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Published in Agron. J. 96:1013-1020 (2004).
© American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA

PRODUCTION PAPER

Forage Potential of Intercropping Berseem Clover with Barley, Oat, or Triticale

Shirley M. Rossa,*, Jane R. Kingb, John T. O'Donovanc and Dean Spanerb

a Dep. of Renewable Resour., 751 GSB, Univ. of Alberta, Edmonton, AB, Canada T6G 2H1
b Dep. of Agric., Food and Nutritional Sci., 4-10 Agriculture-Forestry Cent., Univ. of Alberta, Edmonton, AB, Canada T6G 2P5
c Northern Agric. Res. Cent., Agric. and Agri-Food Canada, Beaverlodge, AB, Canada T0H 0C0

* Corresponding author (shirley.ross{at}ualberta.ca).

Received for publication May 1, 2003.

   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 SUMMARY AND CONCLUSIONS
 REFERENCES
 
Intercropping berseem clover (Trifolium alexandrinum L.) with silage cereals may increase forage yield and quality. Berseem clover was intercropped with barley (Hordeum vulgare L.), oat (Avena sativa L.), or triticale (xTriticosecale rimpaui Wittm.) at 30, 60, 90, 120, and 240 cereal plants m–2 at Edmonton, Alberta, from 1998 to 2001. Cereals dominated Cut 1 (silage-stage) yield, and berseem clover dominated regrowth yield. As cereal density decreased from 240 to 60 plants m–2, Cut 1 yield decreased from 10.5 to 9.3 Mg ha–1 dry matter (DM), berseem clover percentage of Cut 1 increased from 5 to 14%, and berseem clover regrowth yield (Cut 2) increased from 1.8 to 3.0 Mg ha–1 DM. Total season intercrop yields with barley or oat at 60 plants m–2 were ≥yields with 240 plants m–2. Total season intercrop DM yields did not differ among the three cereal species in 3 of 4 yr. Triticale intercrops had advantages of greater Cut 1 yield and greater berseem clover percentage in Cut 1. Barley intercrops had advantages of greater Cut 2 yield and greater total season protein yield. Greater Cut 2 yield with barley intercrops was related to earlier silage-stage (Cut 1) harvest date. Intercropping berseem clover with reduced seeding rates of cereals improved Cut 1 forage quality. When berseem clover was 20% of Cut 1 yield, neutral detergent fiber was 25 to 45 g kg–1 less than with cereals alone. The crude protein of berseem clover regrowth averaged 210 g kg–1, providing high quality late-season forage.

Abbreviations: ADF, acid detergent fiber • CP, crude protein • DM, dry matter • NDF, neutral detergent fiber


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 SUMMARY AND CONCLUSIONS
 REFERENCES
 
INTERCROPPING of berseem clover with spring cereals grown for silage may improve forage quality and yield. Potential benefits of intercropping include increased yields, increased protein and forage quality, N contributions from legumes, greater yield stability, and reduced incidence of pests, weeds, and diseases (Anil et al., 1998). However, farmers are unlikely to adopt the increased cost and complexity of managing intercrops without demonstrated evidence of potential advantages over monocropping.

A substantial amount of barley and oat grown in western Canada is used as forage. Research in western Canada has tested silage cereals in mixtures with other annual seed crops (Walton, 1975; Berkenkamp and Meeres, 1987), with pulse crops (Jedel and Helm, 1993), with both annual ryegrass (Lolium multiflorum Lam.) and annual legumes (Thompson and Stout, 1997; Stout et al., 1997), and with other small-grain cereals (Juskiw et al., 2000a, 2000b). Although the growing season is short in central Alberta, the period of several weeks after silage harvest can be used for additional forage production, as demonstrated with mixtures of spring and winter cereals (Baron et al., 1992; Jedel and Salmon, 1995).

