Differences in soil water use by annual broomweed and grasses.

Abstract

The use of water in the upper 1 m of the soil profile by 3 common herbaceous species of the southern Great Plains was examined by labeling soil water with 2H2O and H2(18)O. Uptake of labeled water from the 15 cm depth was approximately equal for all species. However, water uptake from the 75 cm depth was significantly greater by annual broomweed [Amphiachyris dracunculoides (DC.) Nutt] than either sideoats grama [Bouteloua curtipendula (Michx.) Torr] or curlymesquite [Hilaria belangeri (Steud.) Nash]. Although both grasses had greater root length density than annual broomweed at the 75 cm depth, annual broomweed's rate of water extraction from the 75 cm depth was nearly twice that of sideoats grama or curlymesquite. Greater access to and more rapid utilization of deeper soil water by annual broomweed relative to the grass species may partially explain annual broomweed's success at invading grasslands and reducing grass production in semi-arid rangelands.