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Performance of irrigated tall fescue-legume communities under two grazing frequencies in the southern Rocky Mountains, USA.

RECENTLY, there has been increased interest in maximizing utilization of irrigated pastures in the western USA because of changes in federal land policies on public grazing lands and the desire to reduce costs by using animals for harvesting (Asay et al., 2001; Guldan et al., 2000; Waldron et al., 2002). Many producers prefer monoculture grass pastures because they are easier to manage (Beuselinck et al., 1994; Clark, 2001). Maximum production by cool-season pasture grasses in the West is nearly impossible without irrigation (Waldron et al., 2002), but tall fescue is a high yielding perennial cool-season grass (Leep et al., 2002; Waldron et al., 2002) that is among the most stable in maintaining yield across varied irrigation levels (Lauriault et al., 2005b: Waldron et al., 2002). Lack of uniform seasonal yield distribution has been a problem in budgeting forage resources to meet animal demands when using monoculture grasses (Hermann et al., 2002; Leep et al., 2002; Sleugh et al., 2000). Additionally, pastures containing monocultures are more susceptible to environmental stress than mixtures (Harmoney et al., 2001; Tracy and Sanderson, 2004a), often allowing encroachment by less productive weedy species (Clark, 2001).

Grasses that yield well as monocultures also generally perform well in mixtures with other grasses and legumes (Haynes, 1980; Leep et al., 2002). Mixing grasses increases species diversity, helping to overcome environmental stress and prevent weed encroachment. Mixing grasses often also increases yield, but this does not always lead to higher animal productivity (Clark, 2001; Tracy and Sanderson, 2004b). Inclusion of legumes improves seasonal yield distribution of perennial cool-season grass pastures (Hermann et al., 2002; Lauriault et al., 2005a: Leep et al., 2002) as well as overall yield and quality (Sleugh et al., 2000: Tracy and Sanderson, 2004b), which does lead to greater animal productivity (Lauriault et al., 2005a). Maintaining a sustainable balance between the grass and legume components becomes a management goal (Barker et al., 2002; Clark, 2001; Edwards et al., 1996) that is often difficult to attain (Harris et al., 1999) because of lack of persistence, which has been a limitation for forage legumes (Beuselinck et al., 1994) because of grazing and other environmental factors (Harmoney et al., 2001; Harris et al., 1999).

Acceptable levels of legume persistence are dependent on species compatibility, growth habit, ecosystem, and management (Casler, 1988; Beuselinck et al., 1994: Tracy and Sanderson, 2004a). All legumes have limitations (Leep et al., 2002), so it is likely that only one or two species can maximize productivity in a given environment (Beuselinck et al., 1994; Skinner et al., 2004), especially in productive sites (Harmoney et al., 2001) under grazing (Leep et al., 2002). Even when more complex pastures mixtures are sown, the number of persistent species often declines within a few seasons (Skinner et al., 2004: Tracy and Sanderson, 2004b; Wedin et al., 1965). Alfalfa has been the legume of choice in most of the USA (Haynes, 1980), but bloat is a concern in addition to stand longevity (Guldan et al., 2000; Lauriault et al., 2005a; Rumburg, 1978). Research on pasture legumes other than alfalfa has not been widely done, however, especially in the southern Rocky Mountains (Leep et al., 2002).

Guldan et al. (2000), in the irrigated steppe of the southern Rocky Mountains, described legumes that have potential as alternatives to alfalfa in binary mixtures with tall rescue. Lauriault et al. (2003) reported the value of those mixtures under long-term hay management. Many forage species respond differently to grazing than to hay harvest (Beuselinck et al., 1994; Sanderson et al., 2004). Hay management differs from grazing in selectivity (Edwards et al., 1996) and is typically less frequent in defoliation (Beuselinck et al., 1994). Animal selectivity of regrowth can lead to overgrazing of some species or areas, permitting invasion by non-planted species, while other areas or species are underutilized (Barker et al., 2002; Beuselinck et al., 1994). Additionally, grazing animals can leave shorter stubble if forced to maximize forage utilization (Beuselinck et al., 1994), exposing susceptible plant parts to excessive heat or light (Harris et al., 1999). Finally, nutrient recycling under grazing can possibly lead to increased soil levels and subsequent leaching of some nutrients (Beuselinck et al., 1994; Sanderson et al., 2004). Data under grazing management in the irrigated steppe of the southern Rocky Mountains has not been reported for those binary mixtures tested by Guldan et al. (2000) and Lauriault et al. (2003).

