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20 November 2020 Suppression of Cheatgrass by Perennial Bunchgrasses
Robert R. Blank, Charlie Clements, Tye Morgan, Dan Harmon, Fay Allen
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Long-term control of the invasive annual grass cheatgrass is predicated on its biological suppression. Perennial grasses vary in their suppressive ability. We compared the ability of a non-native grass (“Hycrest” crested wheatgrass) and two native grasses (Snake River wheatgrass and bluebunch wheatgrass) to suppress cheatgrass. In a greenhouse in separate tubs, 5 replicates of each perennial grass were established for 96 d, on which two seeds of cheatgrass, 15 cm apart, were then sown in a semicircular pattern at distances of 10 cm, 30 cm, and 80 cm from the established perennial bunchgrasses. Water was not limiting. After 60 d growth, cheatgrass plants were harvested, dried, weight recorded, and tissue C and N quantified. Soil N availability was quantified at each location where cheatgrass was sown, both before sowing and after harvest. Relative to cheatgrass grown at 80 cm, all perennial grasses significantly reduced aboveground biomass at 30 cm (68% average reduction) and at 10 cm (98% average reduction). Sown at 10 cm from established perennial grasses, cheatgrass aboveground biomass was inversely related with perennial grass root mass per unit volume of soil. All cheatgrass sown at 10 cm from “Hycrest” crested wheatgrass died within 38 d. Before sowing of cheatgrass, soil 10 cm from established perennial grasses had significantly less mineral N than soil taken at 30 cm and 80 cm. Relative to cheatgrass tissue N for plants grown at 80 cm, cheatgrass nearest to the established perennial grasses contained significantly less tissue N. All perennial grasses inhibited the NO2 to NO3 nitrification step; for “Hycrest” crested wheatgrass, soil taken at 10 cm from the plant had a molar proportion of NO2 in the NO2 + NO3 pool of > 90%. In summary, a combination of reduced nitrogen availability, occupation of soil space by perennial roots, and attenuation of the nitrogen cycle all contributed to suppression of cheatgrass.

Published by Elsevier Inc. on behalf of The Society for Range Management.
Robert R. Blank, Charlie Clements, Tye Morgan, Dan Harmon, and Fay Allen "Suppression of Cheatgrass by Perennial Bunchgrasses," Rangeland Ecology and Management 73(6), 766-771, (20 November 2020).
Received: 23 October 2019; Accepted: 18 April 2020; Published: 20 November 2020

Agropyron cristatum
Bromus tectorum
Elymus wawawaiensis
plant suppression
Pseudoroegneria spicata
soil nitrogen availability
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