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Russian wildrye plants were clipped at all possible combinations tion (simulated grazing) on standing crop and vigor of Russian of three clipping dates (April 15, May 15, June 15) at two intensities wildrye. (35 and 65% harvest of current year’s growth). From 19761977 increasing freauencv and httensitv of defoliations increased total Studv Area biomass iemokl oier the I-year-period. There was no trend for ” reduced yield over time with any clipping treatment. However, This study was conducted at the Southeastern Colorado percent plant crown alive (1976-1978) and end-of-season standing Research Center, located 16 km southwest of Springfield in Baca crop (1978) both indicated that increasing frequency and/or intenCounty, Colo. Soils on the study site are Ustollic Haplargids sity of defoliition decreased plant vigor. belonging to the Wiley series. The upper 20 cm are typically silty clay loam in texture, and both wind and water erosion are consiThere are few native grasses capable of providing early spring forage in southeastern Colorado. Of species tested in seeding trials, Russian wildrye (Elymus juncew Fisch.) was found to be the only introduced cool-season grass adapted to the area (Cook et al. 1974). The value of Russian wildrye to ranchers in the South Central Great Plains will depend on itsabilityto withstand defoliation. A dearth of information on grazing adaptability at this latitude exists. Russian wildrye is a long-lived bunchgrass used primarily for range and pasture seedings. This grass is capable of early spring growth (Heinrichs et al. 1976), generally 3-6 weeks earlier than native species. It is very drought tolerant and has an extensive root system, which often reaches 3 m (Rogler and Schaaf 1963). The species is very palatable (Lang et al. 1975) and has a high leaf component (Kilcher 1975). Smoliak and Bezeau (1967) and Heinrichs and Carson (1956) compared important forage species in Canada and found Russian wildrye to have one of the highest crude protein levels throughout all stages of development. Smoliak (1968) noted that 30-year-old stands of Russian wildrye remained productive despite many years of heavy grazing. Frequency, intensity, and season of defoliation are all factors important to the well being of a grass. Generally, grass yields decrease with increasing frequency of defoliation (Buwai and Trlica 1977, Owensby et al. 1974, Everson 1966). However, Cook et al. (1958) found that under favorable conditions crested wheatgrass [Agropyron deserrorum (Fisch.) Schult] yielded more from multiple clippings than from a single autumn clipping. Yields may also decrease as defoliation intensity is increased (Krall et al. 1971, Everson 1966, Neiland and Curtis 1%6, Albertson et al. 1953). However, Frame and Hunt (1971) obtained higher production from perennial ryegrass (Loliumperenne L.) swards as intensity of clipping was increased. Cook et al. (1958) reported that spring harvested crested wheatgrass plants produced a lower 5-year total yield than plants clipped in early summer, but were producing more at the end of the experiment. Similarly, Drawe et al. (1975) found that of various clipping treatments, Russian wildrye plants clipped early produced the least forage, but maintained the highest vigor. The objective of this study was to evaluate the effect of defoliaAuthors were research assistant and associate professor, respectively, De.partment of Range Science, Colorado State University, Fort Collins, 80523. Svejcar’s present address is Rangeland Resources Program, Oregon State University, Corvallis, Oregon 91331. This study was supported by the Colorado State Univ. Exp. Sta. and published as Scientific Series 2595. Manuscript received October 2, 1980. dered problems on this soil (Woodyard et al. 1975). The climate and vegetation are typical of the South Central Great Plains. The shortgrasses, blue grama [Boutelouo gracilis (H.B.K.) Lag.] and buffalograss [Buchloe ductyloides (Nutt.) Engelm.] dominate the native vegetation. Average annual precipiation between 1957 and 1978 was 38.8 cm. Annual precipitation was 25.7,39.1,40.8,56.6, and 33.9 cm for 1974 through 1978, respectively. Average pan evaporation and wind speed during the study were 187.5 cm and 6.2 km per hour, respectively. The study site was used for sorghum [Sorghum bicolor (L.) Moench] research prior to the first Russian wildrye planting in 1968. Russian wildrye was seeded into sorghum stubble in early spring each year from 1968 through 1971; however, unfavorable climatic conditions caused the 1970 planting to be unsuccessful. Materials and Methods Clipping treatments imposed on Russian wildrye from 1974 through 1977 involved three clipping dates (4-15, 5-15, 6-15) and two intensities (35 and 65% harvest of current year’s growth). Plants were clipped at the seven possible combinations of the three clipping dates within each intensity (Table 1). Thus, plants were clipped either once, twice, or three times during the season (frequency 1,2, and 3, respectively), or in the case of controls were left unclipped. These dates correspond to the potential defoliation periods of various grazing regimes. Plants were clipped at 35 or 65% of current year’s growth at the time of clipping (light and moderate clipping, respectively). Clippings of individual plants were oven dried at 65’C for 24 hours, and weighed. Measurements considered indicative of plant vigor were taken during the third week in August of 1976, 1977, and 1978. The measurements consisted of two perpendicular diameters of each plant and a rating of degree of plant crown alive. The rating was on a scale from zero to four, where 0 = O%, I = 25%, 2 = 50%, 3 = 75%, and 4 = 100% live plant crown. During 1978 all plants were allowed to grow unhindered until the end of August, when they were clipped to ground level to determine total standing crop as affected by previous year of treatment. Russian wildrye stands planted in 1968, 1969, and 1971 were used as replications. Each planting consisted of five drill rows, with row spacings of 35 cm. Transects were taken across the drill rows, and the plant in each drill row closest to the transect was assigned to an experimental unit. Thus, there were 5 plants per experimental unit. There were two complete sets of treatments within each replication. Treatments were randomly assigned within replica594 JOURNAL OF RANGE MANAGEMENT 35(5), September 1982 Table 1. Clipping treatments imposed on Russian wiidrye during 1974 through 1977. Dashes indicate plants were clipped on that date. Treatment number’ April I5 May I5 June 15

Standing Crop and Vigor of Defoliated Russian Wildrye in Southeastern Colorado