The objective of this research was to compare DM yields and changes in species composition of the harvested forage of alfalfa, birdsfoot trefoil, cicer milkvetch, and kura clover in binary mixtures with tall rescue under different grazing frequencies in the irrigated steppe of the southern Rocky Mountains, USA.

MATERIALS AND METHODS

This research was conducted at New Mexico State University's Alcalde Sustainable Agriculture Science Center (36.09[degrees]N, 106.06[degrees]W, elev. 1745 m). The strip plot treatment was grazing frequency in which low frequency plots were grazed bimonthly (mid-May, mid-July, and mid-September) and the high frequency treatment was grazed monthly from mid-May to mid-September. Subplot pasture treatments consisted of established monoculture 'Alta' tall rescue (MONO), and tall rescue in a mixture with each of 'Alfagraze' or 'Wilson' alfalfa sown in separate plots (ALF/TF), 'Norcen' birdsfoot trefoil (BFT/TF), 'Monarch' cicer milkvetch (CM/TF), and 'NF90' kura clover (KC/TF). Cultivar within ALF/TF constituted the sub-subplot and year (1998-2001), as a component over time, was the sub-sub-subplot (Lauriault et al., 2003). There were three randomized complete blocks.

Test area characteristics, establishment, and management have been previously described (Guldan et al., 2000; Lauriault et al., 2003). The soil series was Fruitland sandy loam [coarse-loamy, mixed (calcareous), mesic Typic Torriorthent]. The field had been conventionally tilled and then prepared for furrow irrigation by forming 0.76-m wide beds on 0.91-m centers. On 23 Aug. 1993, plots 1.8 by 6.1 m were hand sown in four rows 15 cm apart on bed tops only. Mixtures were sown with the tall fescue and legume in alternating rows to minimize competition between grass and legume components during the seedling stage (Guldan et al., 2000; Sleugh et al., 2000).

Initial soil test results (1993) from the surface 15 cm indicated low levels of NaHC[O.sub.3]--extracted P (28.5 kg [ha.sup.-1]), moderate levels of K (1:5 [H.sub.2]O extract) (63 kg [ha.sup.-1]), and a pH of 7.4. Annually during the study period (1998-2001), the site received 49 kg P [ha.sup.-1] as granular 0-46-0. Additionally, every year MONO received 134 kg N [ha.sup.-1] [yr.sup.-1] as urea (46-0-0) dissolved in water and applied in equal split applications in mid-April, mid-June, and mid-August. No herbicides were used during the trial because the study area remained uniformly weed-free.

From 1994 to 1997, the test area was managed under a three-cut hay system (Guldan et al., 2000). Forage had been removed in mid-May, mid-July, and mid-September each year. Plots were irrigated approximately nine times during the growing season (April to November) each year since establishment and during the study period (1998-2001) to supplement precipitation and prevent moisture stress. Frequency and timing of irrigation was dependent on frequency, timing, and amount of precipitation. Estimates from a previous study indicated that irrigation amounts were approximately 13 cm per application (Guldan et al., 2000). 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.

Grazing was conducted in 1998, 1999, and 2000, with yearling beef cattle (Bos taurus L.) (initial liveweight approximately 200 kg) provided by a local producer that were housed at the center from before grazing in mid-May until after grazing in mid-September. Bloat preventive and water were provided at all times. When not grazing the test sites, animals grazed non-experimental mixed species pastures supplemented with hay, as needed. Grazing frequency treatments were fenced separately and grazed sequentially during each period for 3 to 4 d to remove all available forage above 5 cm and to prevent selective grazing (Leep et al., 2002; Edwards et al., 1996). The high frequency treatment had a shorter grazing duration after the first session each year. At least annually, and on the same date, all plots were chain harrowed to break up dung pats. There was no measurable regrowth after the September grazing period in any year.

