestock or equipment damage.

55. Below-ground popups
Below-ground popup sprinklers are sometimes used in horse pastures where permanent installation is desirable. Disking and other renovation practices may damage buried pipes, depending on their depth. The horses learn and avoid the locations of the sprinklerheads. Concrete rings, as shown in the photo, may also be used to protect the sprinklerheads. Some damage is inevitable, and solid-set sprinklers, as shown in the previous slide, may be preferable.
Avoid using popups in pastures with sheep and goats, as their smaller feet could slip down between the sprinklerhead and the donut, resulting in damage to both the livestock and the system.
Univ. of Idaho Extension

56. Drip irrigation
Drip-irrigation systems are systems that apply irrigation water slowly, under low pressure and in precise locations. Drip irrigation applies the water through small emitters to the soil surface, usually at or near the plant to be irrigated. These systems are designed to reduce the waste of water from evaporation. Drip irrigation can be applied on or below the surface of the ground. Initial costs can be high, but rewards include reduced weeds, less time and labor, reduced runoff and pollution, and lower pumping costs because of low volume. These systems are often not economical for use in pasture settings, but are best suited for tree or row crops, and can be used in oddly shaped fields.
Drip systems should have a backflow-prevention device (not shown in this photo) if connected to a drinking-water source. Other necessary parts of the system include a filter, pressure regulator and air/vacuum release valves.
More advanced systems have a chemical tank, a secondary filter and a flow meter. In these systems, chemical or organic fertilizer can be added directly in-line. This type of system is called chemigation. The most common drip systems include 1) emitters with tubing, 2) in-line tubing and pressure compensating emitters, 3) sweat tubing or porous hose and 4) low-volume sprinklers or misters.
Graphic by A Miller, adapted from USDA-SCS 1984
USDA SCS

57. Drip irrigation
USDA NRCS
Drip irrigation has become very popular, but there are some limitations that can result from the narrow distribution of water. This restricts root expansion and increases salinity levels at the edges of the wetted zone.
Notice that the only visible wet area in this drip irrigation system is at the very end of the drip line. This shows the precision of drip irrigation and the reduced loss of water through evaporation. However, with drip systems, especially subsurface systems, care must be taken not to overapply water, which can leach nutrients to the groundwater. Having a soil moisture monitoring system is therefore very important.
USDA ARS

58. Subsurface drip irrigation
UNCE, Reno, Nev.
Subsurface drip irrigation (SDI) is a variation of drip irrigation in which the pipelines, which include built-in emitters, are buried in the ground at the root zone. In the photos above, the lines have been photographed prior to burial and crop installation. Permanent driplines require thicker walls to withstand higher operating pressures, and the system must be carefully designed to suit soil texture.
Very little water is wasted by this method, as the water is deposited directly in the root zone. It is potentially the most efficient irrigation method available today, depending on proper design, installation and management, with efficiencies about 95 percent or higher. Because the soil surface stays dry, there is virtually no irrigation water lost to evaporation or runoff, and weed problems are minimized. On the other hand, if surface soil moisture is too low, it may be impossible to germinate shallowly planted seeds.
However, the initial cost of installation is expensive, and once installed, the system cannot be easily changed. One of the main problems with SDI is emitter clogging by mineral deposits, such as calcium carbonate. Test your water prior to designing and installing a subsurface irrigation system. Plant root intrusion may also plug emitters. Rodents may create leaks by chewing on the pipes.

59. Activity
Create a table showing the pros and cons of each of the irrigation systems discussed.
Instructor: Give participants a few minutes to brainstorm the pros and cons of the irrigation methods or systems discussed and then pass out the Comparing Irrigation Systems Handout and the Pros and Cons of Irrigation Systems Activity Sheet.

