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<br />~ <br />C) <br />'f") <br />o <br />:::J <br />.~ 33 and 36 had some deep percolation but less than in 1990. A field <br />test of sprinkler application rates at these sites indicated that <br />the inflow meters were underestimating the amount of flow to the <br />sprinklers. Adjustment of data showed water application to be <br />higher than previously estimated and this resulted in showing <br />larger deep percolation than before. <br /> <br />The actual deep percolation seems to be considerably higher than <br />the 15% of ETa targeted. A target of 15% deep percolation is used <br />as being practical and achievable. However, until several years of <br />data are collected, it will be difficult to determine the amount of <br />deep percolation required to leach salts just below the root zone <br />and to prevent excess percolated water from carrying more salts to <br />the Colorado River. Currently, high deep percolation leaches salt <br />past the root zone to the Colorado River. <br /> <br />Application Efficiency: Application efficiency is calculated as <br />inflow minus outflow minus the deep percolation divided by inflow, <br />expressed as a percentage. As a result, when there is under- <br />irrigation, the application efficiency will be very high and may <br />not necessarily be an indication of good irrigation. The seasonal <br />application for all sites (surface and sprinkler) is provided in <br />Table 2. The table shows application efficiency to be 43% for <br />surface irrigation sites (20 sites) and 67% for sprinklers (3 <br />sites). When annual and perennial crops are taken into account, <br />the efficiency is 36% and 49% respectively. Application efficiency <br />for individual irrigation events are shown under site summaries in <br />Appendix B. <br /> <br />The overall seasonal irrigation application efficiency in 1991 was <br />45% which is less than 1988 and 1989 (Table 4). This is <br />considerably better than 1985, which had an efficiency of 30%. A <br />comparison of irrigation monitoring data from 1985 to 1989 shows <br />that during this period irrigation efficiency increased <br />progressively from year to year which resulted in less water <br />application, reduced runoff and deep percolation (Table 4). <br /> <br />Of the 20 surface irrigated sites monitored in 1991, only six had <br />irrigation efficiency 50% or more, considerably less than 1989 and <br />1988 where half the sites had more than 50% efficiency. Eight <br />producers increased their efficiency in 1991 compared to 1990 but <br />an equal number reduced their efficiency in 1991 compared to 1990. <br />This could be due to crop change (corn to alfalfa at site 43/44 and <br />small grain to alfalfa at site 46). site 47 had an operator <br />change. <br /> <br />In 1991 the variation in efficiencies for individual irrigations <br />ranged from 22% to 82% for surface irrigation and from 35% to about <br />90% for sprinklers (refer to Appendix D for more details on <br /> <br />19 <br />