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<br />"J <br />,'- <br />c,..) <br />....... <br /> <br />.::1 <br /> <br />.:.:' <br /> <br />1990 could be attributed to over irrigation during the early part of <br />the irrigation season because of anticipated water shortage in the <br />summer. <br /> <br />In 1990, using 16.1 acre inches per acre of deep percolation as a <br />standard for the Grand Va I ley (obta i ned from six years of data), 14 <br />sites demonstrated practices which kept deep percolation losses below <br />16.1 inches <Table 5). Eleven sites (mostly annuals) had considerably <br />higher deep percolation than the six year average. This offset the <br />benefits derived from lower deep percolation from the 14 sites. As a <br />result the average deep percolation and salt load reduction came o~t <br />to be -0.86 acre inches and -0.26 tons per acre (Table 5 - negative <br />values represent salt loading greater than average) respectively. <br /> <br />Some of the sites had low deep percolation losses because of under- <br />irrigation based on the M&E water budget program. However, actual <br />field moisture determination with hand feel method during the <br />irrigation season showed that there was adequate moisture at sites <br />18, 26, and 29 compared to what the M&E data showed. Producers at <br />sites 18 and 26 are of the opinion there is high water table in the <br />fields being monitored and that they do not need to irrigate as much. <br />Site 29 seems to have a high water table also. At this site, normal <br />irrigation schedul ing was followed. There was excess deep percolation <br />during the first fall and spring irrigation (Refer to Appendix B) but <br />not as excessive compared to other sites. The producer at site 16 is <br />very conscientious of water usage because of I imited water for his <br />fields, thus, the site was not irrigated as much. <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 rei iable estimate of soi I <br />moisture in the field to make needed adjustments to the computer <br />generated values. <br /> <br />The greatest deep percolation losses occurred at sites 27 and 32 with <br />about 42 acre inches per acre. In contrast, sites 16 and 26 had no <br />deep percolation. These sites were under-irrigated as mentioned <br />above. Although site 18 has high water table, site 16 does not. Both <br />of these farmers follow good irrigation management practices, and try <br />not to over-irrigate. In the past few years they have consistently <br />had no or very I ittle deep percolation. However, sites 27 and 32 with <br />large deep percolation has always had high deep percolation in the <br />last few years. <br /> <br />Comparison of sites 31 and 37 show that although they have simi lar <br />crop, soils and irrigation system the deep percolation losses for site <br />31 was 16.4 inches and 39.2 inches for site 37. The difference <br />between the two sites can be attributed to better water management at <br />site 31 compared to site 37. Site 37 had more than 20 inches more <br />water appl ication than site 37, even though site 31 had two more <br />irrigations. <br /> <br />18 <br />