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<br />The average annual deep perco I at ion in the Grand Va II ey was estimat,ed <br />to be 11 acre inches per acre, '.-Ih i ch resu Its in about four tons of <br />salt pickup per acre foot reaching the Colorado River. However, <br />monitoring data for the last seven years indicate the average deep <br />percolation to be s\ ightly over 16 acre inches per acre (Table 4). <br /> <br />w <br />~. <br />C <br />N <br /> <br />In 1991, the average deep percolation for al I 23 sites was 15.9 inches <br /><Table 2). When only the 20 surface irrigated sites are taken into <br />account, the average deep'percolation is 17.3 inches (Table 2). The' <br />average for the three sprinkler and microspray sites is 7.9 inches <br />(Table 2). The deep percolation values shown on Tables 2 and 4 are <br />average values obtained from both surface and sprinkler irrigated <br />sites. In 1991, deep percolation decreased sl ightly compared to other <br />years. This could be due to one less irrigation overall in 1991 <br />because of cooler weather during start of the irrigation season. <br /> <br />Sites 18 and 26/51 had low deep perco I at i on losses because of 'under- <br />irrigation based on the M&E water budget program, However, actual <br />field moisture determination w,th hand feel method during the <br />irrigation season showed that th.re was adequate moisture at these <br />sites. Producers at sites ,18 and 26 are of the opinion there is high, <br />water table in the fields beIng monitored and that they do not need to <br />irrigate as much. The producer at site 16 is very conscientious of <br />water usage because of limited water for his fields, thus, the site <br />was not ,irrigated as ,muoh. <br /> <br />I <br /> <br />':~.:7~;) <br /> <br />Currently, the monitoring water budget program does not have the <br />capacity to adjust for high water table. Additionally, there is no <br />equipment on hand that could give a quick reliable estimate of soi <br />moisture in the field to make needed adjustments to the computer <br />generated values. <br /> <br />I <br />I <br /> <br />The greatest deep percolation losses occurred at sites 37, 49" ~nd 50 <br />with ove~ 30 inches per acre of deep percolation. In contrast, sites <br />18 and 26/51 had very I ittle deep percolation. These sites were <br />under- i rr i gated as menti oned above. Both of these farmers fo II oW .good <br />irrigation management practices, and try not to over-irrigate. In the <br />past few years they have consistently had no or very I ittle deep <br />percolation. However, sites 32 and 37 with large deep percolation has <br />always had high deep percolation in the last few years. The same <br />producer operate these two fields. <br /> <br />Comparison of sites 31 and 37 show that although they have similar <br />crop, soils and irrigation system the deep percolation losses for site <br />31 was 24.3 i'nches and 36.4 inches for site 37. The difference <br />between the two sites can be attributed to 51 ightly better water <br />management at site 31 compared to site 37. Site 37 had almost 40 <br />inches more water application than site 31, even though site 31 had <br />three more irrigations. <br /> <br />",. <br />.:.-t.: <br /> <br />16 <br />