BASIC IRRIGATION OPERATION ACHIEVING AN EFFECTIVE AND EFFICIENT IRRIGATION Irrigation is both an art and a science. Research has provided many concepts and methods for measuring the various processes involved in irrigation. However, knowledge of the field and crop, along with the grower’s experience in interpreting this science, will remain of utmost importance in achieving effective, efficient irrigations. Effective irrigations produce the desired crop response DISTRIBUTION UNIFORMITY AND IRRIGATION EFFICIENCY There are two measures of irrigation performance – distribution uniformity and irrigation efficiency. Distribution Uniformity (DU) is a measure of how evenly water soaks into the ground across a field during the irrigation. If eight inches of water soaks into the ground in one part of the field and only four inches into another part of the field, that is poor distribution uniformity. Distribution uniformity is expressed as a percentage between 0 and 100%. Although 100% DU (the same amount of water soaking in throughout the field) is theoretically possible, it is virtually impossible to attain in actual practice. Efficient irrigations make the best use of available water Irrigation efficiency does no good if it is not effective in producing a profitable crop. Effective, efficient irrigation is a result of knowing when to irrigate, how much to irrigate, and how to irrigate. • When – an agronomic decision based on how you want to manipulate your crop. • How much – – depends on the soil moisture depletion in the effective root zone. This is the amount of water needed to take the soil moisture reservoir back to field capacity or other desired level. • How – this is not just about knowing how to set a siphon, or connect a sprinkler pump. It is also knowing how to apply water evenly to a field while controlling the total amount applied. An effective, efficient irrigation produces a profitable crop while making the best use of available water supplies and creating a minimal impact on water quality. In doing so it must also minimise energy use and save money. Irrigation Efficiency (IE) is the ratio of the volume of irrigation water which is beneficially used to the volume of irrigation water applied. Beneficial uses may include crop evapotranspiration, deep percolation needed for leaching for salt control, crop cooling, and as an aid in certain cultural operations. Differences in specific mathematical definitions of IE are due primarily to the physical boundaries of the measurement (a farm, an irrigation district, an irrigation project, or a watershed) and whether it is for an individual irrigation or an entire season. Irrigation efficiency is also expressed as a percentage between 0 and 100%. An IE of 100% is not theoretically attainable due to immediate evaporation losses during irrigations. However, it could easily be close to 95% IE if a crop is under-watered. In this case, assuming no deep percolation, all water applied and not immediately evaporated would be used by the crop. The term irrigation efficiency should not be confused with the term water use efficiency (WUE). WUE is generally a measure of yield per unit water applied. RELATIONSHIPS BETWEEN DU AND IE There are two important relationships between DU and IE: deep percolation and under-irrigation. The illustrations below show a profile view of two adjacent sprinklers in a field and the root zone under them. The horizontal, dashed line in the figures depicts the depth of the actual soil water depletion at irrigation.
Download PDF file
Cookie policy