Author
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Schneider, Arland |
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Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 4/28/2000 Publication Date: N/A Citation: N/A Interpretive Summary: Sprinkler irrigation designers, suppliers and users, face considerable uncertainty about the relative on-farm efficiency of the LEPA (Low Energy Precision Application) and spray sprinkler irrigation methods. As much as 98% of the water applied with the LEPA method has been reported as beneficially used while comparable efficiencies for the spray method have been about 85%. The LEPA method, however, requires more expensive equipment and more intensive management, and the high intensity application rates can cause water to runoff the irrigated fields. Are LEPA irrigation efficiencies actually that much higher than those of the spray method, and is the additional cost and management time to obtain the higher efficiencies justified? An in-depth literature review showed that the efficiency and uniformity of application of the LEPA and spray sprinkler methods are similar enough that neither method can be considered inherently ysuperior to the other. Selection of the best method requires careful evaluation of the types of evaporation losses by the two methods, the crops and cropping systems and the management options and costs. This synthesis of information from various sources provides guidelines for irrigation designers and supplies, extension personnel and growers searching for the "best" sprinkler method for a center pivot. They can select the best equipment, sometimes at lower cost, and eliminate unnecessary management time and still use their irrigation water efficiently. The results have widespread application since the two sprinkler methods are used on tens of thousands of center pivot irrigation systems both in the USA and internationally. Technical Abstract: Application efficiencies and uniformity coefficients reported for the LEPA (Low Energy Precision Application) and spray sprinkler irrigation methods are summarized and interpreted for improved system design. Application efficiency for LEPA typically exceeds 95% with surface runoff eliminated, but is reported as low as 80% with runoff. Spray application efficiencies calculated from collector measurements are considerably less than those based on measurements such as chemical tracers, weighing lysimeter catches and energy balance modeling. Because of unknown amounts of evaporation from collectors and reduced catches due to wind, spray application efficiencies reported for the other measurements that exceed 90% are believed to be more accurate. With the small droplet evaporation losses reported for spray irrigation, net canopy evaporation reported in the 3 to 6% range becomes a significant portion of the spray water loss. Because of fthe start and stop nature of mechanical move irrigation systems, uniformit coefficients for LEPA and spray are measured both along the pipeline and in the direction of travel. For LEPA uniformity coefficients along the pipeline commonly exceed 0.95, but coefficients less than 0.5 have been measured with collectors along the direction of travel. With 3 to 4-m spaced furrow dikes to average the application over several system moves, LEPA uniformity coefficients in the direction of travel can exceed 0.80. Uniformity coefficients for spray irrigation are generally in the 0.75 to 0.85 range both along the system pipeline and in the direction of travel. The intense instantaneous application rates of both LEPA and spray, make surface storage from basin or reservoir tillage necessary for LEPA and desirable for spray. |
