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Species Interactions with Quackgrass and Their Effects on Forage Production

Dep. of Horticulture and Crop Science, The Ohio State Univ., 2021 Coffey Rd., Columbus, OH 43210

^* Corresponding author (Traci.Bultemeier{at}pioneer.com).

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
Quackgrass [Elytrigia repens (L.) Nevski] (QG) is a troublesome weed in row crop production but has some ideal forage characteristics for pastures. The competitive interactions of QG with other forage species under varying defoliation frequencies are not clearly understood. Our objective was to determine the competitiveness of QG with orchardgrass (Dactylis glomerata L.) (ORG) and/or white clover (Trifolium repens L.) (WC) under 2- or 6-wk cutting frequencies. Two replacement series experiments were conducted in a greenhouse between January and November 2002. Proportional mixtures (100:0, 33:66, 66:33, and 0:100) of QG:ORG and QG:WC, and a 33:33:33 mixture of all three species were established by planting tillers, rhizome shoots, or rooted stolons from ORG, QG, and WC, respectively. Results were similar across duplicate experiments so data were combined for the analysis. Yield for the 6-wk cutting frequency was almost twice that of the 2-wk cutting frequency (P 0.05). No yield differences (P > 0.05) were found among the QG:ORG mixtures at the 6-wk cuttings. A quadratic response (P 0.05) for the QG:WC mixtures under the 6-wk cutting frequency showed 23% greater yield from the two QG:WC mixtures than WC or QG monocultures. Yield of species mixtures did not differ significantly at the 2-wk cutting frequency. We concluded that QG was a productive forage species that yielded best when grown with a complementary species (i.e., WC) rather than with a species likely to compete directly for the same resources (i.e., ORG).

Abbreviations: ORG, orchardgrass • QG, quackgrass • WC, white clover

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
QUACKGRASS is a weedy perennial grass that is difficult to control, has the capacity to spread rapidly, and has negative effects on row crop yield. Quackgrass is considered one of the three most serious weeds in the world, reported to infest 37 different crops in 65 countries (Reidy and Swanton, 2001). Despite its classification as a weed, quackgrass has characteristics including erect stem growth habit, high feed quality, vegetative reproduction via rhizomes, adaptation to a wide range of soil fertility, and long periods of seasonal growth that make it an acceptable species for forage production (Smith, 1973; Marten and Hoven, 1980; Malzer and Schoper, 1984; Greub et al., 1986; Christen et al., 1990; Sheaffer et al., 1990; Tardiff and Leroux, 1992; Bultemeier et al., 2002a, 2002b, 2003). Results from recent studies suggest that producers can take advantage of quackgrass when it is present in grasslands, as it represents a serious weed problem only when rotating fields to other crops (Christen et al., 1990).

One aspect of uncertainty in the literature is the influence of defoliation on the ability of quackgrass to compete with other forage species. In the work reported here, we utilized a replacement series experiment to study interspecific competition and compare the performance of quackgrass (target species) across a range of selected species mixtures (Connolly et al., 2001). As defined by deWit (1960), a replacement series experiment consists of a pure stand of each of the constituent species and a range of mixtures in which one species is sown at proportion p of its pure-stand density and the other species is sown at proportion 1– p of its pure-stand density. The proportions of species are varied while maintaining a constant total plant density. When plant scientists use the replacement series design, the objectives of the study usually involve determining how one species affects another's performance (Connolly et al., 2001).

Orchardgrass and white clover are common species in pastures in Ohio and are common companion species for quackgrass. Orchardgrass and white clover have contrasting growth patterns and we hypothesized that orchardgrass, a bunchgrass, might be more competitive against quackgrass than the stoloniferous legume, white clover.

Defoliation has distinct and pronounced effects on grassland production and the interactions between species (Brougham 1970). Quackgrass has been shown productive in monocultures and mixed pastures under 5-cm cutting with regrowth periods of 1 mo or greater (Malzer and Schoper, 1984; Casler and Goodwin, 1998; Griffin et al., 2002). Carlassare and Karsten (2002) found in mixed swards, that quackgrass was more productive when grazed to 7-cm height (on average every 29 d) than when grazed to 5-cm height (on average every 24 d). The effect of defoliation frequency on quackgrass is unknown, as is the potential for controlling quackgrass by close defoliation.