The addition of Persian clover (Trifolium resupinatum L.) to barley–ryegrass mixtures in British Columbia reduced fertilizer needs, improved midseason forage yield, and improved forage nutritive value (Thompson and Stout, 1997). The addition of pulse crops to cereals has increased DM yields (Izaurralde et al., 1993), increased protein production (Walton, 1975; Berkenkamp and Meeres, 1987), or improved forage quality (Carr et al., 1998). Increasing the use of annual legumes in cereal cropping systems can improve sustainability through biological N fixation, reduction of weed competition, and increased soil organic matter (Izaurralde et al., 1993).

Berseem clover has demonstrated intercropping potential in other environments, but its intercrop potential in the Parkland region of western Canada is unknown. Berseem clover is a high-yielding, nutritious, cool-season forage crop thought to have originated in the Middle East (Knight, 1985). In research conducted in north-central Alberta, berseem clover outperformed six other clovers in yield and ability to compete with weeds (Ross et al., 2001). Intercropping berseem clover with cereals has increased the yield and quality of cereal forage crops in India (Singh et al., 1989), increased total DM yields without reducing cereal grain yields in Mexico (Reynolds et al., 1994) and Iowa (Ghaffarzadeh, 1997; Holland and Brummer, 1999), and improved forage quality, reduced fertilizer needs, and increased subsequent crop yields in British Columbia (Stout et al., 1997) and Iowa (Ghaffarzadeh, 1997). Intercropped with Italian ryegrass (Lolium multiflorum Lam.) in Spain, berseem clover provided a N equivalence of 80 kg N ha–1 per year (Caballero et al., 1994). Berseem clover improved the forage quality and yields of barley–ryegrass–legume intercrops more than did annual Medicago and Lespedeza species (Stout et al., 1997). Berseem clover was better adapted than crimson clover (Trifolium incarnatum L.) or white clover (Trifolium repens L.) for intercropping with wheat (Triticum aestivum L.) or barley to improve the ground cover, N use efficiency, and productivity of low-input systems (Reynolds et al., 1994). Holland and Brummer (1999) concluded that ‘Bigbee’ berseem clover was the best-performing cultivar in oat–berseem clover intercrops.

Little information is available on the effect of cereal seeding rate on the performance of cereal–berseem clover intercrops. Legumes are often less competitive than cereal or grass species. Berseem clover constituted only 14% of the forage yield from a 50:50 seed intercrop of berseem clover with Italian ryegrass (Caballero et al., 1994). Berseem clover yields were reduced about 50% when grown with oat (Welty et al., 1991; Holland and Brummer, 1999). Reduced cereal seeding rates may be required to increase the legume component of cereal–legume intercrops. Caballero et al. (1995) recommended that oat seed should not exceed 20% of an oat–vetch (Vicia sativa L.) mixture if a substantial vetch component is desired for forage quality.

The choice of cereal species may affect the performance of cereal–berseem clover intercrops. Studies of cereal intercrops in Alberta have found that triticale and wheat were less competitive in mixtures than were oat and barley (Berkenkamp and Meeres, 1987); forage yield and quality of pulse–cereal intercrops differed with oat, barley, or triticale (Jedel and Helm, 1993); and barley was more competitive than oat in cereal–cereal intercrops (Juskiw et al., 2000b). Yields of wheat–pea (Pisum sativum L.) intercrops were greater than barley–pea intercrops in England (Tofinga et al., 1993).

The objectives of this study were to test (i) the effects of cereal species on cereal–berseem clover intercrops, (ii) the effects of cereal seeding rate on cereal–berseem clover intercrops, and (iii) the feasibility of intercropping berseem clover with cereals for forage in a short-season growing environment.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 SUMMARY AND CONCLUSIONS
 REFERENCES
 
Intercrops of berseem clover with oat, barley, or triticale were grown at Edmonton (53°25' N, 113°33' W), AB, Canada, on a Malmo silty clay loam [orthic Black Chernozem (Typic Cryoboroll)] from 1998 to 2001. Experiments followed tilled fallow, and fields were disked and harrowed before seeding. Soil pH at test sites ranged from 5.7 to 7.0, and soil nitrate levels ranged from 34 to 56 mg kg–1 at 0- to 30-cm depth. No fertilizer was added except for the application of triple superphosphate 0–45–0 at approximately 28 kg ha–1 of P2O5 in 2000.

