Application efficiency is a term used to define the difference between the water taken from a water source and the water reaching a position where the target plants can use the water (usually at the plant roots). At this point the similarities between humid area irrigation and arid area irrigation diverge. If water does not reach the soil or remain in the soil where roots are during irrigation, it is lost, and this directly reduces the efficiency of the irrigation system. Of course, there are other uses for irrigation besides meeting crop needs (seed bed preparation, seed germination, transplant establishment, softening a soil crust during emergence, crop cooling, frost protection, salt removal, etc.; *Burt, et al., 1997). In this report the primary use of irrigation in our humid region is associated with consumptive use, the required by the plant to meet evapotranspiration requirements. All other uses are either tied to arid conditions or are usually minor components of overall irrigation applications in the southeast, and will not be extensively addressed in this report.

Travelling Gun In an irrigation system, losses may occur at any position in the water’s pathway. Application efficiencies are affected by system leaks, system water pressure (decreased droplet size), evaporation rate, wind speed and direction, uniformity of application, canopy interception, deep percolation, and other factors. Application efficiencies can vary widely by crop and type of irrigation system. For the most part, irrigation systems which expose water to the atmosphere for a long period of time are subject to decreased application efficiency. In the southeast, and particularly in Georgia, the majority of the irrigation systems being used are already the most efficient available for the particular crop and land conditions. Very little if any surface (including furrow, level basin, flood, ...) irrigation is used. Water table management (WTM, also known as sub-irrigation) is used extensively in North Carolina and Florida, but few systems have been installed in other states (*Shirmohammadi et al., 1992). Surface and WTM are usually less efficient irrigation alternatives. The predominate use of center pivot, drip/trickle, traveler, and solid set irrigation results in relatively high application efficiency potential. We say potential, because poor design and management of a particular system can result in poor application efficiency even though the average system is efficient.

In irrigation system design, application efficiency and uniformity are critical factors. Uniformity implies how consistently emitters/sprinklers apply water across the irrigated area. In most irrigation systems all the sprinklers or emitters do not apply the same amount of water. Those near a mainline tend to emit more water than those at the end of lines due to pressure losses. Sprinklers and emitters may not wear evenly and some variation exists in manufacturing. As a result, water application can vary significantly across a field. Obviously, a system with high uniformity is desirable to ensure the entire crop is receiving the same amount of water.

In many irrigation system evaluations, the characteristics of application efficiency are based on the output from the low quarter emitters. The definition of low quarter emitters or sprinklers is the 25% of the emitters or sprinklers discharging the least amount of water in the irrigation system. The following are considered "reasonable" application efficiencies from two different sources.

*Keller and Bliesner (1990) state: "Average application efficiencies are based on full crop canopies and systems that are well-designed and carefully maintained. The values are estimates and should be considered accordingly. Under conditions where poor management, poor design, or conditions are not suited for irrigation, values may be much lower ..."

Application Efficiencies of the Low Quarter Emitters/Sprinklers (*Allen, 1991)

System	Range (%)	Average
Sprinkler Solid Set Center Pivot Linear Move Big Gun Traveler Trickle	60-75 70-85 65-85 55-65 60-80 70-95	70 75 75 60 70

Other Efficiency Values: (*Keller and Bliesner, 1990)

Efficiency (%)
Moving or set systems with excellent uniformity in cool or humid climates and low winds. Moving systems in most climates and winds; and set systems with medium to high application rates and good uniformity. Average set system in most climates and winds. Travelers Gun or Boom sprinklers Periodic-move laterals Fixed lateral	85 80 75 70 60-75 70-85 70-88

In defining application efficiencies which correspond to crop type in Georgia, the predominate irrigation system used for crops such as corn, cotton, peanut, soybean, sorghum, and wheat is the center pivot system. For tobacco, the predominate system type is traveler. For peaches, the systems are split between drip/trickle and traveler. For pecan, the systems are split between drip/trickle and sprinkler. For vegetables, the predominate irrigation system used is drip/trickle. Watermelon and Vidalia onions, two of Georgia's largest acreage horticultural crops, are predominately under center pivot. In practically all cropping situations, a different type irrigation system than mentioned above is probably being used on some acreage. Therefore, recommendations for improvement need to be addressed for each individual system.

Source: Evans, R.O., K.A. Harrison, J.E. Hook, C.V. Privette, W.I. Segars, W.B. Smith, D.L. Thomas, and A.W. Tyson. 1998. Irrigation conservation practices appropriate for the Southeastern United States. D.L. Thomas (ed.) Geologic Survey Project Report No. 32. Georgia Geologic Survey, Georgia Department Of Natural Resources, Environmental Protection Division, Atlanta, GA 30334. 43p.