Soil and vegetation of ungrazed crested wheatgrass and native rangelands

Abstract

Seeding of introduced forage grasses, such as crested wheatgrass [Agropyron cristatum (L.) Gaertn. and A. desertorum (Fisch.) Schult.], can lead to the reduction of species diversity and soil quality. This study evaluated the effects of crested wheatgrass on soil and vegetation relative to native rangeland dominated by bluebunch wheatgrass [Pseudoroegneria spicata (Pursh) Scribn. & Smith] under ungrazed conditions. Three sites consisting of adjacent ungrazed stands of crested wheatgrass and native vegetation were sampled in June 1997. Total plant cover was 37% on native and 24% on crested wheatgrass rangeland. Species richness was lower for crested wheatgrass than for native rangeland. Quantities of root biomass and most soil properties were similar for the two rangelands. Native rangeland had a more stable soil structure with 1.7 mm mean weight diameter (MWD) and 38% of soil aggregates in the 2–6 mm size fraction compared to 1.4 mm MWD and 28% of soil aggregate in the 2–6 mm size fraction on crested wheatgrass rangeland. Greater soil penetration resistance was observed at the 6 and 7.5 cm depths for crested wheatgrass rangeland. Crested wheatgrass did not invade adjacent native rangelands and only a slight reduction in soil quality was observed on crested wheatgrass rangelands. Key words: Crested wheatgrass, soil C, soil N, penetration resistance, aggregate stability, species diversity