Berseem clover was intercropped with spring cereal cultivars that are used for forage in Alberta: ‘AC Lacombe’, a midmaturing, six-rowed spring barley; ‘Waldern’ oat, a late-maturing, high-yielding silage/feed oat; and ‘Pronghorn’, an early maturing, spring triticale. In 1998, the experimental design was a split-plot randomized complete block with cereal species as the main plot and cereal density as the subplot. There were three replicates, and subplot size was 2 by 6 m. Cereal densities were 240 (full rate), 120, and 60 plants m–2. In 1999, 2000, and 2001, the cereal densities were 240, 90, 60, and 30 plants m–2, and berseem clover sole crop treatments were added. In 2000 and 2001, two berseem clover sole crop treatments were included, with the harvest of one treatment (BE 1) coinciding with barley intercrops and the other (BE 2) coinciding with harvest of oat and triticale intercrops. In 1999, only BE 2 sole crop berseem clover treatments were included. All treatments were randomized in randomized complete block designs, with four blocks and plot size of 1.8 by 6 m.

Seeding and harvest dates are in Table 1. Cereals were seeded at 2.5- to 4-cm depth with a small-plot double-disc press drill. Bigbee berseem clover was inoculated with the appropriate Rhizobium trifolii and seeded at 15 kg ha–1. In 1998, cereals were seeded with a six-row disc drill at 18-cm row spacing, and berseem clover was cross-seeded with the same seeder. In 1999, 2000, and 2001, cereals were seeded with a four-row disc seeder with 23-cm row spacing. In 1999, berseem clover was hand-seeded by broadcasting on the surface and incorporated by raking. The cereals emerged in advance of berseem clover in 1999, so the plots were irrigated 3 wk after seeding to promote berseem clover growth. To reduce the potential for late relative emergence of berseem clover in 2000 and 2001, berseem clover was cross-seeded at a 1.5- to 2-cm depth at 18-cm row spacing using a six-row disc drill. Spring conditions were very dry in 2001, so plots were irrigated before and after seeding. Plots were hand-weeded.


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  		Table 1. Harvest dates for Cut 1 and Cut 2, with number of days after planting{dagger} or days of regrowth in parentheses, for cereal–berseem clover intercrops and berseem clover sole crops (BE) at Edmonton, AB, for 1998 to 2001.

 
Cut 1 was taken at silage stage (milk to soft dough) of the cereals. Subsamples were cut by hand at 5 to 7.5 cm above soil level and separated into berseem clover and cereal biomass. In 1998 and 2001, subsampling was from two quadrats sized 0.5 m2 or 0.6 m2 in each plot. Quadrats had been marked after emergence, with target cereal plant densities achieved through placement or thinning. For each plot in 1999 and 2000, species composition was measured from one randomly chosen subsample sized 0.23 m2 or 0.27 m2, and yield was measured from a 2.25-m2 area. After sampling, the remainder of plot growth was cut with a sickle mower and raked to remove the cut biomass. Cut 2 measured the regrowth at the end of the growing season in late September or early October. Subsampling for Cut 2 was from the marked quadrats in 1998 and 2001 and one randomly chosen 0.5-m2 area from each plot in 2000. In 1999, regrowth was not measured because it was negligible. Samples were dried for 72 h at 52°C and weighed. Species composition and DM yields were determined for all treatments. A subset of samples, mainly from treatments with cereal densities of 60 plants m–2, was analyzed for forage quality. Nitrogen was determined by the Kjeldahl mixed Cu/Ti catalyst method and multiplied by 6.25 for crude protein (CP) (AOAC, 1990). Acid detergent fiber (ADF) was determined according to Goering and Van Soest (1970) and neutral detergent fiber (NDF) according to Undersander et al. (1993).

