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<br />CJ <br />r..::;J <br />~V')l <br />~ <br /> <br />:7:-' <br /> <br />PART 1 <br /> <br />:,:.::~ <br /> <br />IRRIGATION MONITORING AND EVALUATION <br /> <br />FINDINGS AND RECOMMENDATIONS <br /> <br />These findings are based upon the results of 6 years of irrigation <br />monitoring conducted in the Grand Valley by the Soi I Conservation <br />Service from 1984 to 1990. The findings are presented as a management <br />tool to accompl ish some of the sal inity control objectives stated in <br />page 4. <br /> <br />1. Overuse of water is prevalent throughout the Grand Valley <br />because of abundant supply of inexpensive irrigation water. <br />Most producers are not concerned about irrigation water <br />management (IWM). Very few farmers practice a high degree of <br />IWM. <br /> <br />2. Poor irrigation efficiencies at some sites are due to over <br />irrigation, i.e. fields are irrigated too soon and too long. <br />All of the monitored surface irrigation systems are capable of <br />irrigating at 50% or greater efficiency with proper <br />management. <br /> <br />3. During pre-irrigation of annual crops and first irrigation of <br />perennial crops for stand establishment (e.g. alfalfa), many <br />farmers in the Grand Vall ey app I y a I arge amount of water to <br />"b I ack over" the so i I so that seeds have adequate mo i sture for <br />germination and establ ishment. The el imination of this <br />pract ice wou I d reduce deep perco I at i on substant i a II y (see <br />#5). However, an alternative cultural or management practice <br />wou I d be needed to ensure stand estab Ii shment. <br /> <br />4. Excess pre-irrigation, or the first irrigation, is the <br />biggest contributor to seasonal deep percolation losses. <br />This is directly related to high infiltration rate during <br />these irrigations, which subsequently decreases after the <br />first irrigation. This is supported by the "advance time" <br />data obtained from some of the monitored sites. When <br />infi Itration is high, it takes longer for water to reach <br />the end of the furrow. The "advance time" is less during <br />later i rr i gat ions because of the decrease in i nf i I trat i on rate <br />due to sea ling of the so i I surface. <br /> <br />5. The 1990 data for surface irrigated monitored sites indicate <br />that, on the average, 36% of the seasonal deep percolation <br />losses occurred during the first irrigation event and about <br />48% by the end of second irrigation. For annual crops (beans, <br />small grain and corn), 44% of deep percolation occurred during <br />the first irrigation and about 55% by the completion of the <br />second irrigation. <br /> <br />5 <br />