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<br />alternative cultural or management practices that are economically <br />benefical would be needed to ensure stand establishment. <br /> <br />l\:) <br />r'~) <br />C'O <br />::Jl <br /> <br />Excess pre-irrigation or the first irrigation, is the biggest <br />contributor to seasonal deep percolation. This is directly related <br />to high infiltration rates during these irrigations, which <br />subsequently decrease after the first irrigation. This is <br />supported by the "advance time" data obtained from some of the <br />monitored sites. When infiltration is high, it takes longer for <br />water to reach the end of the furrow. The "advance time" is less <br />during later irrigations because infiltration rate decreases due to <br />sealing of the soil surface. <br /> <br />The 1995 data for surface irrigated monitored sites indicate that, <br />on the average, about 23% of the seasonal deep percolation losses <br />occurred during the first irrigation event and about 33% by the end <br />of second irrigation. <br /> <br />Several years of monitoring data from improved surface and <br />sprinkler irrigated sites indicate that the overall average deep <br />percolation for the Grand Valley is 15.8 acre inches per acre. In <br />1995 deep percolation from surface irrigation alone was 11.9 acre <br />inches per year. <br /> <br />Deep percolation from surface sites could be reduced by as much as <br />20 to 30% with ,use of surge irrigation techniques (Table 2). Surge <br />irrigation reduced deep percolation by 10.5 inches in 1992 and, six <br />inches in 1991. A reduction of 50 to 80% could be realized by <br />converting to sprinklers. The use of sideroll sprinklers is <br />limited by the cost of pressurizing the system and the elimination <br />of corn as a crop alternative. <br /> <br />side-by-side comparison of surge sites with conventional sites <br />during 1991, 1992 and 1993 showed that surge could reduce total <br />water application, tailwater runoff and deep percolation by as much <br />as 20 to 30%. ' <br /> <br />Where improved irrigation systems have been installed, the deep <br />percolation losses can be reduced substantially by proper <br />management of individual irrigation events. Reducing set time <br />(number of hours per set) and waiting longer between irrigations <br />(irrigation scheduling) would reduce deep percolation <br />significantly, and also increase irrigation efficiency. <br /> <br />summary Of Water Budget, Deep percolation And Application Efficiency <br /> <br />Water Budget: The results of the 1995 irrigation monitoring evaluations <br />from the eight sites are presented in Table 2. All irrigation events, <br />including pre-irrigation events, were monitored for all sites. Table 2 <br />summarizes the seasonal data obtained from the eight irrigation <br />monitoring sites and also shows data by crops and irrigation systems. <br />The data in Table 2 represents the total inflows and outflows for each <br />field, total deep percolation and ET for all irrigations during the 1995 <br />irrigation season. The information on Table 2 has been extracted from <br />individual irrigation summaries which will be provided upon request from <br />the NRCS. <br /> <br />8 <br />