Published in Agron. J. 96:352-358 (2004).
© American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA
PRODUCTION PAPER
Yield and Nutritive Value of Irrigated Winter Cereal Forage Grass–Legume Intercrops in the Southern High Plains, USA
L. M. Lauriault* and
R. E. Kirksey
Agric. Sci. Center at Tucumcari, New Mexico State Univ., 6502 Quay Road AM.5, Tucumcari, NM 88401
* Corresponding author (lmlaur{at}nmsu.edu).
Received for publication June 26, 2003.
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ABSTRACT
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With dwindling water supplies, alfalfa (Medicago sativa L.) and corn (Zea mays L.) producers in the Southern High Plains (USA) seek alternative forages for the dairy industry. At New Mexico State University's Agricultural Science Center at Tucumcari, cereal forage monocultures and intercrops with legumes were subjected to two irrigation treatments during two growing seasons in a Canez fine sandy loam (fine-loamy, mixed, thermic Ustollic Haplargid). Dry matter (DM) yield of monocultures averaged 3.76, 3.90, 5.55, 5.59, and 3.17 Mg ha–1 for rye (Secale cereale L.), barley (Hordeum vulgare L.), wheat (Triticum aestivum L.), triticale (x Triticosecale rimpaui Wittm.), and oat (Avena sativa L.), respectively. Cereal forages irrigated once in a growing season yielded equally to those watered twice with average precipitation (2000–2001, 408 mm), but not in a dry growing season (2001–2002, 245 mm) (6.15, 5.41, 1.90, and 3.21 Mg ha–1 for cereal forages irrigated once or twice in 2000–2001 or 2001–2002, respectively). Also, levels of forage nutritive components were greatest when irrigated once in 2001–2002. Intercropping with winter pea [Pisum sativum subsp. arvense (L.) Poir] or hairy vetch (Vicia villosa Roth.) reduced yield of wheat and triticale compared with monocultures, but these yields were still greater than those of the other cereal forages and winter pea improved quality indicators when intercropped with wheat or triticale. Water can be conserved in the Southern High Plains by irrigating cereals only as needed for germination or to promote fall growth.
Abbreviations: CP, crude protein • DAP, days after planting • DM, dry matter • LSD, least significant difference • NDF, neutral detergent fiber • NEL, net energy for lactation • NFTA, National Forage Testing Association • NIRS, near infrared reflectance spectroscopy • NS, not significant
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INTRODUCTION
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FORAGE CROPS constitute the major component of dairy feeds (Mustafa et al., 2000). A growing dairy industry in the Southern High Plains and the Pecos and Rio Grande River valleys of the USA has led to increased demand for alfalfa and corn for hay, silage, or greenchop (New Mexico National Agric. Statistics Service, 2002a, 2002b). However, prolonged droughts, declining aquifers, and urban growth, coupled with interstate water compacts and judicial rulings in favor of endangered species, are limiting water available for irrigation (Turney, 2003). These factors create a need in the region for alternative species that are capable of producing dairy quality forage with less water. Hall and Kephart (1991) found that when environmental conditions limit production of perennial forage crops, annual species can be effectively used.
Warm-season and cool-season annual grasses are also used as hay, silage, and greenchop in dairy rations (Chapko et al., 1991; Mustafa et al., 2000) and are well adapted to the Southern Plains and the Southern High Plains of the USA (Malm et al., 1973; Rao et al., 2000). These forages, however, do not provide quality equal to that of alfalfa and must be supplemented with protein (Anil et al., 1998; Chapko et al., 1991). Hall and Kephart (1991) said that yield and quality of triticale were maximized slightly before heading in Idaho. Collins et al. (1990), in Wisconsin, recommended harvesting oat at boot to early head stage for livestock that required higher quality because oat quality would decline after heading.
