Excess water may also reduce crop yields below potential levels through mechanisms such as leaching of plant nutrients, increased disease incidence or failure to stimulate growth of commercially valuable parts of the plant. Irrigation uniformity is also linked to the efficiency with which agricultural resources are used. To the extent that non-uniformity causes crop yields to fall below potential levels, agricultural inputs applied in anticipation of full yields are wasted. Because irrigation uniformity relates to crop yield and the efficient use of resources, engineers regard it as an important factor to be considered in the selection, design and management of irrigation systems. Various measures of uniformity are used as indices of performance by which, for example, sprinklers and sprinkler spacings are judged.
Uniformity plays a similar role in decisions regarding other types of irrigation systems.
In surface irrigation design, limits on factors like flow rates or furrow length are set so that non-uniformity in the water application will not be excessive. Hydraulic limitations on pipe networks for trickle and sprinkler irrigation are similarly determined. There are many measures of irrigation uniformity in use, and a discussion of all of them is beyond the scope of this paper. Two commonly used measures will be presented here to facilitate comparisons in some later examples. 59 Christiansen developed UC to measure the uniformity of sprinkler systems, and it is most often applied in sprinkler irrigation situations.