A comparative index to digestible nutrients was established for Russian wildrye, crested wheatgrass, and intermediate wheatgrass seeded on foothill areas of Utah. The nutritive values of these grasses were compared by the lignin ratio method, the chlorophyllan ratio method, and the in vivo rumen bag process. Average digestion coefficients computed by the lignin ratio method for dry matter, ether extract, cellulose, and gross energy were highest for intermediate wheatgrass. Protein was more digestible for Russian wildrye. Digestible energy was adequate in all species to meet requirements for late lactation. Results from the chlorophyllan ratio method were excessively high and were not considered valid. Dry matter loss of Russian Wildrye was greater than losses from either of the wheatgrasses. Losses of dry matter due to 24-hour in vivo rumen fermentation and rinsing only of nylon bags were closely correlated.

The effects of grazing and moisture availability on the competitive interactions of intermediate wheatgrass (Thinopyrum intermedium (Host) Barkw. & D.R. Dewey) and western wheatgrass (Pascopyrum smithii (Rhydb.) A. Love) were examined under a short-duration grazing system in central Utah. The fate of tiller cohorts was observed at approximately monthly intervals at the interface between patches of these two rhizomatous grasses and in monospecific stands. The effects of short-duration grazing, clipping of western wheatgrass following grazing to achieve levels of utilization equivalent to that of intermediate wheatgrass, irrigation, and removal of the competitor were assessed in terms of the recruitment, longevity, and mortality of ramets of both species. The effects of severance of clonal connections and defoliation on the performance of young shoots of both species were also studied. The tiller dynamics of the two species differed greatly. Maximum life span of intermediate wheatgrass tillers was approximately 18 months, while that of western wheatgrass tillers exceeded the 3.5-year observation period. Tiller turnover was higher in intermediate wheatgrass than in western wheatgrass. Defoliation tended to increase the mortality risk of intermediate wheatgrass ramets but not that of western wheatgrass ramets. Supplemental water had the opposite effect. Irrigation increased the probability of ramet survival for intermediate wheatgrass during the growing season but led to higher winter mortality for western wheatgrass ramets. During the four years of this study (1987-1990), western wheatgrass was the competitive dominant species. Recruitment of intermediate wheatgrass ramets at the interface was reduced compared to monospecific stands while that of western wheatgrass was enhanced. The mortality of intermediate wheatgrass tillers increased as a result of competition with western wheatgrass but only when plants were grazed. Competition had little effect on the mortality of western wheatgrass ramets. The competitive ability of intermediate wheatgrass versus western wheatgrass improved when both species were grazed heavily and when plants were irrigated.

Due to increased environmental stewardship and fertilizer prices, there is increased interest in using legume mixes in perennial croplands. The objective of this study was to compare quantitative genetic parameters and quantitative trait loci (QTLs) associated with intermediate wheatgrass (Thinopyrum intermedium) when grown in 1) a non-competitive spaced environment, 2) a polyculture with alfalfa (Medicago sativa), and 3) a monoculture with crested wheatgrass (Agropyron desertorum). Traits evaluated include plant growth characteristics (Zadok’s maturity, height, and tiller count), biomass, and forage nutritive value (CP, NDF, ADF, ADL, IVTD, NDFD, NFC, ME, RFQ). A linkage map comprised of 3568 single nucleotide polymorphisms in 21 linkage groups corresponding to 21 homologous chromosome pairs of both parents was used to identify QTLs and QTL x environment interactions (QxE) based on trait averages for each genotype in each environment. Significant genotype x environment interactions were detected for biomass, NDF etc. A total of 26 QTLs were identified, including 6 MASS, 2 TILE, 2 TICR, 1 ZAMA, 1 CP, 3 NDF, 2 ADF, 3 IVTD, and 5 NDFD. A subset of 7 QTLs showed significant QxE interaction. These results indicate that breeders need to evaluate plants in polyculture or swards if these are the intended crop management systems.

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