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non-irrigated control received no supplemental water. Since there was little or no <br />treatment difference due to irrigation level during 2005, perhaps due to the high levels of <br />rainfall throughout that growing season, treatment levels during 2006 were reduced in <br />half to 0.65, 0.3, and 0.15 gal/day/tree for the high, medium, and low irrigation levels, <br />equivalent to 7.2, 3.6, and 1.8 inches of precipitation per month. Irrigation treatments <br />were applied daily during the early morning, from June 9, 2006 to October 4, 2006. <br />Drippers required 4 Ibs pressure for activation. The valve box and distribution lines were <br />configured so that head pressure down stream of the valves did not exceed this value to <br />avoid leakage between irrigation treatments, Soil moisture and temperature sensors <br />were located in each plot and data were recorded hourly. Because of the unreliability of <br />the soil moisture sensors during 2005, gravimetric soil samples were collected <br />periodically throughout the 2006 season from each irrigation treatment. Samples were <br />sealed and transported to the lab where they were weighed, then dried and re-weighed <br />for moisture content. Additional samples were collected from each irrigation treatment <br />for chemical analysis. Soil chemical analysis and soil moisture were also conducted on <br />soil samples collected from an undisturbed aspen stand about'/ km south of the <br />experimental plot. <br />Standard meteorological conditions were monitored at an automated weather <br />station located at the center of the plot, and data recorded hourly included wind speed, <br />wind direction, air temperature, relative humidity, and precipitation. Hourly soil <br />temperature, moisture content, and matrix potential were also monitored at one tree in <br />each watering treatment. All data were recorded on a Campbell 23x data logger, which <br />was also programmed to activate the irrigation solenoids. Power was supplied by 12 V <br />batteries charged by a solar panel. <br />In addition to the transplanted aspen in the irrigation study, we also obtained <br />growth and survival data from two other types of young aspen trees: 1) Natural sprouts <br />that had grown from roots buried in un-irrigated areas of the roto-cleared and dozer- <br />cleared soil adjacent to the irrigated blocks; and 2) commercially-grown potted aspen <br />seedlings that were planted in an non-irrigated fenced area approx 1 km from the <br />irrigation study site. It was not determined if the roots grew out of the potting mix into the <br />surrounding soil during the first or second year of study. Lateral distribution of rooting <br />8 <br />