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Description:
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Studies of soil water use by forage and competitive deep -rooted brush species are needed to make brush management decisions in the seiaiarid southwestern United States . A study was conducted on a sandy soil in west Texas supporting a dense stand of sand shin oak (Quercus havardii ) and an adjacent area treated with tebuthiuron in 1978 to control the shin oak . Root and rhizome distributions were estimated by auger extraction and washing , and forage yield was estimated by clipping . Both total and available soil water , water use , and water use efficiency were estimated by neutron scattering in 1981 and 1982 . Measurable soil water savings began at the first herbicide -induced resprouting cycle of shin oak . Available water tended to be higher in the grass -forb community which remained after herbicide removal of the shin oak than in the shin oak -grass community . Water use efficiency was higher in shin oak -grass vegetation than in the grass -forb vegetation . Clipping , or simulated grazing , had minimal effect on water use efficiency of vegetation in the grass -forb community . Although sand shin oak efficiently uses water , the water used could be used by more desirable vegetation . Shin oak has a deeper effective rooting depth than most associated herbaceous plants . The grasses and forbs remaining after shin oak control extended their effective rooting depths to take advantage of additional available water . Soil water potentials were higher below 137 cm (effective rooting depth of herbaceous plants ) in the herbicide - treated area than in the untreated area . Shin oak developed and maintained more negative midday leaf water potentials than associated plants ( -25 to -30 bars ) . Most plants had more negative midday leaf water potentials in shin oak areas than in herbicidetreated areas because less soil water was available to them . Shin oak is the dominant plant on sandy soils within its range because of its morphological and physiological adaptations . To simulate short -duration grazing , or when the oak -grass vegetation was compared to shin oak alone after all understory species had been removed by hand . Therefore , sand shin oak can be considered an efficient user of rainfall for aboveground biomass production in its native environment in west Texas . |