Plant and soil water relationships following sand shin oak control



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Texas Tech University


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.



Oak -- Control, Soil moisture, Plant-water relationships