The objective of this study was to compare the performance of QG growing with either ORG or WC, under two cutting frequencies.

	MATERIALS AND METHODS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
Two replacement-series experiments were conducted 2 Jan. to 31 May 2002, and 5 June to 17 Oct. 2002 in a greenhouse at The Ohio State University, Columbus, OH. Plants in each experiment were grown for 19 wk in pots that were 47 cm long, 35 cm wide, and 15 cm deep. There were eight species mixtures, each harvested at either 2- or 6-wk cutting frequencies.

Plant Collection, Planting Procedure, and Growing Conditions
Approximately 1 m² of quackgrass-dominated sod was collected to 15-cm depth from a 4-yr-old alfalfa field in Holmes County, OH (40°25'N, 81°40'W). Similarly, sod of ‘Jumbo’ ladino white clover was collected from a 1-yr-old, rotationally grazed pasture in Knox County, OH (40°15'N, 82°25'W), and sod of ‘Haymate’ orchardgrass was collected from a 5-yr-old pasture in Franklin County, OH, (40°8'N, 83°5'W) that had been mechanically harvested five times per year. Sod was collected September–October 2001 and given an adaptation period in the greenhouse until 2 Jan. 2002.

Species mixtures were established by hand-transplanting QG, ORG, and WC from the field-harvest sod on 2 Jan. 2002 into pots filled with approximately 24.5 kg of soil. The soil mixture comprised 500 g kg^–1 Crosby silt loam (mesic Aeric Epiaqualfs), 250 g kg^–1 sand, and 250 g kg^–1 peat. Tillers (with roots) were separated from ORG plants and QG rhizomes were cut between nodes that had sprouted shoots and roots. WC stolons were separated from the mother plant, taking care that roots were present on at least two of the nodes. Gibberellic acid, a rooting hormone, was applied to the cut end of each WC stolon to promote root growth and plant survival. A total of 60 plant propagules were planted per pot (365 plants m^–2), with QG rhizome nodes, ORG tillers, and WC stolon nodes considered as propagules.

There were eight species mixtures, comprising QG:ORG or QG:WC in proportions of 0:100, 33:66, 66:33, and 100:0, as well as a mixture with equal proportions of QG, ORG, and WC (33:33:33). Approximately 15% of the plants died and were replaced within 2 wk following initial establishment. In Exp. 1, QG was planted 2 wk before the other two species to encourage satisfactory establishment; however, in Exp. 2, this was considered unnecessary and all species were planted at the same time. Throughout the study, pots received daily watering and weekly applications of fertilizer solution [comprised of 0.5 M Ca(NO₃)₂ 4 H₂0, 0.3 M KH₂PO₄, 0.5 M KNO₃, 0.3 M NH₄NO₃, 0.25 M MgSO₄ 7 H₂O, and 5 mM Fe, pH 6.5] (J.R. Peters, Inc., Allentown, PA). Artificial lights were used during winter and autumn months to provide at least 14 h of light. Temperature was maintained at 24 to 27°C during the day and 18 to 21°C at night.

During a 7 wk establishment period, the top 5 cm was cut off the forage in all pots twice monthly to adapt the plants to a regular cutting regime. At the 8th week, all pots were harvested to 2.5 cm above soil level. Throughout both experiments, the cutting regimes ensured grasses remained in a vegetative state; however, some flowering did occur for white clover.

