Herbicide Treatment Effects on Properties of Mountain Big Sagebrush Soils after Fourteen Years

Soil properties under stands of vegetation dominated by mountain big sagebrush ( Artemisia tridentata ssp. vaseyana ) and grass were examined 14 yr after spraying with 2,4‐dichlorophenoxy acetic acid (2,4‐D) to control sagebrush. Changes in only a few soil chemical properties were found after conversion to grassland. Phosphorus and K were apparently redistributed from depth to the surface 5 cm of soil by grass‐dominated vegetation. Conversely, surface concentrations of N were lower under grass vegetation than under undisturbed vegetation. No changes attributable to vegetation conversion were found for total C, Na, Mg, cation exchange capacity, base saturation, pH, bulk density, or potential net N mineralization rates at any depth. In situ net N mineralization rates at a 5‐ to 15‐cm depth were measured under and between shrubs for both vegetation conditions 15 yr after spraying. Nitrogen mineralization was similar from positions between and under former shrubs in converted (grass) vegetation, whereas in the sagebrush vegetation, mineralization rates were higher under live sagebrush plants than in interspaces between plants. Undershrub net N mineralization rates were higher under shrubs in the sagebrush vegetation than under former shrubs in the grass vegetation. Essentially, control of big sagebrush, in the absence of grazing, had no effect on site fertility. The spatial distributions of the elements and of their cycling, however, have been altered.