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<br />000025 <br /> <br />Several hundred soil samples were also taken, at depths up to four feet (Fig. 15), to verifY the results ofthe <br />rapid salinity mapping. The results ofthe soil sample mapping are shown in Table 3 with an average <br />electrical conductivity, ECe, of7.55 dS/m in the top 30 cm of Pivot #7. Readings ranged from a minimum of <br />6.15 to a high of 10.30 dS/m. At the 30-60 cm depth, ECe ranged from 6.74 to 15.63 dS/m with an average <br />of9.67 dS/m. At the 60-90 cm depth, ECe ranged as high as 19.16 with a mean of 10.61 dS/111- <br /> <br />The soil sample readings in Pivot #8 were much less than those in Pivol #7 ranging front a low 00.22 to a <br />high of7.05 and a mean of 4.43 dS/m in the top 30 cm. Maximum ECe reading in Pivot #8 was 14.06 at the <br />60-90 cm depth, Table 8. These readings were mainly responsible for moving the alfalfa production to Pivot <br />#8. <br /> <br />In 1998, readings with an EM-38 by Dr. Tim Gates of the Colorado State University Civil Engineering <br />Department showed salinity readings similar in location to those of Dr. Rhoades but it appears that some <br />of the salts in the middle part of the circle have been leached down on Pivot #7 (Fig. 16). Soil salinity <br />levels, ECe, are below 3.0 dS/m in a large north/south area just east of the center of the circle. Readings <br />up to 10.0 dS/m are still present in the northwest quarter of the circle. Pivot #8 appears to have <br />increased slightly in soil salinity, especially in the northeast quarter of the circle. About 90% of Pivot #8 <br />in 1998 had a salinity level of3.5 dS/m or greater and, at these levels, crop production would be <br />expected to be reduced 10 to 40% when compared to areas of less that 2.0 dS/m (Fig. 17). <br /> <br />Surge lrriltation <br /> <br />Surge irrigation with the use of a computerized, solar powered controller operating aT-type flap valve, s:- [) ) r <br />(Fig. 18), was successfully demonstrated in 1996 but was abandoned in 1997 due to continuing pump, \;'V.-"jJl.; <br />water supply and labor problems. Sorghum-sudangrass iliat was surge irrigated proOUcea equaI'Ytelds of . t-" (\ <br />6 tons per acre but used up to 25% less w~ter as compared to conventional irrigation. The conventional M -r'i ce,Ji, <br />irrigation used a total of20 inches while the surge irrigated area used 15 inches. There was no runoff ~. ~ <br />due to the extreme length of the field which was along the eastern edge of center pivot #4, Figure 1. J'ro ~~l <br /> <br />1999 Colorado Awcultural Outlook Forum and Salinity Workshop ;0?r' " <br /> <br />As part of the grant, Dr. Jim Rhoades and Dr. Gary Banuelos were invited back to Colorado and gave <br />presentations to the 1999 Colorado Agricultural Outlook Forum at the water management session held on <br />February II, 1999 in Denver. Copies oftheir presentations are included, Attachments 7 and 8. <br /> <br />Also as part of the grant, on February 12, 1999, Drs. Rhoades and Banuelos were the main presenters at a <br />Salinity Workshop beld at the Federal Center in Denver. This workshop was attended by more than 50 <br />farmers, technical personnel from various state and federal agencies as well as water district personnel and <br />commercial interest. At the workshop, they were able to expand on the information presented at the Forum. <br /> <br />CWCBPFR9. wpd <br /> <br />28 <br />