Plant Measurements
Pot yield was measured beginning at the 8th week after establishment, and every 2 or 6 wk for 12 wk, from the total sample that was cut to 2.5 cm above soil level, then dried 48 h at 55°C. Although not specifically measured, vegetation was 15 to 25 cm in height at harvesting. Pot yield was determined at each harvest of the 2- and 6-wk treatments. The reported yield was the total harvested over the 12-wk measurement period (six harvests from the 2-wk cutting and two harvests from the 6-wk cutting). Botanical composition was determined for each pot from a subsample from the harvested vegetation. The sample was thoroughly mixed and three to four small "grab" samples were combined into the subsample that was subsequently separated into component species by hand. These fractions being smaller were dried 24 h at 55°C. Subsample weight was added back to the sample weight to calculate total yield for each pot. Residual yield, below 2.5 cm, was determined by cutting residual forage from a 10- by 10-cm area of each pot to ground-level and drying 48 h at 55°C. Botanical composition and residual yield did not change very rapidly and were measured each 6 wk, when the harvests of 2- and 6-wk treatments coincided.

The density of tillers (grasses) or growing points (white clover) was determined at the completion of each experiment from counts of tillers or growing points for each species within two 10- by 10-cm quadrats per pot.

Root and rhizome mass were determined from two 10- by 10-cm sections of soil that were removed from each pot. Roots of the three species could not be distinguished and were combined to determine total root mass. Large roots were manually removed from the soil, and the remaining sample was washed and screened through a 12/64-mesh screen to retrieve the fine roots. Large and fine roots were subsequently combined. Rhizomes were only present in treatments that included quackgrass, and were manually separated from roots. Rhizomes and roots were dried 48 h at 55°C.

Statistical Analysis
Both experiments were conducted as a randomized complete block design with three replicates. Treatments within each complete block were a factorial arrangement of eight species mixtures and two cutting frequencies (Table 1). Replacement series responses (e.g., linear and quadratic effects for 0, 33, 66, and 100% composition) were analyzed by single-degree-of-freedom contrasts using the General Linear Model (GLM) procedure of SAS (SAS for Windows Release 8.2, SAS Institute Inc., Cary, NC). Since there were 16 treatments (Table 1) only 15 contrasts of interest were tested (Table 2).

	RESULTS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
On average across the species mixtures, yield was 43 to 58% greater for 6-wk cutting than for the 2-wk cutting (Table 3, Fig. 1a) . A significant QG:WC x cutting interaction for the quadratic response (P < 0.05, Table 3) was the result of higher yield for the two WC mixtures (33 and 66 QG:WC) than either monoculture for 6-wk cutting (Fig. 1a), which did not occur for 2-wk cutting. There were no differences in yield among species mixtures under the 2-wk cutting frequency (Fig. 1a, Table 3).

View larger version (21K): [in this window] [in a new window]   Fig. 1. Total yield (A), quackgrass rhizome mass (B), and total root mass (C) for proportional mixtures of quackgrass (QG) and orchardgrass (ORG), or QG and white clover (WC), under 2-wk and 6-wk cutting. Symbols are means of 6 observations (3 replicates and 2 experiments); the analysis of variance is given in Table 3.

View larger version (26K): [in this window] [in a new window]   Fig. 2. The effect of number of species planted on yield (g m–2), and rhizome and roots mass (g m–2) of 8 mixtures of quackgrass (QG) and orchardgrass (ORG) and/or white clover (WC) at 2-wk or 6-wk cutting. Symbols are means of 6 observations (3 replicates and 2 experiments); *, significance of regression P 0.05.

On average for all treatments, the total tiller density of grasses and growing-point density of white clover (number m^–2) increased by 7.4 to 19.9 times during the experiment (Table 1). Contrasts determined that there was a significant linear effect on total tiller and growing-point density for QG:WC at the 6-wk cutting frequency (Table 3), but no significant effect for QG:ORG. Responses among species were similar for the 6- and 2-wk cutting frequencies, and averaged 12.7-fold and 12.6-fold, respectively. On average for the QG:ORG and QG:WC mixtures, there was a greater increase in the total tiller and growing point density when the proportion initially planted was 33% (14.2 times) than when the proportion initially planted was either 66 or 100% (9.5 and 12.9 times, respectively) (Table 1).

