Published in Crop Sci. 44:1385-1390 (2004).
© 2004 Crop Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
FORAGE & GRAZING LANDS
Nutritive Value of Virginia Wildrye, a Cool-Season Grass Native to the Northeast USA
Matt A. Sandersona,*,
R. Howard Skinnera,
Martin van der Grintenc and
Jennifer Kujawskib
a USDA-ARS Pasture Systems and Watershed Management Research Unit, Bldg 3702, Curtin Road, University Park, PA 16802-3702
b USDA-NRCS National Plant Materials Center, Beltsville, MD 20705
c USDA-NRCS Plant Materials Center, Big Flats, NY 14830
* Corresponding author (mas44{at}psu.edu).
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ABSTRACT
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Interest in native plant species for conservation and production has increased because of new federal policies. We evaluated accessions of the native cool-season grass Virginia wildrye (Elymus virginicus L.) from the northeastern USA for nutritive value and its association with plant morphological traits. Thirteen accessions, one cultivar (Omaha), and one commercial ecotype of Elymus were transplanted into single-row field plots in late summer of 2000 at Beltsville, MD, Rock Springs, PA, and Big Flats, NY. Two orchardgrass (Dactylis glomerata L.) cultivars were included. Primary growth was harvested in April (Beltsville) or May (Rock Springs and Big Flats) of 2001 and 2002 and analyzed for neutral detergent fiber (NDF), crude protein (CP), and digestible NDF (dNDF). Nutritive value measures were related to plant morphological attributes [leaf width, length, area, and leaf-to-stem mass ratio (LSR)]. Virginia wildrye accessions differed (P < 0.01) in nutritive value and often had lower NDF and higher CP and dNDF than the commercial ecotype, Omaha cultivar, and orchardgrass. The LSR accounted for most of the variation in nutritive value. Orchardgrass was more mature at harvest than Elymus entries and thus lower in nutritive value. Neutral detergent fiber was negatively correlated with LSR (r = –0.26 to –0.74, P < 0.05), whereas CP and dNDF were positively correlated (r = 0.36 to 0.80 for CP and 0.44 to 0.74 for dNDF, P < 0.05). Neutral detergent fiber was also positively correlated (r = 0.27 to 0.86, P < 0.05) with leaf length. Virginia wildrye is comparable to other cool-season grasses in nutritive value.
Abbreviations: ADF, acid detergent fiber • CP, crude protein • dNDF, digestible neutral detergent fiber • IVTD, in vitro true digestibility • LSR, leaf-to-stem mass ratio • NDF, neutral detergent fiber • SLA, specific leaf area
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INTRODUCTION
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MOST FORAGE GRASSES grown in the northeastern USA are introduced species such as orchardgrass, bluegrass (Poa spp.), or tall fescue (Festuca arundinacea Schreb.). Native warm-season perennials, such as switchgrass (Panicum virgatum L.) and big bluestem (Andropogon gerardii Vitman), account for most of the native grasses used in forage systems. Few, if any, native cool-season grasses have been evaluated as potential forage species in the northeastern USA. New federal policies related to invasive species, conservation plantings, and farm programs have created greater interest in native plants for conservation and production during recent years (Richards et al., 1998; Federal Register, 1999).
Virginia wildrye, a perennial cool-season grass native to the northeastern USA, grows along streams, forest margins, and in other moist areas (Pohl, 1947; Hitchcock, 1971). It is recommended as a component in some conservation plantings for revegetation. Asay and Jensen (1996) considered Canada wildrye (E. canadensis L.), blue wildrye (E. glaucus Buckley), and Dahurian wildrye (E. dahuricus Turcz ex Greiseb) the most noteworthy of the Elymus wildryes as forages and briefly mentioned Virginia wildrye for revegetating prairie (Asay and Jensen, 1996). Closely related, both Virginia wildrye and Canada wildrye are highly self-fertile allotetraploids (2n = 28) with the SSHH genome constitution (Asay and Jensen, 1996). Very little breeding has been done in either species. In an evaluation of 30 grass species in Saskatchewan, Canada, Virginia wildrye was considered a promising forage grass, but lack of winter hardiness limited its persistence (Lawrence, 1978). Hereafter in this paper, the terms "Elymus" and "wildrye" will refer to E. virginicus.
Genetic variation for nutritive value occurs within many species of cool-season introduced grasses (Casler et al., 1996). Sometimes the variation in nutritive value results simply from differences in maturity or plant morphology. For example, the LSR of grasses typically declines with maturity and is accompanied by a decrease in nutritive value (Nelson and Moser, 1994). Nutritive value of grasses, however, can be improved by changing the cell wall composition without affecting plant maturity or gross morphology [e.g., in smooth bromegrass (Bromus inermis Leyss); Casler and Carpenter, 1989]. Plant morphology can influence other traits related to livestock performance. For example, leaf width in tall fescue was negatively related to leaf tensile strength and, hence, positively related to preference by grazing cattle (MacAdam and Mayland, 2003).
