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a Alcalde Sustainable Agric. Sci. Ctr., New Mexico State Univ., P.O. Box 159, Alcalde, NM 87511 USA
b Tucumcari Agric. Sci. Ctr., New Mexico State Univ., 6502 Quay Road AM.5, Tucumcari, NM 88401 USA
lmlaur{at}nmsu.edu
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ABSTRACT |
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 TOPNOTES ABSTRACT INTRODUCTIONMaterials and methodsResults and discussionConclusionsREFERENCES |
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Abbreviations: MONO, tall fescue monoculture • AG/TF, `Alfagraze' alfalfa mixed with tall fescue • WI/TF, `Wilson' alfalfa mixed with tall fescue • ALF/TF, mean of alfalfa cultivars mixed with tall fescue • BFT/TF, birdsfoot trefoil mixed with tall fescue • CM/TF, cicer milkvetch mixed with tall fescue • KC/TF, kura clover mixed with tall fescue • MIX, mean of mixtures • PLS, pure live seed
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INTRODUCTION |
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TOPNOTESABSTRACTINTRODUCTIONMaterials and methodsResults and discussionConclusionsREFERENCES |
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Alfalfa is well adapted (Tapia and Lugg, 1986) to most of the semiarid West when provided with adequate moisture, and provides both high yields and quality (Karnezos et al., 1994) as well as fixing 82 to 254 kg N ha-1 yr-1 (Heichel and Henjum, 1991). Many producers have incorporated this species into their irrigated cool-season grass pastures, grazing them during the spring and fall and harvesting 1 to 2 cuttings of hay during the summer to use as supplemental winter feed. However, there are some limitations to alfalfa's sustainability in regard to increased inputs to prevent bloat (Karnezos et al., 1994; Majak et al., 1995; Marten et al., 1990; Peterson et al., 1992), historically poor persistence under grazing (van Keuren and Matches, 1988), reestablishment only by seeding, and autotoxicity in reestablishment (Melton et al., 1988). For these reasons, interest in alternative forage legumes is building and, while several have been shown to be well adapted to the higher precipitation areas of the eastern USA (Heichel and Henjum, 1991; Hoveland and Richardson, 1992; Taylor and Smith, 1998) and to the drier but cooler climates of the central and northern Great Plains and Rocky Mountains of the USA and Canada (Berg, 1990; Farnham and George, 1994; Hoveland and Richardson, 1992; Kephart et al., 1990; MacAdam et al., 1998; Majak et al., 1995; Marten et al., 1990; Townsend, 1993), little is known about their adaptability to the southern Rockies (Tapia and Lugg, 1986).
Of these legumes, birdsfoot trefoil and cicer milkvetch yield inconsistently compared to alfalfa (Berg, 1990; Kephart et al., 1990; Loeppky et al., 1996; Peterson et al., 1992) but produce more of their season total later when the cool-season grass growth is reduced by high temperatures (Hoveland and Richardson, 1992; Loeppky et al., 1996). The quality of these forages is also variable compared with alfalfa (Danso et al., 1991; Kephart et al., 1990; Marten et al., 1990); but, they are nonbloating (Majak et al., 1995) and have the ability to persist under grazing and avoid environmental extremes (Peterson et al., 1992, 1994) by self-seeding without any autotoxicity in the case of birdsfoot trefoil (Danso et al., 1991; Mallarino et al., 1990) or by rhizomes for cicer milkvetch (Kephart et al., 1990). Kura clover, another legume that has been used successfully from the north-central USA to Kentucky (Taylor and Smith, 1998), is rhizomatous (Sheaffer et al., 1992; Taylor and Smith, 1998), yields more consistently like alfalfa (Peterson et al., 1994), and is of generally higher quality than alfalfa in that nearly the entire sward consists of leaves, flowers, and petioles (Peterson et al., 1994; Taylor and Smith, 1998). However, like alfalfa, it also causes bloat (Taylor and Smith, 1998), a problem that can be effectively managed with poloxalene (Karnezos et al., 1994; Taylor and Smith, 1998), or possibly by including it in a mixture where the grass component is >50% (Ball et al., 1991; Sheaffer et al., 1992; Taylor and Smith, 1998). Cicer milkvetch has been found to cause photosensitization in white-haired animals (Marten et al., 1990) but the incidence of occurrence may also be reduced by including grass in the sward. A limitation of all these alternative legumes is slow establishment (Danso et al., 1991; Loeppky et al., 1996), but good stands can be achieved by the second or third year with adequate moisture and good management (Farnham and George, 1994; Marten et al., 1990; Sheaffer et al., 1992; Townsend, 1993; Townsend et al., 1990). Another limitation is lower dinitrogen fixation, particularly with birdsfoot trefoil, which fixes only 60 to 138 kg N ha-1 yr-1 (Farnham and George, 1994; Mallarino et al., 1990). That is not enough to maximize cool-season grass growth (Hoveland and Richardson, 1992).
