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<br />, (D <br />C) <br />C'? <br />o <br />,:-) <br /> <br />.'- <br />-' <br /> <br />The difference in deep percolation reduction with use of surge <br />irrigation system varied from 0.5 acre inches to 9.9 acre inches <br />per acre. site 50 with the least deep percolation savings also did <br />not have the first irrigation monitored in the fall of the prior <br />year. Had fall irrigation been monitored, the savings could have <br />been substantially more since almost 50% of fall grain deep <br />percolation occurs by the end of the first irrigation. The <br />comparison shows that deep percolation could be reduced by about <br />4.3 acre inches per acre with the use of surge systems, a savings <br />of 21% for the season (Table 5). <br /> <br />e. Trends <br /> <br />Irrigation Trends: A comparison of seven years of irrigation data <br />(Table 4) shows that in 1990 deep percolation increased compared to <br />1986 through 1989, but is less than 1985. In 1991, both deep <br />percolation and water use decreased slightly compared to 1990. <br /> <br />Of the 16 original sites started in 1985, only six of them were <br />monitored through 1991: sites 11, 15-18, and 21. Of the six sites, <br />only two sites, 11 and 17, still have the same crop as 1985. In <br />the Grand Valley, fields that are in annual crops or alfalfa go <br />through a crop rotation. This makes it impossible to compare <br />individual monitored sites for different years. Comparison of <br />seven years of irrigation monitoring data by crops (Table 6) show <br />no trend toward decrease in water use or deep percolation. until <br />good irrigation water management is applied in the field to <br />significantly reduce the amount of water use and deep percolation, <br />a change will not be seen. <br /> <br />Salinity Trends: During the fall, for the past eight years (1984- <br />1991), quantitative salt determinations have been made at depths of <br />6, 18, and 30 inches for each monitoring site. Soil samples were <br />collected each year from approximately the same area. Each <br />monitoring site was sampled in two locations, the top and the <br />bottom of the monitoring fields. <br /> <br />At most sites, salinity levels are relatively low (refer to <br />Appendix E for salinity data). Fifty to seventy years of <br />irrigating these soils have reduced salinity levels to very low <br />values. <br /> <br />However, salinity levels measured during the sampling in the fall <br />of 1991 gave a confusing picture. sites 11, 13, 15, 16, 21, 32, <br />43, and 45 had significantly higher salinity than measured in the <br />past. <br /> <br />Salinity levels measured were about the same as levels measured in <br />previous years at one point in a field while the second point had <br /> <br />22 <br />