Growth, Water‐Use Efficiency, and Digestibility of Crested, Intermediate, and Western Wheatgrass

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AbstractRelationships between dry matter distribution among plant components, growth rates, in vitro digestible organic matter (IVDOM), and water‐use efficiency (WUE) have not been defined for cool‐season wheatgrass species grown on the Northern Great Plains. Three cultivars each of crested wheatgrass [Agropyron desertorum (Fisch. ex Link) Schult.], intermediate wheatgrass [Elyfrigia intermedia (Host) Nevsk: Syn: A. infermedium (Host) Beauv.], and western wheatgrass (Pascopyrum smithii (Rhdb.) Love Syn: A. smithii Rydb.] were field grown and sampled over a 3‐yr period to define these relationships. The soil was a Parshall fine sandy loam (coarse‐loamy, mixed Pachic Haploboroll). Forage was harvested at three dates to measure IVDOM, WUE, forage yield, leaf area index (LAI), and leaf and stem dry matter. Significant differences were mainly present among cultivars of western wheatgrass compared to those of crested and intermediate wheatgrass. ‘Rodan’ western wheatgrass partitioned more dry matter into stems than leaves, which resulted in lower LAI, leaf/stem ratio (LSR), and IVDOM. However, Rodan had higher WUE and forage yield than did ‘Flintlock’ and ‘Rosana’ western wheatgrass. Although forage yield and IVDOM differed among western wheatgrass cultivars, there were no differences in total digestible organic matter. Growth analysis showed Rodan western wheatgrass to be more efficient than Flintlock and Rosana in accumulation of dry matter per unit of photosynthesizing leaf surface. These results suggest that partitioning of dry matter into leaves and stems is a primary factor in determining WUE and digestibility, especially for western wheatgrass.