Quality indicators of cereal forages tend to increase from the milk to dough stage due to dilution of indigestible fiber by the grain (Edmisten et al., 1998b). An increase in digestible energy is also beneficial to fermentation and provides more energy for livestock. Thus, cereal forages are often harvested at the soft dough stage when they are to be ensiled (Carr et al., 1998; Jedel and Helm, 1993; Mustafa et al., 2000). But Edmisten et al. (1998b) and Rao et al. (2000) both demonstrated a decrease in digestibility of cereal forages after heading, while Edmisten et al. (1998b) also measured the decline in nutritive value of cereal forages that were ensiled at progressively later stages of maturity.
Conversely, monoculture forage legumes tend to be deficient in energy and must be accompanied by a supplement (Anil et al., 1998; Mustafa et al., 2000). Mustafa et al. (2000) found that monoculture field pea silage was higher in starch but lower in crude protein (CP) than alfalfa silage, and pea silage was lower in neutral detergent fiber (NDF) but higher in CP than barley silage. They concluded that pea silage could replace alfalfa or barley silage in dairy diets with no change in intake, milk or lactose yield, or lactose percent (Mustafa et al., 2000). However, poor sward structure for harvesting and field curing is a disadvantage with monoculture pea, as well as many other annual forage legumes (Jedel and Helm, 1993).
Because quality of cereal forage is usually lower than alfalfa, cereal forages (barley and oat) are often mixed with field pea in the northern USA and Canada to increase protein content with no negative effect on total yield (Anil et al., 1998; Chapko et al., 1991; Hall and Kephart, 1991). Other legumes occasionally intercropped with cereal forages include vetches (Vicia spp.) (Anil et al., 1998). Anil et al. (1998) reviewed literature from the Mediterranean and coastal regions of western Europe that demonstrated a yield reduction when common vetch (V. sativa L.) was intercropped with oat, while in another study, oat–hairy vetch intercrops yielded 12 Mg ha–1 when oat comprised a high proportion of the seeding rate (Anil et al., 1998). The cereal provides support for the legume to aid in harvesting and drying in the windrow (Jedel and Helm, 1993). Other benefits of these mixtures include greater use of light, greater uptake of water and nutrients, enhanced weed suppression, and increased soil conservation (Anil et al., 1998). Cereal forages produce best with high moisture (Edmisten et al., 1998a), but they also perform well in semiarid regions (Malm et al., 1973). Winter pea and hairy vetch are also well adapted to the semiarid climates of the Southern High Plains, but they have not been widely used.
The objectives of this research were to compare compatibility of winter pea and hairy vetch with barley, oat, rye, triticale, and wheat and to measure selected nutritive components of cereal monocultures and cereal–legume intercrops as dairy feed in limited irrigation situations when harvested at the late-boot to early head stage in the Southern High Plains.
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MATERIALS AND METHODS
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The study was conducted at the New Mexico State University Agricultural Science Center at Tucumcari, NM, USA (35°12'0.5'' N, 103°41'12.0'' W; elev. 1247 m) in a field that had been in perennial cool-season grass production for 5 yr. The soil was Canez fine sandy loam with soil test levels of 67 mg kg–1 P (NaHCO3 extractant), 194 mg kg–1 K (ammonium acetate extractant), and a pH of 7.6. This soil had a rooting depth of approximately 1.5 m and a water holding capacity of 25 to 30 cm (Ross and Pease, 1974). Tests sown 1 Sept. 2000 and 30 Aug. 2001, were split-split-split plots in three randomized complete blocks where year (2000–2001 or 2001–2002) was the whole plot, irrigation regime (pre-irrigated only or pre-irrigated + irrigated in mid-October) was the subplot, winter cereal forage (barley, oat, rye, triticale, or beardless wheat) was the sub-subplot, and intercropped legume (none, hairy vetch, or winter pea) was the sub-sub-subplot.