Forage DM yields were measured in mid-May 1998 to 2000, immediately before grazing, and again in mid-May 2001, when the test was concluded. Data for 1998, taken before the initiation of grazing treatments, was used to establish a baseline to determine treatment effects after they were imposed. For each harvest, a 0.836-[m.sup.2] quadrat was hand-clipped from each plot leaving approximately 5-cm stubble. Placement of the quadrats was such that a representative cross-section of the furrow-bed continuum was obtained in each sample. The area of the sample thus included two seeded rows of the legume and two of the tall rescue from the mixtures or four rows of tall fescue from MONO. 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, species were clipped and bagged separately. All samples were dried for 48 h at 65[degrees]C to determine DM yield of each component species within the sample. Combined DM yield of each sample was calculated as the sum of the components and percentage of grass in the sward was calculated by dividing the grass DM yield by the combined DM yield.

Weather data were collected from a National Weather Service station located within 1 km of the study area. Mean monthly temperatures across years (1998-2001) were within the range of adaptation for the species tested, but warmer than the long-term average (Table 1). In general, the average annual precipitation during the study period was above the long-term average, but there were considerable differences between years in precipitation amount and distribution (Table 1).

The test was analyzed as a strip-split-split plot over time (Littell et al., 1996) with grazing frequency, pasture, cultivar within pasture, and year as the strip, sub, sub-sub, and sub-sub-subplots, respectively. Data for percentage of grass in the sward, DM yield of component species (grass and legume DM yield), and combined DM yield were subjected to SAS PROC MIXED (SAS Inst. Inc., 2000) analysis of variance to test the main effects of grazing frequency, pasture, cultivar within pasture, and year and all possible interactions. The Proc MIXED procedure allocated all degrees of freedom and associated variance for cultivar within pasture within alfalfa.

Rep x grazing frequency, rep x grazing frequency x pasture, rep x grazing frequency x cultivar within pasture, and residual mean squares were considered random and used as denominators for tests of significance (Littell et al., 1996). When an interaction was indicated, sequential analysis was conducted by pasture and then by year within pasture until no interaction remained. Additionally, linear, quadratic, and cubic effects of year as a time component were generated as continuous variables in the dataset and used to determine the nature of differences between grazing system treatments or pasture treatments across years. Protected least significant differences were used to determine where differences occurred between grazing frequencies within pastures and years. All differences reported are significant at P [less than or equal to] 0.05.

RESULTS AND DISCUSSION

As in other studies using these pasture treatments (Guldan et al., 2000; Lauriault et al., 2003), differences between cultivars within ALF/TF were few and will not be reported. Leep et al. (2002) and Hermann et al. (2002) also reported that differences among cultivars were not biologically significant and published only species means.

Grass DM yields were higher than those previously measured under three-cut hay management (1.48 Mg [ha.sup.-1], Lauriault et al., 2003). No differences occurred in grass DM yield for any main effect, except year (1.36, 1.90, 2.36, and 2.22 Mg [ha.sup.-1] for 1998 to 2001, respectively, LSD = 0.33). And there were no interactions. Harmoney et al. (2001) measured a decrease in grass and total DM mass of continuous and rotational (using a grazing frequency similar to the low frequency grazing treatment reported here) stocked mixed pastures compared with ungrazed plots. The 20-yr-old grass pasture used in that study had been recently renovated with a diverse mixture of forage legumes (Harmoney et al., 2001).

Average values for legume DM yield for BFT/TF and KC/TF (Fig. 1) were lower than May legume DM yields for the same species and mixtures when cut 3 times for hay (0.6 and 3.4 Mg [ha.sup.-1] for BFT/TF and KC/TF, respectively, Lauriault et al., 2003). This is consistent with the results of Edwards et al. (1996), who reported that white clover (Trifolium repens L.) patch size increased and harvested mass was greater in cut perennial ryegrass (Lolium perenne L.)-white clover swards, while patch size remained unchanged in grazed swards.