Quackgrass rhizome mass was significantly greater for 6- than 2-wk cutting (Table 3, Fig. 1b). In mixtures with both WC and ORG, QG rhizome mass increased linearly with increasing proportion of QG (Fig. 1b). Rhizome mass was negatively related to the number of species planted and the slope of the relationship was greater for 6-wk cutting than 2-wk cutting (Figs 2b and 2e).

Mean root mass was 2.5 times greater under 6-wk cutting than 2-wk cutting (Table 3, Fig. 1). For the species mixtures, a significant linear contrast for QG-ORG under 6-wk cutting (P < 0.05, Table 3) and greater root mass for ORG than QG monocultures (409 vs. 153 g m^–2, respectively, Fig 1c) showed linear replacement of ORG roots with QG roots with an increasing proportion of QG. Root mass for the QG and WC monocultures were similar (133 vs. 153 g m^–2, respectively). Root mass was poorly related to the number of species planted (Fig. 2c and 2f).

	DISCUSSION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
Species Effects
Results of this study showed that quackgrass was a complementary species able to coexist with both white clover and orchardgrass. Casler and Goodwin (1999) have previously reported the compatibility of quackgrass and white clover in Wisconsin. Under infrequent (6 wk) and close (2.5 cm) cutting in mixtures, quackgrass yield response was similar to companion species such as white clover and/or orchardgrass. We observed no synergistic yield responses for mixtures of orchardgrass and quackgrass, and it was likely in our experimental conditions that these species competed equally for the available resources. Since water and nutrients were applied in nonlimiting amounts, the yield-limiting resource was probably light. Both these species had a similar, erectophyllous canopy structure (Anten and Hirose, 1999) with the result that when they were planted in a substitutive replacement series, there was no apparent advantage in light interception (or yield) from the mixtures. Although quackgrass was rhizomatous (unlike orchardgrass), this trait was unlikely to have resulted in any advantage in our experiment since the dense and uniform planting in our study minimized any opportunity for quackgrass to spread within the pots. In field conditions, the rhizomatous habit might allow invasion and spread into favorable niches, such as where other vegetation was absent. The contrasting underground morphology of these grass species, i.e., the rhizomes of quackgrass (Fig. 1b) and the prolific root mass of orchardgrass (Fig. 1c), would be interesting to explore for future experimentation with soil-limiting resources (nutrients and water). Chemical composition was not measured in this study; however, quackgrass is also reported to have good protein content for livestock production (Malzer and Schoper, 1984).

Of particular interest was the increase in total yield when quackgrass and white clover were planted together in mixtures (Fig. 1a). Yield results showed a significant contrast in the QG:WC x cutting interaction and in the quadratic response of QG:WC at the 6-wk cutting frequency, indicating the positive response when planting white clover and quackgrass together. The erectophyllous canopy structure of grasses allows deeper penetration of light into the canopy than the planophyllous canopy of white clover (Anten and Hirose, 1999), probably resulting in the potential for better light utilization and yield from grass-clover mixtures in our study. The absence of this response at the 2-wk cutting frequency, where plants were prevented from complete canopy development, was further evidence that the response was mediated through light interception.

The quackgrass used in this study was transplanted from plants that had invaded an alfalfa pasture in central Ohio. This plant material had not been subjected to the extent of selection for production and persistence as had the orchardgrass and white clover. Variation in leaf morphology (length and width) among quackgrass plants was observed. No attempt was made to quantify this variation or its effect on yield, although the planting procedure ensured the variation was distributed among the experimental pots. Morphologically uniform research populations do occur and in yield trials show large genotype x environment interactions (Casler and Goodwin, 1998). Apparently the natural selection that likely occurred for our experimental material had resulted in a population that was productive under our experimental conditions.

Results from this study (Fig. 2) support the hypothesis that increases in species richness are related to increased forage production (Barker et al., 2003). Although only for one to three species, the positive relationship between species number and yield in this study, was consistent for similar relationships involving up to 12 species (Barker et al., 2003). Presumably the contrasting characteristics of each species such as, differences in height and vegetative growth allowed complementary use of the available light, space, and nutrients. Quackgrass appears to be a useful addition to the biodiversity of swards for forage production.