60. Checking your system: Does it apply water uniformly?
Uniformity of water application is a measure of how evenly irrigation water is applied or infiltrated throughout a field. Some systems have a higher uniformity than others, but all systems will apply more water in some parts of a field than in others.
Worn nozzles or poor design can result in problems with uniformity in sprinkler systems. Likewise, variations in topography will affect the water uniformity on surface-irrigated pastures. These are just a couple of examples of causes of non-uniformity.
When a field is not watered uniformly, differences in plant growth can result. One part of a field might be waterlogged and another part droughty. Both of these situations will stress a crop or pasture.
In this slide, there is more water sitting on the grass in the foreground than in the background. Wet soils will promote the growth of plant species such as wiregrass (rushes) that are not desirable forage plants. The pasture should not be grazing during irrigation. This picture shows what not to do!
UNCE, Reno, Nev.

61. Improving uniformity
Monitor your system during irrigation and check for leaks or clogging of screens
Look for areas that remain too wet or too dry and adjust your irrigation system
Check sprinkler system pressures and nozzles to make sure they are adequate
Consider system upgrades
For the average small-acreage owner with a flood-irrigated pasture, improving uniformity involves spending time during irrigation seeing where water is ponding, or where water is failing to reach the pasture grasses. At the simplest level, a shovel can be used to create furrows to drain or irrigate these areas. If your pasture irrigation is very uneven, you may want to consider switching to a different irrigation system, such as sprinklers, or leveling the pasture during renovation.
Renovation is done when pastures are no longer productive, and involves steps such as tillage, seed mix selection, planting and irrigation system upgrades. Take advantage of this opportunity to consider a system that improves water delivery, decreases runoff and water losses, and perhaps decreases the labor involved during the growing season.
Instructor: Renovation is covered in Module 5, Lesson 4.

62. The can method for measuring uniformity – a low-cost approach
The can method is particularly useful for sprinkler systems but won’t work with flood irrigation systems. It allows you to determine the inches of water you are applying, on average, to the lawn or pasture. It also allows you to determine which areas are receiving too much water, and which areas may be overly dry so that you can adjust your system to become more uniform.
Instructor: Distribute the Using the Can Method For Determining Sprinkler Output and the Sprinkler Distribution Uniformity Activity Sheets. Using several cans of water, show participants how to measure and calculate the average water delivered and the distribution uniformity. Point out that they can complete both tests with one trial, if desired, by first determining uniformity, and then calculating the average amount of water applied.
Ask participants to try the method prior to the next class and report back on how it worked. If available, provide participants with average water usage by month based on evapotranspiration (ET). Your state or region may have an ET Web site.
OSU Extension Service

63. Irrigation systems summary
Know your sources of irrigation water
Know your soil type
Monitor soil moisture
Improve efficiency of your delivery system when possible
This lesson provides an overview of irrigation systems. Before renovating or installing an irrigation system, it is wise to consult with an expert. The Natural Resources Conservation System or your local Cooperative Extension office can help you.
It’s essential to consider your goals in irrigating your property. Do you want a verdant green landscape or optimal forage production? Do you prefer minimal maintenance? Then consider what resources you have available: soil, plants, water, time and money. Choose a system that is best for you, considering your resources and limitations.

64. Irrigation systems summary
Adjust rate of water application to avoid runoff
Know your labor availability
Match your goals for your land to the irrigation system you select
Learn as much as you can about your irrigation system. You’ll want to understand how it works and what you can do to make water delivery as efficient and even as possible. This involves monitoring both the system itself and the level of soil moisture. You can then adjust the rate of water application to meet the needs of the crop without creating runoff, soil erosion, or other water quality problems.

65. Homework Practice the Look-and-feel Method for determining irrigation.
Inventory your irrigation system, both existing and proposed, using the Irrigation Checklist for Landowners Activity Sheet.
Check the uniformity of your sprinkler system, using any of the methods discussed in this lesson.              
Instructor: Customize homework to meet the needs of your students. Consider assigning a task of designing three alternative irrigation systems for use on each student’s property. Students should list pros and cons of each system, research estimated costs, and determine which will best meet their needs. Students who have flood irrigation should complete the Flood Irrigation System Checklist Activity Sheet.