Selecting an Irrigation System Ronald F. Gronwald Water Management Engineer USDA NRCS Greensboro, NC
An Irrigation System is more than the Application Method • Source of water • Management of water • Conveyance of water • Application of water • Capture and reuse (Tailwater Recovery)
Field Source 1 2 1 3 7 1 Pressure flow to field 2 Sprinkler application 3 Runoff 4 Capture 5,6,7 Return flow Tailwater Pond 4 6 5
Irrigation Systems • Surface Irrigation • Subsurface Irrigation • Sprinkler Irrigation • Microirrigation
Surface Irrigation Water applied by gravity flow • Basin Irrigation – Entire field is flooded • Furrow Irrigation – Water fed into small channels • Border Irrigation – Strips of land divided by low dikes are flooded sequentially
Suitable crops • rice (grows best when its roots are submerged • pastures, e.g. alfalfa, clover • trees, e.g. citrus, bananas • Crops which are broadcast, such as cereals (Basin and Border Irrigation) • Row crops (Furrow Irrigation) • Not suited to crops which cannot stand in wet or waterlogged conditions for periods longer than 24 hours. (root and tuber crops) • Potatoes • Beets and carrots (require loose, well-drained soils)
Suitable soils and land slope • Flatter land surfaces are best suited to surface irrigation methods • Loamy soils are best (to avoid permanent saturation of the soil) • Sands are not recommended for surface irrigation as, due to the high infiltration rate, percolation losses can be high.
Water requirements • A high volume, intermittent flow rate is required
Advantages of Surface Irrigation • It is the simplest of all irrigation systems • Low initial cost • Low energy costs if gravity can be used to supply the water • Works well in odd shaped fields
Disadvantages of Surface Irrigation • High maintenance requirements • Inefficient in water use • Nutrients and pesticides are lost by deep percolation below the root zone • Is not suitable for crops which grow below ground such as potatoes, peanuts, sugar beets and carrots.
Subsurface Irrigation • Irrigation water is applied below the ground surface, thus raising the water table to the crop root zone
Suitable Crops • Most crops are well suited for subsurface irrigation except very deep rooted crops such as alfalfa and cotton.
Suitable Slopes Works best on flat fields
Suitable Soils • The best suited soils have an impermeable layer 5 or more feet below the surface • Water is supplied to the roots by upward capillary action (upflux). Medium textured soils are best. (Fine sandy loams)
Advantages of Subsurface Irrigation • Permits storage of water in the lower soil profile • Reduces pumping costs • Can be incorporated into an existing drainage system with low additional cost • Captures plant nutrients at or near the water table for future use by plants
Disadvantages of Subsurface Irrigation • Labor intensive to adjust elevation of weirs to change from drainage mode to irrigation mode and back again after heavy rains • System cost can be high in soils with low hydraulic conductivity or rolling topography • Water quality must be high
Sprinkler Irrigation • Water is applied similarly to natural rainfall • Pumps supply water under pressure • Water is distributed through a system of pipes to sprinkler heads • Water breaks up into small water drops which fall to the ground • Must be designed and operated to ensure a uniform application of water
Types of Sprinkler Systems • Hand Move or Wheel Line • Big Gun • Solid Set • Center Pivot • Linear Move • LEPA (Low Energy Precision Application) • LESA (Low Elevation Spray Application) • LPIC (Low Pressure IN Canopy) • MESA (Mid Elevation Spray Application) • Variable Rate
Suitable crops • Row crops • Field crops • Tree crops • Big Gun not recommended for irrigation of delicate crops such as lettuce that may be damaged by large drops.
Suitable slopes • Adaptable to any farmable slope, uniform or undulating • Best when operated parallel to the land contour (to minimize pressure changes along the lines)
Suitable soils • Best suited to sandy soils with high infiltration rates • Adaptable to most soils if runoff is avoided • Not suitable for soils which easily form a crust (use fine sprays to avoid crusting)
Water requirements • The best water sources for a sprinkler system are a wells and ponds. • Low volumes but a continuous supply is needed
Advantages of Travelers (Big Gun) • Low initial cost • Very mobile - can be used in multiple fields • Works well in odd shaped fields • Can be used to apply manure or lagoon effluent
Disadvantages of Travelers • Requires high operating pressure • Uses more energy than other systems • Requires a grassed travel lane • Delivers large droplets which may damage some plants or damage soil surface • Has high instantaneous delivery rate
Advantages of Hand Move Systems • Low initial cost • Works well in odd shaped fields
Disadvantages of Hand Move Systems • High labor costs • Must be moved from once to 3 times a day • Difficult to use on large fields or with tall crops such as corn
Advantages of Wheel Line Systems • Low initial cost • Works well in level fields that are square or rectangular • Can be used in trapezoidal shaped fields by adding or removing pipe sections from one or both ends • Lower labor cost than hand move systems
Disadvantages of Wheel Line Systems • Can only be used on low growing crops • Difficult to move in the direction parallel to the pipe • Rolling topography makes alignment difficult
Advantages of Solid Set Systems • Can irrigate entire fields at once • Can be used for multiple purposes • Irrigation • Frost protection • Crop cooling • Chemical applications
Disadvantages of Solid Set Systems • High cost • Risers and sprinkler heads may be damaged by equipment during the growing season
Advantages of Center Pivots • Easy to use • Low labor costs • One system can irrigate a large field • When used with corner attachment, can irrigate almost any size and shape field • Adaptable to many different soils, variable terrain and management objectives.
Disadvantages of Center Pivots • High initial cost • Has variable application rates across the system (highest at the outer portion of the system. • Requires a complex control system • Vulnerable to lightning and ice damage • Typically requires three-phase power supply
Advantages of Linear-move Systems • Easy to use • Low labor costs • One system can irrigate more than one field • Water is applied uniformly across the length of the system • Water intake can be from a ditch or from a drag hose.
Disadvantages of Linear-move Systems • High initial cost • Best suited to rectangular fields with a length to width ratio of at least 2:1 • It is not well adapted to fields with rolling terrain