Ag Alert May 21, 2025

IRRIGATION NEWS

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Increase your bottom line with good irrigation

By Charles Burt A farmer’s irrigation-related financial bottom line depends on costs and the quantity and quality of the harvested crop. Investment in a proper irrigation system and good maintenance and operation can certainly boost revenue. In California, it is common to have some under-irrigation on fields. If that is the case, there may not be any potential for water savings. However, the production from the scarce water can be increased with a better irrigation system distribution uniformity that minimizes the dry areas, thereby in- creasing yield and quality. This simultane- ously minimizes deep percolation of water and nitrates in areas that receive too much water. Think about highs and lows, or uni- formity of yield and water throughout the fields, in addition to average yields. View Google Earth images, which often show irrigation nonuniformity problems. Field sprinkler problems • To improve irrigation uniformity, check field sprinklers for common prob- lems such as short sprinkler risers. It’s amazing how often I see expensive water blasting into plants. • Typical 2.5 to 3.2 gallons-per-min- ute sprinklers should have about 55 pounds per square inch at the sprinkler to achieve good pattern overlap—not 55 psi at the pump. • If sprinkler pressures are too low, other solutions include the following: Increase the RPM of diesel engines; run fewer sprin- klers at once and decrease the sprinkler nozzle size. Be sure a smaller nozzle does not decrease sprinkler overlap pattern and realize this will decrease the application rate. You might consider installing a slightly larger pump, which may improve your bot- tom line by improving crop yield and quali- ty because of better distribution uniformity. • Sprinkler lines might be spaced too far apart. This results in poor overlap patterns. Remember that a closer spacing will apply more water per hour. • A field might have two or three noz- zle sizes. • Non-drain valves under individual sprinklers may solve one problem and cause another. Non-drain sprinkler valves close when the pressure drops to 10 or 15 psi. But some of these valves always have a 10-15 psi loss through them causing constant low sprinkler pressures. Drip or microsystem • Pressures are sometimes too variable or low throughout a field. Check pressures throughout the field. Purchase a 0-30 psi pressure gauge and a pitot tube. Punch a hole in the drip hose or tape and insert the pitot tube to take measurements. Then, plug the hole with a Goof Plug when fin- ished. Be sure to check pressures while water is flowing. • Systems without pressure compensa- tion (non-PC) emitters should have less than 20% pressure difference between emitters within a field, not just down a single hose or tape. Check the pressures at

efficiencies and look at your power bill to get a good idea of how much you can spend to improve pump efficiency. • Vertical turbine pumps have options to consider, including using new line shaft bearing materials such as vesconite for product (water)-lubed pumps. There are new line shaft bearing oiler designs that maintain a constant drip rate regardless of how full the oil take is, and impeller ma- terials such as aluminum bronze are more resistant to sand wear than other materials. Variable frequency drives • A pump with a Variable Frequency Drive (VFD) must be selected to oper- ate efficiently for all conditions. Ask your pump dealer to provide a graph showing the performance of a new pump with a VFD on your system and expect a clear explanation. • Ask whether the VFD, wiring and motor conform with standards au- thored by me and others at the California Polytechnic State University, San Luis Obispo, Irrigation Training and Research Center at www.itrc.org/VFD. Focus on quality, and work with an ex- cellent irrigation dealer who understands total irrigation system design rather than focusing on a few components. Most growers emphasize how much a system will cost as opposed to examining equal- ly important aspects of quality, options, long-term maintenance and operation costs, expected life and so on. To learn more, download the “Irrigation Consumer Bill of Rights” endorsed by The Irrigation Association and used by good irrigation dealers at www.itrc.org/reports/icbr.htm. Charles Burt is professor emeritus of irrigation and founder of the Irrigation Training and Research Center at California Polytechnic State University, San Luis Obispo. He can be reached at charlesmburt@gmail.com.

A grain field in Kings County shows sprinkler risers are too short, causing nonuniform irrigation. To evaluate whether irrigation hoses are flushed frequently enough, growers can use a nylon sock, inset, which in this case shows contaminants left in the system.

• Open the media (sand) tanks and make sure there is enough media inside. • Open the ends of the last hoses or tapes during irrigation and let the water flow into a nylon sock to see what is caught. • Cut apart plugged emitters to ex- pose the flow paths and see what causes the plugging. Big root zones are good • Tree crops tend to do better with a big, wetted root zone. Two drip hoses per row are intended to help. • Drive down the road and see how many fields have two drip hoses sitting right on top of each other. Pumping purchases • Efficiency is important. The average electric pumping plant (motor and pump) efficiency in California is less than 50%. An improved efficiency of 65% would save about 25% of your present energy bill if you pump the same amount of water with the new pump. Check your present pump

the beginning and ends of hoses through- out the field. • Check the loss across hose screen washers by measuring the pressure in the hose with the hose screen washer in place, and then with a standard wash- er in place. Some growers discard hose screen washers because they cause so much nonuniformity. • Make sure PC emitters have enough pressure. Some will work fine as long as they have more than 6 psi. Some PC mi- crosprinklers need about 25 psi before the PC function engages. • Check the pressure at the beginning of the first hose after each block pressure regulator. All regulators should deliver the same pressure. Emitters can plug, learn why • The filter backflush water should be discharged through a big, short pipe. Otherwise, it will restrict the backflush flow rate, and your filter will just get dirtier over time.

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