Greater interest in the use of native grass species in conservation and other plantings has created a need for more information on the suitability of locally adapted native species for the northeastern USA. We could not find any information on the nutritive value of Elymus as a forage grass in the northeastern USA. Previously, we reported on the productivity, morphology, and persistence of several Elymus accessions at three locations in the northeastern USA (Sanderson et al., 2004). Our objective in this study was to evaluate the same northeastern accessions of Virginia wildrye for nutritive value.
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MATERIALS AND METHODS
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The experiment was conducted at the USDA-NRCS Plant Materials Center in Big Flats, NY (42°N, 76°54'W, elevation 290 m), the Russell E. Larson Agricultural Research Center at Rock Springs, PA (40°48'N, 77°52'W, elevation 365 m), and the USDA-NRCS National Plant Materials Center in Beltsville, MD (39°02'N, 76°56'W, elevation 36 m) during 2000 to 2002. Soil types were Unadilla silt loam (coarse-silty, mixed, active, mesic Typic Dystrudepts) at Big Flats, Hagerstown silt loam (fine, mixed, semiactive, mesic, Typic Hapludalfs) at Rock Springs, and Iuka sandy loam (coarse, loamy, siliceous, active, acid, thermic, Aquic Udifluvents) at Beltsville.
The Virginia wildrye accessions were collected by the USDA-NRCS plant materials centers from several northeastern states in 1998 and 1999 (Table 1). Thirteen accessions and two commercial sources (the cultivar Omaha from Stock Seed Co., Murdock, NE; and a Pennsylvania ecotype sold by Ernst Conservation Seeds of Meadville, PA) of wildrye were transplanted into single-row field plots during August 2000 at Beltsville and September 2000 at Rock Springs and Big Flats. Two orchardgrass cultivars (Potomac and Pennlate) were included for comparison. Seedlings of each entry were started in the greenhouse at the National Plant Materials Center, Beltsville. Entries were hand transplanted into single-row plots of 10 plants per plot. Each plot of 10 plants contained eight experimental plants and a border plant of wildrye at each end of the row. Border rows of Omaha wildrye alternated with row plots of the accessions. Plants were spaced 30 cm apart within rows, and rows were spaced 30 cm apart. At each location, a plastic weed barrier controlled weed seedlings during establishment. The plastic weed barrier was removed from all plots in March (Beltsville) or April 2001 (Big Flats and Rock Springs) after which weeds were controlled by hand and with herbicides.
Soil pH (to a 15-cm depth) was 5.7 at Big Flats, 6.5 at Rock Springs, and 6.1 at Beltsville. Soil P (determined by soil test on 0- to 15-cm deep soil samples) was above optimum at each location, whereas soil K was below optimum. Potassium fertilizer (0–0–60) was applied at 40 kg K ha–1 at each location in April 2001. Nitrogen (as ammonium nitrate) was applied at 56 kg ha–1 at green-up (late March or early April) in the spring and after the second harvest each year.
Plots were harvested on 22 May at Big Flats and 20 May at Rock Springs in 2001 and 2002. Harvests were on 26 April 2001 and 23 April 2002 at Beltsville. Relative maturity was determined visually on a 1 to 8 scale (Casler and Van Santen, 2000). Elymus accessions were at the late vegetative (leaf sheaths or stem internodes elongated to just before boot stage) developmental stage at all harvests, whereas orchardgrass was headed. Six experimental plants in each row were clipped to a 7-cm height, placed in cloth bags, and dried at 55°C for 48 h. The plot was discarded for yield purposes if fewer than four experimental plants were alive. At Rock Springs, plots in one block were severely damaged by the bluegrass billbug (Sphenophorus parvulus Gyllenhal); therefore, this block was discarded.
At the first harvest each year, 10 tillers of similar morphological developmental stage were taken from the experimental plants in each row. The number of leaves was counted on each tiller and the length and width of each fully elongated leaf blade was measured and leaf area calculated with a laser area meter (CID model CI-203, CID Devices Inc., Vancouver, WA). After measurements, the leaf blades and stems (including the leaf sheath) were dried at 55°C for 48 h, weighed, and the specific leaf area (SLA, cm2 leaf area g–1 leaf mass) and LSR calculated. Leaf length, width, and SLA data were presented in Sanderson et al. (2004).
