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<br />(\~J <br /> <br />Reduction in infi Itrated depth and deep percolation helped increase <br />app I i cat i on eff i c i ency at surge sites by an average of 4.7Y. in 1991 <br />and about l2Y. iri 1990. The difference in application efficiency <br />between surge and conventional sites varied from a low of -0.6Y. to a <br />high of9.5Y. for the season <Table 5). <br /> <br />w <br />~' - <br />@ <br />~, <br /> <br />The difference in deep percolation reduction with use of, surge <br />i~rigation system varied from 0.5 acre inches to 9.9 acre inches per <br />acre. The site (50) with the least deep percolation savings also did <br />not have the first irrigation monitored in the fall of the prior year. <br />Had fall irrigation been monitored, the savings could have been <br />substantially more since almost 50Y. of fall grain deep percolation <br />occur by the end of the first irrigation. The comparison shows that <br />deep percolation could be reduced by about 4.3 acre inches per acre <br />with the use of surge systems, a savings of 21Y. for the season (Table <br />5) . <br /> <br />e. Trends <br /> <br />Irrigation Trends: A comparison of seven years of irrigation data <br />(Tab I e 4) shows that in 1990 deep perco I at ion i'ncreased 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 />'-';0, <br />':i::,/ 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, sti I I have the same crop as 1985. In the <br />Grand Valley, fields that are in annual crops or alfalfa'go through a <br />crop rotation. This makes it impossible to compare all individual <br />monitored sites for different years, Comparison of seven year of <br />ir~igatidn monitoring data by crops (Table 6) show no trend towards <br />decrease in water u'se or' -deep per-co I at i on. Severa I years of data .are <br />needed before any trend can be determined. Unti I good irrigation <br />water management practice is applied in the field, and signifi,cant <br />amount of reduction in water use and deep pel"'"colation and increase in <br />irrigation efficiency ooours, a trend wi I I not be seen. <br /> <br />Salinity Trends: During the fal I, for the past eight years (1984- <br />1991), quantitative salt determinations have been made at depths of 6, <br />18, and 30 inches for eaoh monitoring site. Soi I samples were <br />co II ected each year from approx i mate I y the same area. Each mon i tori ng <br />site was sampled in two locations, the top and the bottom of the <br />monitoring fields. <br /> <br />At most sites, salinity levels are relatively low (refer to Appendix E <br />for sal inity data). Fifty to seventy years of irrigating these soi Is <br />have reduced sal inity levels to very low values. However, sal inity <br />levels measured during <br /> <br />21 <br />