[FIGURE 1 OMITTED]

The year x grazing frequency x pasture treatment interaction existed because a difference in legume DM yield occurred between the grazing treatments within ALF/TF that did not occur in any other pasture treatment (Fig. 1). The interaction was no longer significant when data for 1998 were removed, indicating that it was strictly due to initiation of the grazing frequency treatment. Once the difference between grazing frequency treatments within ALF/TF was established, ALF/TF pastures responded similarly to environmental influences of climate and management in spite of grazing frequency, as did the other pasture treatments in which there was no difference between grazing frequency treatments (Fig. 1).

[FIGURE 1 OMITTED]

Hermann et al. (2002) also reported a decline in yield of the alfalfa component after the first year of grazing, attributing the decline to heavy spring precipitation and trampling by cattle. Precipitation at Alcalde in 1998 was above average (Table 1), but the excess all occurred after cattle were removed. The increased frequency of trampling in the high frequency grazing treatment could, however, have had an effect (Beuselinck et al., 1994). Lauriault et al. (2004) also observed a yield difference between grazed and ungrazed alfalfa varieties after the first winter-long grazing period. This difference, which was attributed strictly to the initiation of grazing, remained consistent the next year (Lauriault et al., 2004). Additionally, Tracy and Sanderson (2004b) measured a mixture yield decline when mowing frequency changed from a 4-wk interval to a 2-wk interval. These researchers also noted that once the initial difference occurred, it remained consistent in subsequent years with no further interaction between treatment and time because of environmental effects.

Harmoney et al. (2001) measured an increase in both legume DM mass and percentage during 3 yr after renovating a 20-yr-old cool-season grass pasture. In that study, which included a seeded legume mixture of annuals, biennials, and perennials, the rapidly establishing biennials and short-lived perennials [birdsfoot trefoil, red clover (T. pratense L.), and white clover] dominated the legume component of the pastures during the 3 yr after seeding (Harmoney et al., 2001). The white clover component increased under continuous stocking, while both red clover and birdsfoot trefoil declined (Harmoney et al., 2001). Under rotational stocking, white clover declined and the others remained constant (Harmoney et al., 2001). In ungrazed plots, white clover increased then decreased, red clover decreased, and birdsfoot trefoil increased (Harmoney et al., 2001). These differences over time were likely related to the effect of management on competition (Edwards et al., 1996; Harris et al., 1999), reseeding opportunities (Tracy and Sanderson, 2004b), and changes in soil nitrogen balance (Edwards et al., 1996; Harris et al., 1999; Sanderson et al., 2004).

Among long-lived perennial species in that study (Harmoney et al., 2001), contribution by alfalfa to the legume component was likely limited by the more rapidly establishing annuals and biennials. Still, alfalfa was the most consistent across management regimes. Cicer milkvetch did not contribute until the third year after seeding and then only at low levels and kura clover was not measurable at all during the 3-yr trial (Harmoney et al., 2001). This response during establishment by both cicer milkvetch and kura clover was consistent with but slower than the observations of Guldan et al. (2000) for new seedings. Lauriault et al. (2003) stated that after 4 yr under lax hay management, binary mixture proportions equilibrated and remained unchanged for another 4 yr.

Harmoney et al. (2001) attributed increasing legume proportion and DM mass over years to decreased competition by grass because of disturbance by grazing. In the research presented here, increased grazing disturbance of the high frequency grazing treatment decreased the alfalfa component compared with the low frequency grazing treatment. This decline may have been due to death of weaker plants and the inability of alfalfa to replenish stands by reseeding (Tracy and Sanderson, 2004b) or clonal growth (Harris et al., 1999). Edwards et al. (1996) found that once component proportions stabilized in white clover-perennial ryegrass pastures, white clover patches remained the same size but move slowly as some areas senesce and stolons infiltrate into other areas. This phenomenon may be associated with soil N status and may partially explain the changes over time in kura clover legume DM yield (Fig. 1).