Cutting Effects
Cutting frequency had a significant effect on yield (Fig. 2a and 2d) with the 6-wk cutting frequency having almost twice the yield of the 2-wk cutting frequency. This was consistent with studies by Brougham (1970), Sheaffer et al. (1990), and Hume (1991), who determined that cutting frequency had the greatest effect on growth rates, confirming general recommendations of long intervals between defoliations to achieve high yields for vegetative grasses. The reduced yield of 2-wk cutting, combined with the close cutting height (2.5 cm), shows we achieved significant defoliation stress, but were unable to reduce the relative performance of quackgrass. Carlassare and Karsten (2002) found reduced quackgrass production under close (5 cm) and frequent defoliation (average rest period of 24 d); however, the result of this study suggests that closer and more frequent defoliation is unlikely to remove quackgrass from mixtures.

The 2.5-cm cutting height used in this study apparently benefited quackgrass, with an average contribution to yield of 74% compared with equal contributions from the other two species. Most reported field studies using a 5-cm cutting height found good production from quackgrass (e.g., 17% for Carlassare and Karsten 2002, 14% for Griffin et al., 2002), but rarely that it achieved the contribution observed in this study. It is possible that the rhizomes afforded quackgrass an advantage compared with orchardgrass or white clover at the 2.5-cm cutting; however, specific investigation of cutting height effects would be necessary to determine if this were the case.

A negative effect of close and frequent defoliation on root growth and development was reported by Thornton (1996) who found that increased severity of defoliation resulted in decreased root mass per unit root weight in Festuca rubra L., Lolium perenne L., Poa trivialis L., and Agrostis castellana Boiss. & Rueter. This was consistent with the results from this study that showed both root and rhizome dry weight decreased with more frequent clipping (Fig. 1b and 1c). Almost certainly, the 2-wk cutting prevented the translocation of sufficient energy belowground to support root and rhizome growth.

	CONCLUSIONS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
Two replacement series experiments were conducted in a greenhouse with the objective to compare the performance of quackgrass growing with either orchardgrass or white clover, under 2- and 6-wk cutting. Quackgrass was a complementary species able to coexist with both white clover and orchardgrass; however, yield was greater when it was planted with white clover, or both white clover and orchardgrass. The 2-wk cutting frequency reduced total yield, but did not affect the relativity between the species. Close (2.5 cm) and frequent (2 wk) defoliation seem unlikely to control quackgrass in mixed pastures. Quackgrass appears to be a useful species to increase the biodiversity of swards for forage production.

	ACKNOWLEDGMENTS

 
The authors are grateful to Ms. Megan Burgess and Mr. Keith Diedrick for their assistance with planting and harvesting and to Dr. Steven St. Martin for statistical advice. We also thank Mr. Terry Lester, Mr. and Mrs. Ronald Brenly, and Mr. John McCormick for allowing us to use plants from their production fields. Partial funding for this project was provided by the Ohio Agricultural and Research Development Center (OARDC) Graduate Fund.

	NOTES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
Salaries and research support provided in part by state and federal funds appropriated to the Ohio Agricultural Research and Development Center, The Ohio State Univ. Manuscript Number HCS 02-46.

Received for publication May 23, 2003.

	REFERENCES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 

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• Bultemeier, T.L., D.J. Barker, R.M. Sulc, S.K. Harrison, and E.E. Regnier. 2002b. Quackgrass interactions and effects on forage species. North Central Weed Sci. Soc. Abstr. 199. [CD-ROM Computer File]. North Central Weed Sci. Soc., Champaign, IL.
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This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via ISI Web of Science (1) Citing Articles via Google Scholar Google Scholar Articles by Brenly-Bultemeier, T. L. Articles by Regnier, E. E. Search for Related Content PubMed Articles by Brenly-Bultemeier, T. L. Articles by Regnier, E. E. Agricola Articles by Brenly-Bultemeier, T. L. Articles by Regnier, E. E. Related Collections Forage Management Crop Cytology