Treatments, consisting of monoculture cereals and cereal–legume intercrops, were sown into a conventionally tilled seedbed formed into beds on 0.9-m centers for furrow irrigation using a disk drill with a 20-cm drill spacing that was fitted with a seed-metering cone. Individual plot size was 4.8 by 1.8 m. A 1.5-m skip was left between plots to establish uniform end-border effects. Seeding rates for monoculture small grains were 54, 36, 63, 56, and 67 kg ha–1 for barley, oat, rye, triticale, and wheat, respectively, or 87 L ha–1 for each species. For intercrops, the cereal seeding rate was half that of the monoculture plus either 17 kg ha–1 hairy vetch or 56 kg ha–1 winter pea. Seed of intercrop components was combined in the same packet and thoroughly mixed before sowing. The legumes were not inoculated because of concern that nonuniform nodulation would interfere with the objectives of the studies. Rather, N (56 kg ha–1 as 46–0–0) was broadcast and incorporated preplant (22 Aug. 2000 and 20 Aug. 2001).
Irrigations were delivered through gated pipe and were of sufficient duration to completely wet the center of the beds for their full length. Historical irrigation flow rate data collected as described by Ziska et al. (1985) at this location was used to estimate that approximately 20 cm of water was applied with each irrigation.
Legume maturity and proportion in the harvested sward were visually rated immediately before harvesting. Top growth above 7.5 cm of monoculture cereal forages and cereal–legume intercrops were harvested when the associated cereal was in the late-boot to early head stage using a self-propelled forage plot harvester equipped with a reciprocating blade and electronic scales. Harvest width was 1.3 m, leaving 0.3 m to reduce any border effect from adjacent plots. Immediately after weighing fresh forage in the field, a sample of approximately 400 g was collected and placed in a paper bag and sealed inside a plastic bag to conserve moisture until harvesting was complete, at which time the samples were weighed and plastic bags removed before drying for 48 h at 70°C. Samples were then reweighed to determine DM concentration, which was used to convert fresh harvest weights to DM yield. Dried samples were ground to pass through a 1-mm screen and shipped to a National Forage Testing Association (NFTA) (Omaha, NE; www.foragetesting.org; accessed Sept. 2003; verified 4 Dec. 2003) certified laboratory that is also a member of the NIR Consortium (www.uwex.edu/ces/forage/NIRS/home-page.htm; accessed Sept. 2003; verified 4 Dec. 2003) (Ward Labs, Kearney, NE) for near infrared reflectance spectroscopic (NIRS) analyses for CP, NDF, and net energy for lactation (NEL) using a general equation that had been enhanced by including data from cereal forages (Dan Undersander, personal communication, 2003). Brown et al. (1990) found that the broad-based equations returned nutritive values with a degree of accuracy similar to those developed using subsets for species-specific groups.
Weather data were collected from a National Weather Service cooperative station located at the Agricultural Science Center within 1 km of the study area (Table 1). The climate in the region is continental, characterized by cool, dry winters and warm, moist summers. Approximately 83% of the precipitation occurs as intermittent, relatively intense rainfall events from April through October. July and August typically have the highest precipitation (Table 1). The 2000–2001 growing season was slightly warmer than average and precipitation was average, but abnormally well distributed for winter cereal forage production. However, the 2001–2002 season was much warmer and drier than average.
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Table 1. Monthly mean air temperatures and total precipitation at Tucumcari, NM, during the 2000–2001 and 2002–2002 growing seasons and the long-term (1905–2002) means.
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Yield and nutritive component data were subjected to analysis of variance and PROC GLM techniques (SAS Inst., 2000) for tests of main effects and interactions. All differences reported here are significant at P < 0.05. Cereal and legume treatment means were separated using Fisher's protected least significant difference (P < 0.05).
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RESULTS AND DISCUSSION
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Although the main effects of year, irrigation treatment, cereal, and legume, were all significant for every measured variable, interactions existed for each that will be discussed.
Harvest Date
Harvest dates for the cereal forages were similar to, or slightly later than, those used by Edmisten et al. (1998a) at a similar stage of maturity and latitude in North Carolina (222, 231, 238, 244, and 251 d after planting [DAP] for rye, barley, wheat, triticale, and oat, respectively). Rao et al. (2000) found that wheat matures 8.5 d earlier than triticale in the Southern Plains. Maloney et al. (1999) stated that rye matured at least 7 d earlier than wheat and triticale in Wisconsin.