Data were analyzed using analysis-of-variance techniques to determine significant treatment effects (P ≤ 0.05) using Statistical Analysis System (SAS Inst., 2000). Results for percentage of berseem clover in Cut 1 were transformed to square root of x + 0.5 for analysis to reduce the coefficient of variation to less than 25. Cereal density effects were originally separated with orthogonal contrasts, using coefficients derived in the IML procedure of SAS. Cereal density contrasts beyond quadratic were pooled as deviations. Where significant year x treatment interactions occurred (P ≤ 0.05), data are presented by year.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
SUMMARY AND CONCLUSIONS
 REFERENCES
 
Above-average temperatures in 1998 caused earlier cereal maturity and earlier dates of Cut 1 silage-stage harvests than in other years (Table 1). Seasonal mean temperatures for May to September were 16.5°C in 1998 and were near the 30-yr average of 14.5°C in other years. In north-central Alberta, cereal silage is usually harvested in August, and barley normally reaches silage stage earlier than oat and triticale. In all years, barley reached silage stage 8 to 9 d earlier than oat. Oat and triticale intercrops were harvested on the same date, except in 1998.

The percentage of berseem clover in intercrops was affected by moisture availability and the timing of berseem clover emergence relative to the emergence of cereals. A higher berseem clover percentage in intercrops in 2000 was associated with higher rainfall than in other years and emergence of berseem clover before cereal emergence (Table 2). Rainfall for May to September was near the 30-yr average (326 mm) in 2000 (330 mm) but was less than normal in 1998 (280 mm), 1999 (259 mm), and 2001 (267 mm). In 1999, the percentage of berseem clover in intercrops was nearly negligible when the clover emerged after cereal establishment. Relative time of emergence has been identified as an important factor in crop–weed competition (O'Donovan et al., 1985) and in legume–cereal competition in intercrops (Tofinga et al., 1993).


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  		Table 2. Mean Cut 1 dry matter (DM) biomass and Cut 1 percentage berseem clover by dry weight for cereal–berseem clover intercrops and berseem clover sole crops (BE) at Edmonton, AB, from 1998 to 2001.

 
Cereal Density Effects on Intercrops
Cut 1 DM yields were lowest for intercrops with cereal densities of 30 plants m–2 and exhibited linear or quadratic increases in response to increasing cereal density (Table 2). Cut 1 DM yields averaged 8.5, 9.3, 10.2, and 10.5 Mg ha–1 for cereal densities of 30, 60, 90, and 240 plants m–2, respectively. In 3 of 4 yr, protein yields of Cut 1 also increased with increasing cereal density (Table 3). Cut 1 protein yields averaged 1.10, 1.15, 1.26, and 1.26 Mg ha–1 for cereal densities of 30, 60, 90, and 240 plants m–2, respectively.


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  		Table 3. Mean Cut 1 protein yield and Cut 2 dry matter (DM) berseem clover yield for cereal–berseem clover intercrops and berseem clover sole crops (BE) at Edmonton, AB, from 1998 to 2001.

 
The percentage of clover in Cut 1 decreased as cereal density increased, exhibiting quadratic responses (Table 2). The full rate of cereals (240 plants m–2) was very suppressive of berseem clover, with clover components in intercrops of less than 6% by dry weight in 3 of 4 yr. Compared with Cut 1 yields of berseem clover sole crops in 2001, Cut 1 berseem clover DM yield in intercrops was reduced by an average of 83% with 60 cereal plants m–2 and by 94% with 240 cereal plants m–2 (data not shown). In related experiments with berseem clover–oat intercrops, the relationship between berseem clover DM yield and oat plant density at silage stage fit the rectangular hyperbolic model proposed by Cousens (1985) and had steep initial slopes and predicted maximum yield losses of up to 96% (Ross et al., 2003).

