Submitted to: Decennial National Irrigation Symposium
Publication Type: Proceedings
Publication Acceptance Date: November 14, 2000
Publication Date: N/A
Interpretive Summary: LEPA is the most efficient sprinkler method available to growers with as much as 95 to 98% of the sprinkler water available for crop use. During recent years, considerable research has been conducted to optimize the LEPA sprinkler method for on-farm use. A review of LEPA research, during the past decade to include equipment development and recommendations for specific crops, has been prepared for the Fourth Decennial National Irrigation Symposium. The review showed that the LEPA bubble and LEPA double-ended sock have become the preferred LEPA methods, that runoff due to high application rates has the largest detrimental effect on LEPA irrigation efficiency, and that surface storage from basin and reservoir tillage are preferred for preventing the runoff. With full irrigation, maximum crop yields and the resulting water use efficiencies are similar to those for other highly efficient irrigation methods such as the spray sprinkler method and subsurface drip irrigation. With deficit irrigation for less than maximum crop yields, the runoff potential decreases, and LEPA irrigation tends to be more efficient than spray irrigation for drought tolerant row crops such as cotton and grain sorghum. Although the LEPA sprinkler method is not used extensively on-farm, spray sprinkler heads are now used with narrower spacings and placed within the crop canopy to approach the high LEPA application efficiency.
Technical Abstract: Advances in LEPA irrigation during the 1990s were primarily in equipment development, surface storage measurement, runoff control, and guidelines for LEPA irrigation of specific crops. LEPA application efficiencies in the 95 to 98% range are attainable when surface runoff and deep percolation are negligible. Uniformity coefficients along the irrigation system mainline can exceed 0.95 and, in the direction of travel, can exceed 0.80 with furrow dikes spaced about 2.0 m apart. Surface runoff has the largest detrimental effect on LEPA application efficiency and uniformity. Without tillage to control runoff, runoff fractions exceeding 50% of the LEPA irrigation have been measured. The two primary methods for controlling runoff are basin and implanted reservoir tillage. With alternate furrow irrigation, they provide surface storage depths on a field basis of 25 mm or more and 12 mm or more, respectively. Bubblers and socks or sleeves have ebecome the two most commonly used LEPA application devices. Bubblers are available in multi-function application devices that also include flat spray and chemigation modes. Single-ended and double-ended socks are usually attached to a spray application device for controlling the discharge rate. LEPA irrigation guidelines have been developed for corn, cotton, grain sorghum, wheat, and some minor crops. With full irrigation, crop yields and water use efficiencies are similar to those of other highly efficient irrigation methods such as spray and subsurface drip. With deficit irrigation, the runoff potential decreases, and LEPA tends to be more efficient than spray for drought tolerant row crops such as cotton and grain sorghum.