Control of the soil water balance by sagebrush and three perennial grasses in a cold‐desert environment

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Abstract
This study compared the capacity of monocultural stands of crested wheatgrass, giant wildrye, streambank wheatgrass, and Wyoming big sagebrush to deplete water from a clay‐loam soil. Soil water balance of a natural sagebrush steppe was used as a reference point. Transplanted crested wheatgrass plants extracted 243 mm of water from the soil during the first growing season, using most of the plant‐available water. The other species extracted less water, but evapotranspiration from all stands was well over the average annual precipitation for the study area (224 mm). In the second year, all four species extracted water from the entire 2.2‐m profile and used most of the available water. The native community removed essentially all of the available soil moisture in each of the three years. Despite phenological and morphological differences among species, patterns of water depletion were generally similar. Seasonal evapotranspiration varied little among species but was correlated with the soil water available at the beginning of the growing season. Early in the season, the grasses extracted water more rapidly than did sagebrush or a natural sagebrush steppe, but during the period of most rapid water depletion, relative rates of extraction varied little. All four species depleted volumetric soil water content to a lower limit of 11–12%. The effective water storage capacity of the soil was 20% by volume. The results indicate that 1.4 m of soil would be adequate to store the maximum precipitation that might be received outside the growing season and thereby preclude drainage into interred wastes.