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Tests done by Dr. Jim Rhoades, Director of the US Salinity Lab and his field team in April, 1996 confinned the high salt levels, however, these high salt levels were point located using readings from an EM-38, a sensor which produces an electromagnetic field that penetrates the soil causing an electrical current flow within the soil profile. These readings indicated that the most saline part of the field was located in the northwest quarter of Pivot #7. The average was 7.6 dS/m with readings up to 10.3 dS/m or mmhos/cm in the surface foot. These readings were supported by ground site soil samples. Readings, ~ "L 1 . . in Pivot #8 averaged 4.4 dS/m ranging up to 7.1 dS/m in the surface foot. -w~'nW' 17\<Q'tO \J vv,J Again in 1998, readings with an EM-38 by Dr. Tim Gates of the Colorado State University I~; ~ Civil Engineering Department showed salinity readings similar in location to those of Dr. Rhoades but it :J ~ appears that some of the salts in the middle part of the circle have been leached down on Pivot #7. Soil . ~ : salinity levels, ECe, are below 3.0 dS/m in a large north/south area just east of the center of the circle. ~>I1f: Readings up to 10.0 dS/m are stilI present in the northwest quarter of the circle. Pivot #8 appears to have . . increased slightly in soil salinity, especially in the northeast quarter of the circle. About 90% of Pivot #8 in 1998 had a salinity level of3.5 dS/m or l(reater and, at these levels. cron production 'Yould ~e expected to be reduced 10 to 40%J:Yhen crmpar"el to ar"3~ !RIess that 2.0 d~/m. ~ ~h;{--.~ I" d- "'~ G Salinity was also high in the water from wells being used to irrigate the two center pivots. Water in pump #14 which supplied Pivot #7 was tested in December, 1994 at 4.6 dS/m and 4.2 dS/m when tested in July of 1995 and up.!Q2.2 dS/m in August 1995. O~r wells, used on Pivot #8, test~ in tI:!~J& dS/m range. Salinity levels continued in this range durmg the demonstration period. Nitrate-nitrogen was average on both fields except in the Bloom silt loam on Pivot #8 where it ranged up to 164 ppm. Small grains and forage crops had been grown in each of the fields so amounts of nitrogen applied were lower than would have been applied to corn or other high nitrogen use crops. Alfalfa and other legumes and grasses and/or grass-legume mixtures were used in the demonstration as they are more salt tolerant than some other crops and normally have lower water and/or nitrate use which should reduce salt and nitrate loading. ~ was planted on Pivot #7 in the late summer of 1995 but excessive rains in August and the high salt content of the soil and irrigation water caused a tptal crop failure. Looking for forage crops with more salt tolerance, grasses ~d sorghum-su~ass were J:llanted in 1996, again resulting in a crop M~ ~ as adequate stands were not achieved. In 1997, the area was again planted to sorghum- sudangrass. The crop came up to a excellent stand but, once the roots reache3 the second foot, the plants became stunted and the crop was overtaken by weeds The high salts in the water and in the lower root zone was considered to be the reason for the continuing crop failure. ----:..-- This was confinned by a greenhouse study conducted in cooperation with Dr. Gary Banuelos of the USDA-ARS Water Management Research Laboratory in Fresno, CA. Soils from Pivot #7 were sent to the laboratory, potted and irrigated with water synthetically constructed based on analysis from samples of river and well water. Tall fescue and Birdsfoot trefoil, both broad leaf and narrow leaf; were tested. "Salt toxicity as burning of the leaf margins and stunting of growth began 10 appear in all three species shortly after applying the poor IT quality water" (Ref. #1) from the well. However, tge.taIl fesc!,e ptoduced acceptable amounts of el1:Y matter, nearly twice the dry matter produced by the Birdsfoot trefoil. 2