Berseem clover regrowth (Cut 2) DM yield was lowest for intercrops with cereal densities of 240 plants m–2 and increased linearly (P < 0.001) as cereal density decreased (Table 3). The effects of cereal competition on berseem clover regrowth varied among years. In 2001, Cut 2 DM yields of intercrops were about 70% less than berseem clover sole crops, indicating substantial effects of cereal competition on clover regrowth. In contrast, Cut 2 DM yields of intercrops were similar to those of berseem clover sole crops in 2000. Thompson and Stout (1997) reported that Cut 2 of barley–Persian clover intercrops equaled that of clover sole crops, indicating that barley had not hindered clover establishment. The recovery of berseem clover from cereal competition may vary with moisture, temperature, and management of companion crops. Cereal companion crops had no effect on subsequent alfalfa (Medicago sativa L.) yields in Minnesota (Simmons et al., 1995), reduced subsequent yields during the establishment year in California (Lanini et al., 1991), and reduced yields in the first 2 yr of alfalfa growth in southern Alberta (Moyer, 1985).

Total season DM yields (total of Cut 1 and Cut 2) for intercrops averaged 12.5 Mg ha–1 for the 3 yr in which two harvests were obtained (Table 4). Cereal density effects on total season DM varied between years. In 1998, there was a linear decrease (P < 0.001) in total season DM yield with increasing cereal density. In 2000 and 2001, there were linear or quadratic (P < 0.05) increases in total season DM yield with increasing cereal density. Carr et al. (1998) found that forage yields of cereal–pea intercrops were significantly reduced with a half-rate of barley or oat. In our study, seeding cereals at 60 or 90 plants m–2 in intercrops generally resulted in equal or higher total season DM and protein yields compared with full cereal rates. Yield compensation in reduced-rate cereal treatments was due to a combination of cereal tillering and greater berseem clover content. The effects of cereal density were most evident in triticale intercrops and were least evident in oat intercrops. For triticale, rates higher than 60 plants m–2 would be recommended for cereal–berseem clover intercrops to maintain silage-stage yields. Jedel and Salmon (1994) noted that triticale forage yields respond positively to higher seeding rates and that optimal forage yield of monocrop triticale may require rates greater than 250 seeds m–2.


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  		Table 4. Mean total{dagger} season dry matter (DM) yield, percentage berseem clover by dry weight of total season yield, and total season protein yield for cereal–berseem clover intercrops and berseem clover sole crops (BE) at Edmonton, AB, in 1998, 2000, and 2001.

 
The effects of cereal density on total protein yield were not significant in 2 of 3 yr (Table 4). In 2000 and 2001, lower total season DM yield at low cereal density was balanced by a greater protein contribution from larger clover components. In 1998, the linear increase in total protein yield with decreasing cereal density reflected increases in both DM yield and clover percentage at lower cereal densities.

Cereal Species Effects on Intercrops
The Cut 1 DM yields of triticale–berseem clover intercrops were greater than those of oat–berseem clover intercrops and barley–berseem clover intercrops in 2 of 4 yr (Table 2). Cut 1 DM yields of oat intercrops were greater than those of barley intercrops in 3 yr. Other studies of cereal intercrops in central Alberta have reported higher yields for oat intercrops than for barley intercrops (Berkenkamp and Meeres, 1987; Jedel and Helm, 1993; Jedel and Salmon, 1994). In this study, Cut 1 DM averaged 9.9 Mg ha–1 for triticale intercrops, 9.7 Mg ha–1 for oat intercrops, and 8.8 Mg ha–1 for barley intercrops.

The percentage of berseem clover in Cut 1 was affected by cereal species in all years (Table 2). Berseem clover Cut 1 components averaged 17% for triticale intercrops, 10% for oat intercrops, and 8% for barley intercrops. The percentage of berseem clover in Cut 1 of triticale intercrops was greater than that of barley intercrops in all 4 yr and greater than that of oat intercrops in 3 yr. The percentage of berseem clover in Cut 1 of oat intercrops was greater than that of barley intercrops in 3 yr. The results for clover component indicate that barley caused greater suppression of berseem clover than did oat or triticale. Similarly, Juskiw et al. (2000b) found that barley was more competitive than oat or triticale in cereal mixtures. Brink and Marten (1986) reported greater competitive effects on alfalfa (Medicago sativa L.) seedlings by barley than oat companion crops. Compared with the Cut 1 DM yield of berseem clover in sole crop treatments, the yields of berseem clover in intercrops were more greatly suppressed by barley and oat than by triticale. Compared with Cut 1 DM yields of berseem clover sole crops in 2000, clover DM yields in intercrops with 60 cereal plants m–2 were reduced by 72 to 73% in barley and oat intercrops and by 56% in triticale intercrops (data not shown). In similar comparisons in 2001, Cut 1 berseem clover DM yield was reduced by 83 to 87% in barley and oat intercrops and by 78% in triticale intercrops. Triticale may have allowed greater light penetration through the canopy than barley or oat. Based on visual determination, Jedel and Helm (1993) observed higher pulse content in intercrops with triticale than with oat or barley.