Canopy architecture affects selective harvesting by both grazing animals and equipment (Edwards et al., 1996). According to Seman et al. (1999), the 0- to 10-cm layer of ungrazed tall rescue had the highest density of forage mass compared with other strata in the canopy. Both Dougherty et al. (1990) and Seman et al. (1999) found that the 10- to 20-cm stratum of an ungrazed alfalfa canopy was most dense. White clover leaves also occur mainly in the upper level of the canopy (Edwards et al., 1996), similarly to kura clover. Arias et al. (1990) found that animals grazing tall fescue would utilize forage above a 10-cm horizon, avoiding pseudostems in the horizon below. The most dense stratum of legume canopies are removed during grazing but not the most dense stratum of the companion grass. Edwards et al. (1996) stated that legumes, such as white clover, that tend to have less leaf material in the lower strata are put at a competitive disadvantage to grasses when their leaf material is removed. They attributed lack of increase in white clover patch size under grazing to this phenomenon. Alfalfa harvested as hay or rotationally stocked also has less leaf area in the lower canopy (Dougherty et al., 1990; Lauriault et al., 2005a; Seman et al., 1999). The more frequent defoliation of the high frequency treatments might have put the alfalfa at a competitive disadvantage to the tall rescue, leading to the significant year x grazing frequency x pasture treatment interaction for legume DM yield.

Average percentage grass in the sward for each pasture treatment (55, 92, 87, 49, and 100% for ALF/TF, BFT/TF, CM/TF, KC/TF, and MONO, respectively, LSD = 11) was similar to those measured by Lauriault et al. (2003) at this location Under a three-cut hay management regime. Leep et al. (2002) reported grass percentages of 33 to 95% over 2 yr in mob-grazed binary mixtures of birdsfoot trefoil and several perennial cool-season grasses, including tall rescue. The decline in legume DM yield of ALF/TF grazed monthly was likely the cause of a significant year x grazing frequency x pasture treatment interaction (data not shown). Lauriault et al. (2003) reported that component proportions were more highly correlated to the legume component than to the grass component.

Combined (grass DM yield + legume DM yield) DM yield across treatments (Fig. 2) was similar to May yields under three-cut hay management (2.6 Mg [ha.sup.-1], Lauriault et al., 2003). At >1.5 Mg [ha.sup.-1], production was sufficient to prevent weed encroachment (Clark, 2001; Tracy and Sanderson, 2004a), as also demonstrated by the lack of any need for chemical weed control.

[FIGURE 2 OMITTED]

The year x pasture treatment interaction for combined DM yield existed, in part, because MONO, ALF/TF, and CM/TF treatments all increased linearly across years in combined DM yield while BFT/TF and KC/TF did not (Fig. 2). The lack of this effect in BFT/TF and KC/TF (Fig. 2) demonstrated a more consistent level of productivity across years for those pasture treatments, which is desirable. The year x pasture treatment interaction also was due to the year-to-year fluctuation in ALF/TF and KC/TF indicated by a significant cubic effect for each of those pasture treatments (Fig. 2). Lauriault et al. (2003) reported a similar interannual trend across years for combined DM yield of kura clover mixed with tall rescue managed under a three-cut hay system at this location, stating that the pattern was driven mainly by legume DM yield.

Loiseau et al. (2001) found that yields of monoculture white clover and the white clover component of binary mixtures with perennial ryegrass oscillated over a 2-yr cycle related to N fluctuations in the soil. Depletion of mineral N by grass growth causes an increase in Rhizobium activity and legume growth (Beuselinck et al., 1994). The companion grass was more competitive than the legume for N, so soil N was again depleted and the cycle continued (Beuselinck et al., 1994; Loiseau et al., 2001). The significant cubic trend in combined DM yield was likely not exhibited by BFT/TF and CM/TF (Fig. 2) because of their low legume DM yield (Fig. 1). Chevrette et al. (1960), however, did indicate a biennial fluctuation over 5 yr in yield of binary mixtures of birdsfoot trefoil with several grasses, as well as binary mixtures including alfalfa.

The lack of any effect for grazing frequency or any interaction involving grazing frequency for combined DM yield, when there had been a year x grazing frequency x pasture interaction for legume DM yield (Fig. 1), suggested that mixture components were sufficiently complementary to overcome the effects of grazing frequency treatment every year and maintain a relatively stable level of production from year to year despite grazing treatments or environmental differences (Haynes, 1980; Sanderson and Elwinger, 2002). It also suggested that under both the grazing treatments imposed, KC/TF combined DM yield also was driven by the legume component, as was ALF/TF grazed every other month, similarly to the findings of Lauriault et al. (2003). Combined DM yield of ALF/TF grazed every month and BFT/TF and CM/TF in both grazing treatments, however, was driven more by the grass component as it benefited from nitrogen (Edwards et al., 1996; Loiseau et al., 2001) supplied by an albeit lesser yield contribution from the legumes.