Forage samples from the first harvest at each location were analyzed for nutritive value via calibrated near infrared reflectance spectroscopy by the Crop Quality Laboratory at the Pennsylvania State University. Calibration samples were analyzed for NDF, in vitro true digestibility (IVTD; 48 h fermentation) and CP by a commercial laboratory (DairyOne, Ithaca, NY). Detergent fiber and IVTD procedures were according to Van Soest and Robertson (1980). Digestible NDF was calculated from NDF and IVTD values. Nitrogen was determined by the Dumas combustion method (AOAC, 1990) and CP calculated as N x 6.25. Calibration statistics were: CP, standard error of prediction corrected for bias [SEP(C)], 7.4; R2, 0.99; NDF, SEP(C), 8.8; R2, 0.88; IVTD, SEP(C), 15.7; R2, 0.88.
The experiment was a randomized complete block design with four blocks at Big Flats and Beltsville and three blocks at Rock Springs. Plot means were used in the analysis of variance. A combined analysis across years and locations was done on all data. Years and locations were considered random effects and the accessions were considered fixed effects. The MIXED procedure in SAS (1998) was used to perform the analysis. Denominator degrees of freedom were calculated using the Satterthwaite option of MIXED analysis to determine appropriate degrees of freedom to test fixed effects and interactions of fixed effects. Planned contrasts were used to compare means. The contrasts were (i) average of Elymus entries vs. average of orchardgrass cultivars, (ii) average of New York accessions vs. average of Omaha and the commercial ecotype, (iii) average of Maryland accessions vs. average of Omaha and the commercial ecotype, (iv) the accession NJPMC vs. average of Omaha and the commercial ecotype, and (v) average of Vermont accessions vs. average of Omaha and the commercial ecotype. Spearman's rank correlations were used to examine changes in the relative performance of accessions and cultivars among years and locations. Pearson's product moment correlations were used to determine associations between nutritive value characteristics and morphological traits [leaf area, length, width, SLA, and LSR; reported in Sanderson et al., 2004]. Statistical significance was declared at the P < 0.05 level unless otherwise noted.
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RESULTS AND DISCUSSION
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Entry (accession or cultivar) x year interactions were significant for NDF, CP, and dNDF at Big Flats and Rock Springs, but not Beltsville. The interactions were an order of magnitude lower than the main effect of entry and were caused mainly by changes in magnitude of values between years and minor changes in rank among a few entries. Environmental interactions for nutritive value often are minor in evaluating perennial forages (Casler and Vogel, 1999) therefore we present nutritive value data as means across years within locations.
Significant differences were found between Elymus and orchardgrass and among the Elymus accessions for nutritive value (Tables 2, 3, and 4). Orchardgrass had higher concentrations of NDF and lower concentrations of CP and dNDF (except at Beltsville) than the Elymus entries. This was mainly because orchardgrass was more mature (inflorescence emergence to full peduncle emergence) at harvest then Elymus (sheath and internode elongation stages; data not shown).
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Table 2. Concentrations of neutral detergent fiber in Virginia wildrye accessions and two orchardgrass cultivars at three locations. Data are the least squares means of 2 yr at each location.
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Table 3. Concentrations of crude protein in Virginia wildrye accessions and two orchardgrass cultivars at three locations. Data are the least squares means of 2 yr at each location.
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Table 4. Concentrations of digestible neutral detergent fiber in Virginia wildrye accessions and two orchardgrass cultivars at three locations. Data are the least squares means of 2 yr at each location.
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Within Elymus accessions, the commercial ecotype and Omaha cultivar had higher NDF concentrations than the Elymus accessions from Maryland and Vermont (Table 2). The differences of Vermont accessions were due mainly to accession 9051779. The NJPMC accession had lower NDF than the commercial ecotype and Omaha cultivar at Big Flats and Rock Springs. The New Jersey and New York accessions generally had a greater CP concentration than the commercial ecotype and Omaha (Table 3). The Vermont accessions (due to 9051779) had greater CP than the Elymus checks at Big Flats and Beltsville but not at Rock Springs. Differences among accessions in dNDF were not as clear cut (Table 4). Consistent with results for NDF and CP, the NJPMC accession frequently had higher dNDF than the commercial ecotype or Omaha cultivar. The Vermont accessions (influenced mainly by accession 9051779) had higher dNDF than the commercial ecotype or cultivar at Big Flats and Beltsville. Spearman rank correlations among locations and years for NDF were highly positive and significant (Table 5). Crude protein concentrations at Rock Springs in 2002 were not significantly related to most other locations or years. Fewer than one-half of the Spearman rank correlations of dNDF were statistically significant.
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Table 5. Spearman rank correlation coefficients among locations and years for means of neutral detergent fiber, crude protein, and digestible neutral detergent fiber (n = 17).