Regrowth of cereals was negligible in all years except 2001. In 2001, heavy rainfall (146 mm) in mid- to late July caused some flooding and lodging. Tillering in barley can resume after flowering, under conditions of abundant moisture and lodging (Smith et al., 1999). Regrowth of cereals in 2001 averaged 1.1 Mg ha–1 for barley, 0.1 Mg ha–1 for oat, and 1.8 Mg ha–1 for triticale (data not shown).

Berseem clover regrowth (Cut 2) DM yield of barley intercrops was greater than triticale intercrops in 3 yr and greater than oat intercrops in 2 yr (Table 3). Berseem clover regrowth averaged 3.4 Mg ha–1 for barley intercrops, 2.3 Mg ha–1 for oat intercrops, and 2.1 Mg ha–1 for triticale intercrops, for the 3 yr with a Cut 2 harvest. These yields were comparable to berseem clover regrowth reported by Ghaffarzadeh (1997) in Iowa and Stout et al. (1997) in British Columbia. Barley reached silage stage at an earlier date than triticale and oat, making the length of time for clover regrowth 9 to 14 d greater for barley intercrops than for oat and triticale intercrops (Table 1). When triticale and oat intercrops had equal days of regrowth, Cut 2 yields were greater for the triticale intercrops, suggesting less initial suppression of berseem clover by triticale.

Total season DM yields (total of Cut 1 and Cut 2) did not differ among cereal species in 2 of 3 yr (Table 4). Greater Cut 1 yields of oat and triticale intercrops were often balanced by greater Cut 2 yields for barley intercrops. In 2001, total season DM yields of triticale intercrops were greater than those of barley and oat intercrops, and total season DM yields of barley intercrops were greater than those of oat intercrops. The yield differences in 2001 partly reflected different amounts of cereal and berseem clover regrowth. For the 3 yr with two harvests, total season DM yields averaged 12.7 Mg ha–1 for triticale intercrops, 12.6 Mg ha–1 for barley intercrops, and 12.3 Mg ha–1 for oat intercrops.

Total protein yields of barley intercrops were greater than triticale or oat intercrops in all 3 yr (Table 4). Total protein yields of triticale intercrops were greater than oat intercrops only in 2001. For the 3 yr with two harvests, total protein yields averaged 1.91 Mg ha–1 for barley intercrops, 1.66 Mg ha–1 for triticale intercrops, and 1.59 Mg ha–1 for oat intercrops. The percentage of berseem clover in total yield averaged 34% for barley and triticale intercrops and 28% for oat intercrops. Higher total protein yields for barley intercrops reflected a combination of relatively high CP for barley and substantial regrowth of high quality berseem clover.

Berseem clover had better forage quality than cereals at Cut 1, with 40 to 55 g kg–1 higher CP and 100 to 185 g kg–1 lower NDF (Table 5). The CP of barley intercrops at Cut 1 silage stage was greater than that of oat or triticale intercrops. Jedel and Helm (1993) found that the CP of barley intercropped with pulses was higher than that of oat intercrops but similar to triticale intercrops.


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  		Table 5. Mean{dagger} crude protein (CP), acid detergent fiber (ADF), and neutral detergent fiber (NDF) concentrations for cereals and berseem clover for Cut 1 and Cut 2 of cereal–berseem clover intercrops at 60 cereal plants m–2 and berseem clover sole crops (BE) at Edmonton, AB, for 1998, 2000, and 2001.