Wedin et al. (1965) found that when the legume proportion of mixed swards [predominantly smooth bromegrass (Bromus inermis L.)-alfalfa] fell below 20%, total mixture yield was less than grass + 157 kg N [ha.sup.-1] [yr.sup.-1]. When 45 kg N [ha.sup.-1] [yr.sup.-1] was applied to legume depleted stands, animal performance was similar to grass + N with additional benefit gained by applying 157 kg N [ha.sup.-1] [yr.sup.-1] to similar stands in which the legume component was <20% (Wedin et al., 1965). The difference between the results reported here, in which no nitrogen was applied to pastures having <20% legume component and those of Wedin et al. (1965) might be related to the difference between established legumes in a stabilized community (Lauriault et al., 2003) and a new seeding, in which the legumes winterkilled before the community became stabilized (Wedin et al., 1965). Harris et al. (1999) stated that the legume proportion of New Zealand white clover-perennial ryegrass dairy pastures equilibrated at 15% and that it was difficult to develop and maintain higher proportions. It is likely that once the community becomes stabilized in a grazing system and nutrient recycling through manure is consistent (Sanderson et al., 2004), alfalfa, birdsfoot trefoil, and cicer milkvetch, also can supply the nitrogen requirement to grass at much lower proportion levels. In the case of ALF/TF grazed monthly, which was 80% grass, yield compensation by the grass component was sufficient to provide combined DM yield nearly equal to ALF/TF grazed every other month, which was still 60% alfalfa. This concept remains to be demonstrated for kura clover because total mixture yield (combined DM) was still being driven by the legume component for both grazing treatments.

Harmoney et al. (2001) stated that birdsfoot trefoil persisted well in unharvested systems. Their (Harmoney et al., 2001) research also showed that birdsfoot trefoil was not persistent when continuously grazed; however, component proportions were stable under infrequent rotational stocking, comprising approximately 25% of the harvested sward. Continuous stocking used by Harmoney et al. (2001) likely prevented reseeding (Tracy and Sanderson, 2004b) by the birdsfoot trefoil. Grazing management only slightly more lax than the low frequency grazing treatment of the study reported here, more similar to that of the rotational stocking treatment used by Harmoney et al. (2001), might also allow reseeding by birdsfoot trefoil and lead to higher legume proportions. Although combined DM yield by BFT/TF was much lower than average combined DM yields of both ALF/TF and KC/TF, Clark (2001) stated that animal performance on lower yielding birdsfoot trefoil could be higher than animal performance on alfalfa. Additionally, Harris et al. (1999) found that although deferred grazing of white clover-perennial ryegrass pastures might reduce forage nutritive value because of increased maturity, animal performance was not compromised, likely because of higher legume content of white clover-perennial ryegrass pastures. Deferred grazing of ALF/TF in the low frequency grazing treatment also should lead to higher animal performance because of the higher legume DM yield.

CONCLUSIONS

Birdsfoot trefoil and cicer milkvetch legume contribution to combined DM yield were low, but binary mixtures of those species with tall rescue yielded as well as monoculture tall rescue + 134 kg N [ha.sup.-1]. Both alfalfa- and kura clover-tall rescue produced greater yields than monoculture tall fescue + 134 kg N [ha.sup.-1]. Component proportions in grazed binary grass-legume mixtures in the irrigated steppe of the southern Rocky Mountains fluctuate much the same as they do under hay management in the region. Alfalfa and kura clover DM yield followed a biennial oscillation in combined DM yield similar to white clover while birdsfoot trefoil and cicer milkvetch did not, possibly because they yielded much less than the other legumes. Legume DM yields of Birdsfoot trefoil-, cicer milkvetch-, and kura clover-tall fescue were unaffected by grazing frequency. The legume component of alfalfa-tall fescue was maintained across years when defoliated every 2 mo, but it was reduced by monthly defoliation. Changes in component proportion because of defoliation frequency had no measurable effect on combined DM yield of established binary mixtures of tall fescue with alfalfa. Birdsfoot trefoil-tall fescue and kura clover-tall rescue provided more uniform yield distribution across years than binary mixtures of tall rescue with alfalfa or cicer milkvetch and offer alternatives to monoculture tall rescue + 134 kg N [ha.sup.-1] [yr.sup.-1] and alfalfa-tall fescue as long-term pastures in the irrigated steppe of the southern Rocky Mountains.

