Posted 25 April 2012. Forage and Grazinglands.
Water Source, Soil Moisture All Considerations for Assembling Forage Irrigation System
Source: University of Arkansas Press Release. www.uaex.edu
Stuttgart, Arkansas (April 20, 2012)--Chris Henry, assistant professor-irrigation, and Dirk Philipp, assistant professor-forages, both of the University of Arkansas System Division of Agriculture, offer specifics that producers should take into account if a forage irrigation system is under consideration:
“The equipment needed depends on the long-term business plan,” Henry said, adding that for forages, “linear move systems, traveling guns, center pivots and K-Line systems can be used.”
The K-Line system, which is relatively new to North America, consists of heavy-duty sprinkler pods strung along polyethylene tubing that can be moved by ATV or small tractor.
“No irrigation system is like any other and each will have to be ‘custom-built’ to meet the specific conditions of the farm,” Henry said. “Design of the irrigation system requires input from an irrigation specialist. It’s an investment that will pay for itself in the long term.”
Those interested in developing an irrigation system should seek assistance from their Natural Resource Conservation field office.
Pump sizing and type is critical -- each is designed for a specific purpose, he added. Proper planning of an irrigation system is critical so that it meets the needs of a producer and the crop that is being irrigated. For example, the K-Line works well for irrigated grass, but is not suitable for irrigated corn, where a center pivot could be used for either.
Philipp also said hay irrigation needs differ depending on whether the producer is growing hay or grazing beef or dairy cattle.
Finding a reliable water source is the first step to developing an irrigation system.
“What would yields be from well water?” Can water be drawn from a river?” Henry asked. “If so, annual use must be reported to the Arkansas Natural Resources Commission.
“Everything comes down to soil moisture monitoring to keep soil moisture at optimum levels,” Philipp said. Too little water and plants get stressed. Too much water and “air is pushed out of the pores and limits root growth.
“Over-irrigating is as detrimental to crop growth as under-irrigating,” Henry said. “It’s a common misconception that because I have an irrigation system, I have to use it all season long at to its full capacity.
“Irrigating is about supplementing rainfall, providing just what the plants need,” he said. “Too much, and it is lost to deep percolation and can inhibit production.”
Henry said irrigation systems are designed to provide adequate water at peak evapotranspiration rates, “which is only experienced just before plant maturity.”
“Application depths must be managed during the season to provide just enough irrigation to supplement rainfall,” he said. “Using an irrigation system at full capacity during the growing season wastes water and costs money.”
“How much irrigation is needed and when do I need to irrigate? For irrigating pastures, hay and forages, a good rule of thumb is to put on two inches of irrigation down right after cutting or intense grazing,” Henry said. “The grass will respond to this irrigation. An atometer ET gauge, can be used to measure evapotranspiration” to check water use. They provide the same ET data as that from a weather station, but are easier to use.
And because land plants take up water from the soil, knowing the of the plants’ root zone is imperative.
“Sensors can be installed at different depths to infer water movement in soils and along the root zone, allowing the producer to differentiate between crop water use and drainage,” Philipp said.
Sensors should be placed to monitor three depths. “With just one sensor, it’s difficult to tell if water is being used by crops or being lost to drainage, or both,” he said.
Producers should use sensor data as their trigger point to initiate irrigation. Both the sensor and ET gauge only cost a few hundred dollars, but more importantly, they help to plan ahead. If the plants look stressed, then irrigation is too late.
“Irrigation scheduling is critical for success and is based on soil water monitoring or with tools that measure evaporation,” Philipp said. “In conjunction with assessing the condition of the crop, irrigating based on soil water monitoring is a safe method of providing crops with the correct amount of water needed.”