Winter pea was vegetative through the barley harvest. It was at early bloom for wheat and triticale, and at full bloom for the oat harvest. Hairy vetch was in early bud when rye and barley were harvested, early bloom at wheat harvest, and full bloom for triticale and oat. Proportion of winter pea in harvested forage increased from the rye harvest through the oat harvest (Table 2). The proportion of hairy vetch intercropped with rye, barley, wheat, triticale, and oat did not increase as steadily over time leading to the year x irrigation interaction for legume proportion. Differences in the rate of increase occurred between growing seasons that might have been due to a reduced proportion of winter pea when intercropped with rye, triticale, and wheat in the dry growing season (Table 2).
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Table 2. The effect of legume intercropping on legume proportion of winter cereal forages at Tucumcari, NM, USA, in years of average (2000–2001, 408 mm) and low (2001–2002, 245 mm) precipitation.
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Hall and Kephart (1991) found that seedling populations in triticale–pea intercrops were well correlated with target ratios, indicating that any lack of emergence was consistent across component forage. In the present study, cereal forages established consistently uniform stands while establishment of winter pea was more uniform throughout individual plots than the hairy vetch. A higher seeding rate for either legume, even the hairy vetch would, however, not likely have increased legume contribution to the harvested sward for any cereal except possibly oat, because legume plant size appeared to be a factor in the level of contribution at each harvest date. Anil et al. (1998) stated that the benefits of cereal–legume intercrops were optimized as the species complimented each other. In the present study, neither legume complimented rye or barley and hairy vetch did not contribute greatly to any cereal forage because they matured too early for the legume to achieve a plant stature sufficient to make a contribution (Table 2).
Because of differences between growing seasons in precipitation in fall and spring (Table 1), competition by rye, triticale, and wheat could have occurred either during the seedling and fall growth period or in the spring when active growth resumed. The availability of irrigation water during the dry growing season (2001–2002) might actually have enhanced competition by the cereal forages causing a reduction in legume proportion (Table 2).
Forage Yield
Mean annual yields of the monocultures measured in this study in 2000–2001 (Table 3) were consistent with those for the same species measured by Edmisten et al. (1998a) in North Carolina, Chapko et al. (1991) in Wisconsin, and Malm et al. (1973) in southern New Mexico. There was a year x irrigation interaction for DM yield that is partially attributable to precipitation. In 2001–2002, the pre-irrigation only treatment yielded less than cereals that were also irrigated in mid-October (Table 3). This effect is likely related to the difference in precipitation between growing seasons (Table 1). All but 3 mm of the precipitation that fell in October 2000 fell after the second irrigation had been applied, diluting the effect of the October irrigation. Additionally, high precipitation in March 2001 continued to promote growth of the cereals. The lack of precipitation in fall 2001 and spring 2002 is evident in both treatments for 2001–2002, but more so for the pre-irrigated only treatment (Table 3). Hall and Kephart (1991) stated that interspecific relationships tend to be antagonistic in early growth stages. Lack of sufficient soil moisture might have enhanced interspecific competition in fall 2001. Chapko et al. (1991), Collins et al. (1990), and Rao et al. (2000), in central Oklahoma, found that forage yields of small grains were depressed by moisture stress. Rao et al. (2000) also reported that wheat and triticale matured earlier due to low precipitation. However, in the present study, maturity does not appear to have been affected by low moisture because harvest dates were only 1 d earlier for the species tested, except for barley, which was harvested 6 d earlier in 2002 than 2001.
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Table 3. The year x irrigation effect on legume proportion, forage dry matter yield, neutral detergent fiber (NDF), and net energy for lactation (NEL) of winter cereal forages at Tucumcari, NM, USA, in years of average (2000–2001, 408 mm) and low (2001–2002, 245 mm) precipitation.