ACKNOWLEDGMENTS

The New Mexico State University Institutional Animal Care and Use Committee approved the use of animals in this project. We gratefully acknowledge the technical assistance of David J. Archuleta, Val S. Archuleta, and Greg Sopyn; office assistance from Phyllis Moya, Dora Valdez, Augusta Archuleta, and Patricia Lopez; the folks at the NMSU Library Document Delivery Service; and Dennis Braden, manager of El Sueno del Corazon Ranch, and his staff for providing the grazers.

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Leonard M. Lauriault, * Steven J. Guldan, Charles A. Martin, and Dawn M. VanLeeuwen

L.M. Lauriault, Tucumcari Agric. Sci. Ctr., New Mexico State Univ., 6502 Quay Road AM.5, Tucumcari, NM 88401; S.J. Guldan and C.A. Martin, Alcalde Sustainable Agric. Sci. Ctr., New Mexico State Univ.. RO. Box 159, Alcalde, NM 87511; D.M. VanLeeuwen, Dep. of Agricultural and Extension Education, Agricultural Biometrics Service, New Mexico State Univ., P.O. Box 30003 MSC 3501, Las Cruces. NM 88003-8003. A contribution of the New Mexico Agric. Exp. Stn., New Mexico State Univ., Las Cruces. Received 7 Feb. 2005. * Corresponding author (lmlaur@nmsu.edu).

Abbreviations: ALF/TF, mean of alfalfa cultivars mixed with tall rescue: BFT/TF, birdsfoot trefoil mixed with tall rescue: CM/TF, cicer milkvetch mixed with tall fescue; DM, dry matter: KC/TF, kura clover mixed with tall fescue: MONO, tall fescue monoculture.
Table 1. Monthly mean temperatures and total precipitation for
1998-2001 and the long-term averages (1953-2001) at Alcalde, NM.

                          Mean temperature

                             [degrees]C

Month        1998    1999    2000    2001    Long term

January       0.0     2.3     0.4    -1.6      -1.0
February      1.3     3.9     5.2     2.0       2.2
March         5.1     7.6     6.9     5.7       5.7
April         8.7     9.1    12.7    10.6      10.1
May          15.0    13.3    17.1    15.8      14.7
June         18.7    18.6    21.3    20.3      19.6
July         22.8    22.3    23.5    22.5      22.3
August       21.8    20.2    23.0    20.8      21.2
September    19.4    16.4    18.5    17.6      17.1
October      11.0    11.8    11.2    10.6      11.1
November      5.7     6.2     1.1     5.6       4.4
December      1.9    -1.3     0.3    -1.2      -0.4

Annual       11.8    12.0    11.8    10.7      10.5

                            Total precipitation

                                     mm

Month         1998      1999      2000      2001     Long term

January        2.03      8.38      4.57     27.18      9.40
February      10.92      1.02      0.00      7.37      8.64
March         22.10     25.15     20.07     11.18      12.19
April          6.10     36.07     16.26     14.48      13.72
May            0.00     22.10      0.00     26.42      19.30
June           6.86     31.24      6.60      1.02      20.57
July          56.64     69.34     51.56     61.72      35.81
August        57.91     89.15     52.07     46.23      48.77
September     16.00     23.88     10.41      2.54      29.97
October      104.90      8.64     55.88      6.10      25.91
November      19.30      0.00     27.69      8.89      17.27
December       0.00      4.06      9.14      0.76      9.65

Annual       302.77    319.02    254.25    213.87     247.90
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Author:Lauriault, Leonard M.; Guldan, Steven J.; Martin, Charles A.; VanLeeuwen, Dawn M.
Publication:Crop Science
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Date:Jan 1, 2006
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