Finally, response in mixtures with cool-season grasses has been variable. MacAdam et al. (1998) and Hoveland and Richardson (1992) increased summer productivity of tall fescue by including birdsfoot trefoil in the sward, but there was no such effect when that legume was sown with orchardgrass (Dactylis glomerata L.) (Farnham and George, 1994; MacAdam et al., 1998). Townsend (1993) reviewed several authors who reported decreased dry matter yields and beef production when cicer milkvetch was added to grass pastures. Part of the variability in performance of the alternative legumes in mixtures is due to competition between the components of the mixtures (Farnham and George, 1994; Loeppky et al., 1996; Taylor and Smith, 1998; Townsend, 1993; Townsend et al., 1990), which may be enhanced by differences in local adaptation between the components as well as by the management imposed. There is little information about either the performance of kura clover in binary mixtures with cool-season grasses or its adaptability to the semiarid West.
The objective of this research is to compare dry matter yields and changes in stand composition of these alternative forage legumes and alfalfa in mixtures with tall fescue under a three-cut management system in the steppe of the southern Rocky Mountains.
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Materials and methods |
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TOPNOTESABSTRACTINTRODUCTIONMaterials and methodsResults and discussionConclusionsREFERENCES |
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Initial soil test results from the surface 15 cm indicated low levels of NaCHO3-extracted P (28.5 kg ha-1), moderate levels of K (1:5 H2O extract) (63 kg ha-1), and a pH of 7.4. In the spring of each production year (1994–1997), the site received 49 kg P ha-1 as granular 0–46–0. Additionally, every year MONO received 134 kg N ha-1 as 46–0–0 dissolved in water and applied in three equal split applications, each approximately 1 mo before an anticipated harvest. Plots were irrigated during the growing season to supplement precipitation. For all irrigations, water was applied until the presence of moisture was observed at the center of the top of all beds for their full length. A flowmeter was used to estimate irrigation amounts as approximately 13 cm per application.
The study was managed under a three-cut management system with harvests taken mid-May and mid-September to simulate grazing and mid-July as a hay cutting. In May 1994, the tall fescue was fully headed, and in the remaining years it was in the boot stage. It was always vegetative in July and September. The alfalfa was in bud stage in May and >25% bloom in July and September. Birdsfoot trefoil, cicer milkvetch, and kura clover showed no evidence of reproductive growth until the July harvest, and reproductive growth continued through the September cutting. For each harvest, two 0.836 m2 quadrats were hand-clipped from each plot, leaving about 5-cm stubble. Placement of the square quadrats was such that a representative cross-section of the furrow-bed continuum was obtained in each subsample. The area of the subsample thus included two seeded rows of the legume and two of the tall fescue. The corners of the sampling locations were staked so that samples were always collected from the same locations in the plots for the duration of the study. For mixtures, each entire subsample was separated by species during clipping. Each species was placed in a separate bag and dried for 48 h at 65°C to determine DM yield of each component species within the subsample. Combined DM yield of each subsample was calculated as the sum of the components and percent grass in the sward was calculated by dividing the grass DM by the combined DM. After each harvest, the entire plot was clipped to approximately 5 cm and the residue removed.
The study was analyzed as a split-split plot where Treatment (MONO vs. MIX) was the whole plot, species within treatment (Within MIX) was the subplot, and cultivar within species (variety within ALF/TF) was the sub-subplot. Data for percent grass in the sward, DM yield of component species, and combined DM yield were subjected to analysis of variance and SAS GLM techniques (SAS Inst., 1996) for within-harvest comparisons and repeated measurements comparing Harvest x Treatment for each year and Year x Treatment during the 4 yr of the study (Snedecor and Cochran, 1980). Protected (P 
0.05) nonorthogonal contrasts were used to determine where differences occurred between species within MIX.
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Results and discussion |
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TOPNOTESABSTRACTINTRODUCTIONMaterials and methodsResults and discussionConclusionsREFERENCES |
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No data were collected in the seeding year (1993). Differences between cultivars within ALF/TF were few and not deemed meaningful; therefore, they were combined for purposes of analysis and reporting. Data for percent grass in the sward, grass DM yield, legume DM yield, and combined DM yield are presented in Fig. 1 to 4
. All differences reported here are significant at the level of P 0.05.
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Throughout the study, grass DM yield (Fig. 2) of MONO was higher than that measured by Danso et al. (1991). Legume DM yields (Fig. 3) were similar to those measured in a previous study at this location (Tapia and Lugg, 1986), and more comparable to those measured by Danso et al. (1991) than the grass DM yields. MONO and MIX were not different in grass DM yield harvested in May of any year, but MONO produced more grass DM than MIX in all July and September cuttings (Fig. 2). Grass–legume competition in MIX may have been a factor. From 1994 to 1996, the tall fescue in MIX produced a higher percentage of its total DM in May, while the legumes yielded a higher percentage of their total DM in one or both of the later harvests in each of those years (Fig. 2 and 3). This seasonal distribution of legume yield is similar to the observations of Hoveland and Richardson (1992) and Loeppky et al. (1996) regarding birdsfoot trefoil and cicer milkvetch. Note, however, that KC/TF produced its highest tall fescue DM and legume DM in May in 1996 and 1997 and yields of both grass (Fig. 2) and legume (Fig. 3) declined across both of those seasons. It may be that the root system of the kura clover was established well enough by 1996 to compete with the tall fescue for nutrients and water in all cuttings, but was still putting most assimilate into root development or carbohydrate storage rather than topgrowth during the latter part of the growing season. The Year x Treatment effect of MONO vs. MIX for grass DM yield was not significant (Fig. 2); however, a change in the competitive advantage of the legumes occurs in the 1996 and 1997 growing seasons such that the legumes competed differently with the tall fescue as demonstrated by a significant Year x Treatment effect within MIX for legume DM yield (Fig. 3). Nonorthogonal contrasts between treatments within MIX indicate that the alfalfa becomes less productive and the DM yields of the alternative legumes continue to increase at differing rates leading to significant linear and quadratic effects of Year x Treatment for legume DM (Fig. 3).
