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C") co C~ f.:.,) C-.,) ':::) The seasonal and individual application efficiency data shown in Table 2 and individual site summaries is the ratio of water used beneficially to the total irrigation water applied. The calculation is discussed in Appendix C. Table 2 and individual site summary tables show that water budget differed greatly for different sites. All sites applied enough water to meet crop requirements with the exception of site 18, 26 and 51. Most sites over irrigated to cause considerable deep percolation and reduce application efficiency. This is discussed in more detail under irrigation adequacies at sites. Deep Percolation: Most farmers in the Grand Valley tend to over- irrigate no matter what kind of irrigation systems they have. Therefore, deep percolation losses come from on-farm irrigation practices. The seasonal deep percolation losses for the various sites are shown in Table 2 which has been extracted from individual irrigation summaries provided in Appendix D. Also, detailed deep percolation values for each surface irrigated site by irrigation events are provided in Table 3. These are shown in two formats, as acre inches per acre and as a percentage for each individual irrigation event. The average annual deep percolation in the Grand Valley was originally estimated to be 11 acre inches per acre, which results in about four tons of salt pickup per acre foot (see Appendix F) reaching the Colorado River. However, monitoring data for the last seven years indicate the average deep percolation to be slightly over 16 acre inches per acre (Table 4). In 1991, the average deep percolation for all 23 sites was 15.9 inches (Table 2). When only the 20 surface irrigated sites are taken into account, the average deep percolation was 17.3 inches (Table 2). The 20 surface sites consisted of 9 sites with surge system and 11 without surge (conventional irrigation). Deep percolation for the 11 sites was 19.9 inches and 14.0 inches for the 9 surge sites (Table 2). A reduction of six inches in deep percolation was obtained with surge. The average for the three sprinkler and microspray sites is 7.1 inches (Table 2). The deep percolation values shown on Tables 2 and 4 are average values obtained from both surface and sprinkler irrigated sites. In 1991, deep percolation decreased slightly compared to other years. This could be due to one less irrigation overall in 1991 because of cooler weather during the start of the irrigation season. sites 18 and 26/51 had low deep percolation losses because of under-irrigation based on the M&E water budget program. However, actual field moisture determination with hand feel method during the irrigation season showed that there was adequate moisture at 15