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Moisture stress, however, does not entirely account for the difference in DM yield between growing seasons. In another study involving cereal forage under similar management at this location (Lauriault, unpublished data, 1999–2001), there was a decrease in productivity in the second growing season as well. In that study, the first growing season (1999–2000) had only 291 mm and produced 8.65 Mg ha–1, while in the second growing season (2000–2001) (408 mm precip.), yields were only 6.18 Mg ha–1. Field history for both tests was similar. The present study site had been in perennial cool-season grass production for 5 yr while the other study site had been in permanent warm- and cool-season grass pastures for 10 yr and, as previously mentioned, irrigation (pre-irrigated + mid-October) and fertility management were the same. The soils used for both experiments were also similar, having <10 g organic matter kg–1. Turning under actively growing cool-season grasses likely released N that was available for plant use in the first growing season, especially in sandy soils such as those used in both of these trials (Loiseau et al., 2001). In both studies, most of the plant material was removed from the plots at harvesting, but the remaining straw and regrowth from the first test year was turned under as part of land preparation for the second season. The added straw likely had a high C/N ratio, causing soil microbes to utilize the applied N before the cereals could (Brady, 1974; Mueller et al., 1998). Mueller et al. (1998) found that sandy loam soils amended with chopped barley straw had higher N disappearance rate than those amended with either chopped whole plant corn or bluegrass (Poa pratensis L.).
Lauriault et al. (2002) found a positive relationship between N applications and either precipitation or irrigation for tall wheatgrass (Agropyron elongatum [Host] Beauv.) and Collins et al. (1990) mentioned that rainfall could stimulate N uptake of oat, leading to increased growth rate. It is possible that there was a combined effect of precipitation and available-N that led to the difference between growing seasons such that either limited precipitation or limited available-N might have caused the effect in 2001–2002, even if the other factor had not been limiting (Table 3).
Irrigation water is not available from late October through mid- to late April at this location. By mid-April (227 DAP in the present study), most cereal species in this region have begun elongation of reproductive tillers and future forage production is limited. In areas where water is available year-round or as early as 1 March, producers have the opportunity to promote spring growth with irrigation, as did the precipitation in March 2001 (Tables 1 and 3). The availability of water for spring irrigation should also provide the opportunity for cereal forages to benefit from a spring fertilizer application (Collins et al., 1990; Edmisten et al., 1998a; Lauriault et al., 2002).
The year x cereal interaction for DM yield (Table 4) appears to be an interaction of magnitude. All species yielded less in 2002 than in 2001; however, the yield decrease of wheat and oat was numerically greater than for the others. Although rye was the most stable in yield from year to year (Table 4), it is also the earliest maturing and would be less likely to take advantage of earlier availability of irrigation water, warmer temperatures for growth, higher average precipitation that occurs in April compared with February and March (Table 1), or greater contribution to nutritive value from a legume component.
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Table 4. Forage dry matter yield and net energy for lactation (NEL) of winter cereal forages at Tucumcari, NM, USA, in years of average (2000–2001, 408 mm) and low (2001–2002, 245 mm) precipitation.
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The cereal x legume interaction for DM yield (Table 5) is likely due to a decrease in wheat and triticale yields when intercropped with either winter pea or hairy vetch. This contradicts the findings of Hall and Kephart (1991), who measured yield increases as the percent of winter pea sown with triticale increased. However, Carr et al. (1998), in North Dakota, found that yield of summer-grown barley–pea and oat–pea intercrops was equal to that of the monoculture at cereal seeding rates of 68 kg ha–1 and above. But when the seeding rate for cereals in intercrops was 34 kg ha–1, yields were less than the monoculture sown at 68 kg ha–1. In the present study, the seeding rate for the cereal in intercrops was half that of the monoculture, which was <68 kg ha–1 for all species, but no similar reduction in yield was measured for either oat or barley. Carr et al. (1998) did not include monoculture seeding rates <68 kg ha–1, but they did mention that seeding rate of the legume had no effect on stand establishment of the cereal, even when the seeding rate of the cereal was reduced. This indicates that any interspecific competition leading to a yield reduction at late-boot to early heading stage (Hall and Kephart, 1991) would occur after establishment rather than as a result of seedling death. Hall and Kephart (1991) reported interspecific competition in cereal–legume intercrops, even at less than optimum plant densities. The seeding rate for winter pea in the present study (56 kg ha–1) was very similar to the lower rate used by Carr et al. (1998) (57 kg ha–1).
