Emergency Irrigation Considerations – July 2012
Scott Sanford (Extension Engineer)
With the extended dry weather and no rain in the forecast, growers are looking for alternatives to supply crops with water. Governor Walker has issued a drought emergency declaration for 42 counties in southern Wisconsin which allows growers to pump from state surface waters with a temporary permit from the DNR. (See link to news release in resource list below.) The question is what would it take to irrigate an acre or more of crops? There are four things that are needed to irrigate: water supply, method to transport the water to the field, method to distribute the water to the crops and it has to be economical.
Water
The water source, quantity and quality are all important. Irrigation water can come from a well, surface source or be food plant or manure effluent. The water quality affects the type of irrigation distribution system that can be used and sometimes the amount of water that can be applied. The limiting factor in most cases for emergency irrigation is the quantity of water required to have a positive outcome. To apply a one inch depth of water to an acre of land requires 27,154 gallons (acre-inch). The water requirement of crops (evapotranspiration – (ET)) in recent weeks has averaged about 0.25 inches per day to grow a productive crop without stress. Therefore, a grower will need sufficient capacity to supply 6,800 gallons of water per day per acre of irrigated land to keep up with plant transpiration and evaporation. If you are pumping from a well or a surface water source and can pump 24 hours per day, this equates to about a 5 gallon per minute flow rate. Growers that have limited water availability often try to water everything a little, but this usually ends with poor results. If the crop doesn’t receive enough water to improve the yield or crop quality, thus resulting in increased income, then the grower is better off doing nothing. Growers should only irrigate the number of acres for which they have an adequate supply of water to meet the plant ET use.
If you are irrigating a crop for direct human consumption and using a surface water source, it is recommend that you have the water tested for pathogens and contaminates. The Wisconsin State Lab of Hygiene or other water testing labs can supply that service.
Transporting water to the field
Water can be pump several miles but may require booster pumps along the pipeline to overcome friction losses and elevation changes. Pumping is the most efficient method for moving large quantities of water. If you don’t have water within pumping distance and are considering trucking water, a semi-tanker can hold 5,500 to 9,000 gallons of water so one tanker load would cover 0.8 to 1.3 acres of area to a water depth of 0.25 inches.
Water Distribution system
Sprinkler irrigation is typically used to distribute water to row crops. The most practical distribution systems for emergency irrigation are moveable pipe or traveling gun systems. The irrigation system has to match the pump / water supply capacity and pressure. Sprinkler nozzles are sized for a specific design flow rate and pressure in order to achieve uniform distribution of water and therefore must be matched to the proper size pumping system. The sprinkler nozzle must extend above the crop canopy for proper coverage. Moveable pipe irrigation must be set up with the lateral pipe and sprinkle spacing it was designed for to get uniform coverage. Typical spacing is 30, 40 or 60 feet between lateral pipes. A traveling gun systems reduces the amount of labor required and can cover an area of 50 to 300 foot wide and a length of up to 1700 feet depending on the system size, water system pressure and capacity per set. Water system requirements range from 5 to 700 gallons per minute at a pressure of 50 to 70 psi up to 160 psi. The higher the water system pressure, the greater the width of the coverage area. Sprinkle systems are best when using surface water sources or effluent or water with high amounts of dissolved minerals.
Drip Irrigation
One of the disadvantages of sprinkle irrigation is the amount of water that doesn’t get fully utilized by the crop, either because it is placed too far from the crop’s roots or losses due to evaporation or leaching. Drip irrigation places water at the roots and eliminates much of the evaporation, thus reducing the water volume by 30 to 50%. It also reduces weed control costs because no water is applied between rows and uses low water pressure, usually about 20 psi, resulting in lower energy costs. Drip irrigation requires clean water due to the small openings use to meter the water out and thus filtering is recommended. It is also higher in initial cost.
Refer to the Irrigation tool in the USDA Energy Self-Assessment tool at www.ruralenergy.wisc.edu for more information on other types of irrigation systems. Your Wisconsin irrigation equipment dealer can assist with the selection of equipment for your application and aid you with the design and layout of irrigation equipment.
Economics
This aspect is the hardest for many growers. What is the best option? Should I do anything? Irrigation is expensive to purchase and to operate so it is generally only used on high value crops. The payback on irrigation should be the difference between doing nothing and purchasing and operating irrigation for the “typical” year with 2012 being very a-typical. If you can’t recover the amortized cost of an irrigation system with increased yields or higher quality in the “average” year over a period of years, then it’s a poor investment and one should take the drought loss this year.
Resources:
Sprinkler Irrigation Systems, MWPS-30, Midwest Plan Service, Ames, IA, http://www.mwps.org/
DNR to expedite farmers’ water diversion requests due to drought emergency, Wisconsin DNR – http://dnr.wi.gov/news/breakingnews_lookup.asp?id=2421
Waterway & Wetland Permits: Withdrawals & Irrigation, Wisconsin DNR http://dnr.wi.gov/waterways/water_levels_crossings/irrigation.html
Drip Irrigation on-line references
Drip Irrigation Design Guidelines – http://www.irrigationtutorials.com/dripguide.htm
Drip Irrigation Planning Guide –
http://cdn.dripworks.com/downloads/manuals/DripPlanningGuide.pdf
Ro-Drip User Manual – Roberts Irrigation Products, Inc –
http://www.trickl-eez.com/rodrip.pdf
Wisconsin Agricultural Irrigation Dealers
Roberts Irrigation, Plover, WI – 715-344-4747 – http://www.robertsirrigation.net
North Central Irrigation, Beloit – 800-924-0321 and Plainfield, WI – 800-755-0268
http://www.valleynci.com/
Oasis Irrigation, Almond, WI – 715-366-8000 – http://oasisirrigationllc.com/index.htm
TIP, Inc, Custer, WI – 800-225-9727 – http://www.tipinc.net/index.html
There are also many drip irrigation equipment suppliers online.