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Some inconsistency in nutritive value data may have resulted from tillering differences among Elymus accessions and the orchardgrass cultivars. Some accessions produced fewer tillers in 2002 than in 2001, and the orchardgrass cultivars produced more tillers than Elymus (orchardgrass averaged 120 tillers per plant, whereas the Elymus accessions averaged 94 tillers per plant averaged across years; Sanderson et al., 2004). Concentrations of dNDF were not different between Elymus and orchardgrass at Beltsville perhaps because orchardgrass produced more vegetative tillers per plant than did Elymus (Sanderson et al., 2004), which may have affected relative nutritive value differences between species.
Differences in nutritive value among Elymus accessions were probably due to differences in plant morphology, specifically LSR (Table 6; Sanderson et al., 2004). Concentrations of NDF were negatively correlated with LSR in each year and each location, whereas CP and dNDF were positively correlated with LSR (except dNDF at Rock Springs in 2001; Table 7). Correlations of NDF with LSR ranged from –0.26 to –0.74 at Rock Springs. Correlations were of similar ranges for CP and dNDF with LSR. Thus, although Elymus accessions were estimated visually to be similar in maturity stage at each location, leaf and stem proportions differed enough to affect nutritive value. Grass leaves generally are lower in fiber and higher in digestibility than stems, thus a greater LSR should result in greater nutritive value. In other forage crops, such as alfalfa (Medicago sativa L.), selection for improved nutritive value altered LSR (Kephart et al., 1989).
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Table 6. Leaf-to-stem mass ratio in Virginia wildrye accessions and two orchardgrass cultivars at three locations. Data are the least squares means of 2 yr at each location.
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Table 7. Pearson correlation coefficients among nutritive value and leaf morphological attributes of Virginia wildrye accessions and orchardgrass cultivars at three locations during two years . Leaf area, length, width, and specific leaf area data were reported in Sanderson et al. (2004). There were 68 observations at each location and year except for Rock Springs in 2002 when there were 56.
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Neutral detergent fiber was positively correlated with leaf length at each location in each year (Table 7). Longer leaves probably required more structural tissue, which is lower in nutritive value. Leaf width was correlated with nutritive value constituents in only a few instances. At Big Flats, CP and dNDF were positively correlated with leaf width in 2001, whereas NDF was negatively correlated with leaf width in both years. Leaf width was negatively correlated with NDF at Beltsville and Rock Springs in 2001 and positively correlated with dNDF in both years at Beltsville. These correlations are consistent with the results of MacAdam and Mayland (2003) who found a negative correlation of leaf width with leaf tensile strength in tall fescue. They reasoned that wide leaves had a greater distance between veins and therefore more mesophyll tissue volume and less structural tissue than narrow leaves. Thus, wide leaves probably would have lower fiber concentrations and greater digestibility than narrow leaves. Leaf width was positively related to preference by grazing cattle (MacAdam and Mayland, 2003). In smooth bromegrasss, leaf width was positively associated with acid-pepsin dry matter disappearance (Sleper and Drolsom, 1974). The individual leaf attributes were inconsistently correlated with whole shoot nutritive value indicating that stem development may have controlled whole shoot nutritive value (Hacker and Minson, 1981).
Few other studies have compared nutritive value of Virginia wildrye to allow direct comparison with our results. In Alabama research, crude protein of Virginia wildrye ranged from 230 g kg–1 at the vegetative stage to 70 g kg–1 at the heading stage, whereas in vitro dry matter digestibility ranged from 800 to 600 g kg–1 for the same developmental stages (Bosworth et al., 1985). These values were similar to those for tall fescue (Festuca arundinacea Schreb.) in that study.
Crude protein and in vitro dry matter digestibility of Virginia wildrye were higher when grown under tree canopy than when grown in the open (210 vs. 170 g kg–1 and 700 vs. 640 g kg–1) in south Texas (East and Felker, 1993). Nitrogen concentration of Virginia wildrye ranged from 19 to 36 g kg–1 and in vitro organic matter digestibility ranged from 560 g kg–1 for fall regrowth to 630 g kg–1 for new spring vegetative growth in Alberta, Canada (Lawrence, 1978).
The nutritive value characteristics of Elymus in our study indicate that it is comparable to other cool-season grasses such as orchardgrass and tall fescue and would provide suitable forage for livestock. Our previous research, however, showed that Elymus lacked persistence and produced low yields and regrowth relative to commercially available orchardgrass cultivars (Sanderson et al., 2004). These traits would require improvement in Elymus to make it a suitable forage grass.
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CONCLUSIONS
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Virginia wildrye accessions differed in nutritive value principally because of differences in plant morphology. Leaf-to-stem mass ratio appeared to explain most of the variation in nutritive value among Virginia wildrye accessions. Neutral detergent fiber was negatively correlated with LSR, whereas CP and dNDF were positively related to LSR. Differences between Elymus and orchardgrass resulted from differences in maturity. Virginia wildrye is comparable to other cool-season grasses in nutritive value.
Received for publication December 5, 2003.
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ABSTRACT
INTRODUCTION