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Table 5. The effect of legume intercrop on dry matter yield, crude protein, and net energy for lactation (NEL) of winter cereal forages at Tucumcari, NM, USA.
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Interestingly, the yield of oat was lower than barley, when both were grown as monocultures, but there was no difference between the yields of their intercrops with legumes (Table 5). The difference between monocultures of barley and oat is consistent with the results of Chapko et al. (1991). Although Jedel and Helm (1993) also found a lack of difference between barley–pea and oat–pea intercrops (in Alberta, Canada), this does not concur with Chapko et al. (1991) and neither does the lack of difference between monoculture barley and the barley–pea intercrop. Their (Chapko et al., 1991) results did show a difference in yield between oat–pea and monoculture oat that was numerically less than the difference measured in the present study (0.38 Mg ha–1, calculated from Table 5).
Yields of rye, barley, and oat as monocultures and intercrops were similar (Table 5). Even with the decline in yield when mixed with legumes, DM yields of wheat and triticale were still greater than other monocultures or cereal–legume intercrops, which was contrary to the findings of Jedel and Helm (1993), who compared barley–pea, oat–pea, and triticale–pea intercrops. Rao et al. (2000) also found no difference in monoculture wheat and triticale yield in the Southern Plains. Malm et al. (1973), in southeastern New Mexico, reported that among monoculture cereals barley had greater DM yields than triticale and oat, which were greater than wheat; rye had the lowest yield (15, 13, 13, 11, and 9 Mg ha–1 for barley, triticale, oat, and wheat, respectively) when irrigated with 910 mm of water in addition to 100 mm precipitation.
Forage Nutritive Value
Concentration of CP in cereal forage monocultures measured in the present study (Table 5) were similar to those measured by Edmisten et al. (1998b) for the same species sown in the fall and harvested at boot to heading stage. They are also similar to those measured by Chapko et al. (1991), but higher than those measured by Carr et al. (1998), both of which tested spring-sown monocultures and intercrops of barley and oat with pea. There was a year x irrigation x cereal interaction for CP concentration (Table 6) in which oat forage was lowest in 2000–2001 and highest in 2001–2002; this caused an interaction of rank, while differences between growing seasons for the other species were in magnitude. Additionally, October irrigation decreased CP concentration of wheat in the dry growing season (2001–2002) while the other cereal forages were unaffected (Table 6). Edmisten et al. (1998b) found that when rye, barley, wheat, and oat were harvested at boot stage, rye and barley had greater CP under rainfed conditions in North Carolina. The addition of hairy vetch had no effect on CP of any cereal forage except oat, whereas including winter pea increased CP concentration of the grass–legume mixture when intercropped with wheat, triticale, and oat forages, leading to a cereal x legume interaction (Table 5).
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Table 6. The effect of growing season and irrigation regime on crude protein concentration of winter cereal forages grown as monocultures and intercropped with selected legumes at Tucumcari, NM, USA, in years of average (2000–2001, 408 mm) and low (2001–2002, 245 mm) precipitation.
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Neutral detergent fiber (Table 3) was higher than what Edmisten et al. (1998b) measured, but less than that measured by Collins et al. (1990) for spring sown monoculture oat. One difference between what Collins et al. (1990) found and those of the present study may be stage of maturity at harvest. Collins et al. (1990) harvested oat cultivars at 50% heading (50% of all panicles had completely emerged); however, in the present study plots where harvested at late-boot to early head (50% of all panicles emerging). Collins et al. (1990) mentioned that higher NDF at heading was associated with dry conditions just before heading. In the present study, lowest NDF was measured in 2001–2002 for cereal forages that were pre-irrigated only, leading to a year x irrigation interaction (Table 3). There also was a year x cereal x legume interaction for NDF (Table 7) such that, in 2000–2001, NDF was decreased only when winter pea was intercropped with wheat or triticale; in 2001–2002, intercropping with winter pea decreased NDF in all cereal forage–legume intercrops compared with their monocultures, except rye, and hairy vetch caused a decrease in NDF when intercropped with triticale (Table 7). The findings for barley, wheat, triticale, and oat as monocultures or when intercropped with winter pea in the present study agree with those of Chapko et al. (1991), who stated that crude protein concentration and forage intake potential, the latter being largely determined by NDF, were increased by intercropping pea with barley or oat and that oat–pea forage was higher in quality than barley–pea forage.