Combined dry matter yields of the mixtures included in this study (Fig. 4) are consistent with those of other studies (Farnham and George, 1994; Hoveland and Richardson, 1992; Townsend et al., 1990). In 1994, there was no difference between MONO and MIX in combined DM yield for any cutting, although MONO had numerically higher yields than MIX. This is most likely because of the slow establishment rate of all legumes except alfalfa. Since MONO received N fertilizer it could produce more grass DM yield than MIX (Fig. 2), which was unfertilized. For N fertilization of grass–legume mixtures, Cameron et al. (1990) found that N fertilization did not affect alfalfa establishment or yield but did reduce populations slightly in the third and fourth years, whereas Hoveland and Richardson (1992) showed that N fertilization reduced the contribution of birdsfoot trefoil in most harvests. Applying N to the mixtures would have given an advantage to the tall fescue during establishment, causing too much competition for the birdsfoot trefoil, cicer milkvetch, and kura clover in the mixtures as these legumes are slow to establish (Farnham and George, 1994; Sheaffer et al., 1992; Taylor and Smith, 1998; Townsend, 1993). Once the legumes reached their competitive potential, legume DM contributed more to the combined yield of MIX and grass DM contributed less, at least until September 1996 as indicated by percent grass in the sward (Fig. 1). During the life of the study, MIX yielded nearly 10 Mg ha-1 more combined DM yield than MONO (Table 1) . This is typical of that demonstrated by other researchers (Hoveland and Richardson, 1992; Townsend et al., 1990).
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In this study, yields of CM/TF equilibrated to those of MONO, indicating that the cicer milkvetch is contributing enough N to replace the fertilizer requirement of the tall fescue. However, that may not be sufficient to warrant its use, especially in light of the performance of the other species tested. Swards of BFT/TF and KC/TF continued to increase throughout the study achieving total annual combined yields of >11 Mg ha-1 and equaling the yields of ALF/TF as it declined in 1997 (Fig. 4). The difference between these two mixtures lies in the species composition, in that the contribution by birdsfoot trefoil appears to have plateaued at about 6.5 Mg ha-1, with the increase in combined yield in 1997 associated with an increase in tall fescue yield. The kura clover, on the other hand, continued to increase in yield, apparently at the expense of the tall fescue, since the percent and DM yield of tall fescue in the sward both continued to decline in that mixture from 1996 to 1997 (Fig. 1 and 2). Taylor and Smith (1998) noted that kura clover did not compete well with tall fescue suggesting that the kura clover be allowed to establish before planting the tall fescue. Planting in alternate rows (Townsend et al., 1990) or drilling the grass in rows and broadcasting the kura clover (Hoveland and Richardson, 1992) may be a viable option for same-operation seeding.
Although ALF/TF had higher cumulative combined DM yield than the other species in the study (Fig. 4), BFT/TF and KC/TF may eventually be equal to or greater than ALF/TF in sustained yields and thus total yield over the life of the original seeding. However, since the grass percent of KC/TF was <50%, animals grazing mixtures including kura clover at those grass compositions would need to be supplemented with a bloat preventative (Ball et al., 1991; Karnezos et al., 1994; Taylor and Smith, 1998), while this would not be the case with BFT/TF because birdsfoot trefoil is nonbloating.
The harvest management used in this study is typical of that used elsewhere (Cameron et al., 1990; Danso et al., 1991; Farnham and George, 1994; Kephart et al., 1990; Peterson et al., 1992; Townsend et al., 1990). In a more intensive harvest regime, the alfalfa may yield more, and both the birdsfoot trefoil and kura clover may decline; however, all of these species can perform well under rotational grazing when properly managed.
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Conclusions |
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TOPNOTESABSTRACTINTRODUCTIONMaterials and methodsResults and discussionConclusionsREFERENCES |
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ACKNOWLEDGMENTS |
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NOTES |
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TOPNOTESABSTRACTINTRODUCTIONMaterials and methodsResults and discussionConclusionsREFERENCES |
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Received for publication November 30, 1998.
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TOPNOTESABSTRACTINTRODUCTIONMaterials and methodsResults and discussionConclusionsREFERENCES |
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