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Table 7. The effect of legume intercropping on neutral detergent fiber (NDF) of winter cereal forages at Tucumcari, NM, USA, in years of average (2000–2001, 408 mm) and low (2001–2002, 245 mm) precipitation.
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Similarly to the decrease in NDF leading to the year x irrigation interaction, there was an increase in NEL across growing seasons for the pre-irrigated–only treatment (Table 3). For all species NEL was greater in the dry growing season (2001–2002) than in the average precipitation growing season (2000–2001) (Table 4), but there was also a year x cereal interaction in which the increase in NEL in the dry growing season (2001–2002) for wheat and rye was twice that of the other cereal forages. Finally, there was a cereal x legume interaction, such that intercropping legumes with rye and barley had no effect on NEL of the mixed forage compared with the monocultures (Table 5); wheat–pea, triticale–pea, and oat–pea forages had greater NEL than their respective cereal forage monocultures. Chapko et al. (1991) found that relative performance of cereal and pea forages was the same in drought years as in years of average precipitation, but yield would be lower and quality indices greater, as was the case in the present study.
Mustafa et al. (2000) compared quality of ensiled monocultures of alfalfa, field pea, and barley and measured 17, 19, and 10 g kg–1 CP; 37, 34, and 41 g kg–1 NDF; and 1.50, 1.52, and 1.49 mcal kg–1 NEL, concluding that, with the exception of low CP of barley, silages made with the three species were interchangeable for dairy rations with no effect on milk yield. Edmisten et al. (1998b) noted that there was little difference in quality between ensiled and nonensiled cereal forages harvested at the late boot to early head stage of maturity and that quality declined with maturity. Levels of the nutritive components measured in the cereal forages in this test should be suitable for use in dairy feeds, whether stored as hay or silage.
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CONCLUSIONS
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Forage DM yield of cereals and cereal–legume intercrops was increased in a less-than-optimum precipitation growing season in the Southern High Plains of the USA with irrigation, but there was a negative effect on forage quality. In years of adequate, well-distributed precipitation, irrigation can be reduced without any negative effect on DM yield. Winter pea did not begin its period of rapid growth early enough to improve yield or nutritive value of rye–pea forage, but nutritive value of wheat–pea and triticale–pea forages was greater than the respective cereal monocultures. Yields of wheat and triticale were reduced when intercropped with legumes, but they were still greater than rye, barley, and oat as monocultures or mixed with hairy vetch or winter pea. Producers in more southern areas of the Southern High Plains (i.e., Lubbock, TX, or Artesia, NM) might achieve better forage yield and quality using barley–pea or oat–pea intercrops compared with monocultures than were measured in the present study.
Further research is needed to determine optimum seeding rates for the mixtures and the relative N needs of cereal–legume mixtures compared with monoculture cereal forages as well as the feasibility and benefit of legume inoculation and optimum irrigation timing. Testing combinations of cereal and legume maturity classes might broaden the choice of species. Additionally, the effect of replacing current feedstuffs with cereal forage–legume mixtures on economic returns from milk yields must be substantiated along with a comparison of costs and returns for alfalfa production and cereal forage–legume production.
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ACKNOWLEDGMENTS
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We gratefully acknowledge the technical and field assistance of George Arguello, Eutimio Garcia, Martin Mead, and Leslie Robbins, and secretarial assistance of Patricia Cooksey.
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NOTES
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A contribution of the New Mexico Agric. Exp. Stn., New Mexico State Univ., Las Cruces.
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REFERENCES
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INTRODUCTION