 
Berseem clover regrowth (Cut 2) had high forage quality, with mean CP of 210 g kg–1, ADF of 215 g kg–1, and NDF of 310 g kg–1 (Table 5). There were few differences in berseem clover quality among treatments. The ADF of the berseem clover regrowth in oat and triticale intercrops was lower than that of the somewhat older regrowth in barley intercrops.

We tested one cultivar each of barley, oat, and triticale. Cultivars of barley and oat differ in their competitiveness in intercrops (Holland and Brummer, 1999; Juskiw et al., 2000b). Additional study with barley, oat, and triticale cultivars in intercrops would further substantiate the differences among the three cereal species in intercrops.

Berseem Clover Sole Crops versus Intercrops
The DM yields of berseem clover sole crops (BE 1 and BE 2) were an average of 43% less than Cut 1 intercrop yields and were greater than or equal to Cut 2 intercrop yields (Tables 2 and 3). Total season DM yields of berseem clover sole crops were less than intercrop yields in 2001 but did not differ from intercrops in 2000 (Table 4). In 1999, when berseem clover regrowth was negligible, the total season yield of berseem clover sole crops was much less than that of intercrops.

Higher DM yields for intercrops than for berseem clover sole crops have been reported in other studies of berseem clover–cereal intercrops (Welty et al., 1991; Holland and Brummer, 1999). In our study, intercrops provided greater midseason forage and greater yield stability than berseem clover sole crops. However, the yield potential of berseem clover was demonstrated by high total yields in 2000. Growing berseem clover as a monocrop might be preferable where the emphasis is on providing high quality late-season grazing. Forage conservation would likely be easier with berseem clover–cereal intercrops than with berseem clover sole crops. The cereal component would counter problems that may occur with sole crop berseem clover, including lodging, high moisture content, and capacity to buffer the acid production required for silage preservation. Inclusion of a companion grass with legumes can provide a more balanced chemical composition for ensiling (Laidlaw and McBratney, 1980).

Potential of Cereal–Berseem Clover Intercrops
Cereal–berseem clover intercrops produced high forage yields, with cereals as the dominant component. Intercrop DM yields were greater than or equal to other reports for cereal–legume intercrops in central Alberta of 6.6 to 12.3 Mg ha–1 (Berkenkamp and Meeres, 1987) and 8 to 11 Mg ha–1 (Jedel and Helm, 1993) for oat, barley, or triticale intercropped with pea or fababean (Vicia faba L.) and 8.9 Mg ha–1 for barley–pea intercrops (Izaurralde et al., 1993).

Early or concurrent emergence of berseem clover, relative to cereals, increased the berseem clover component in intercrops. Relatively small berseem clover components in intercrops, of about 20%, caused some improvement in Cut 1 silage-stage forage quality (Table 5). The NDF for intercrops with 60 cereal plants m–2 was 25 to 45 g kg–1 lower than for cereals alone, indicating improved forage intake potential. There was a trend of higher CP for intercrops than for cereals alone. Other intercrop studies have reported a greater impact of legumes on forage quality. Chapko et al. (1991) reported that adding pea to oat or barley increased CP by 44 and 30 g kg–1 and decreased NDF by 71 and 62 g kg–1, respectively. The addition of berseem clover to a barley–ryegrass mixture substantially increased the CP of the Cut 1 harvest (Stout et al., 1997). In our study, high initial soil N levels may have reduced the impact of berseem clover on intercrop CP. The CP of the cereals (105 to 140 g kg–1) was relatively high. Lower CP concentrations have been reported in other studies of silage cereals in central Alberta: 60 to 100 g kg–1 CP for oat, barley, and triticale (Juskiw et al., 2000a) and 90 to 125 g kg–1 CP for barley and triticale (Jedel and Salmon, 1995). Carr et al. (1998) found that intercropping pea with oat or barley did not increase forage CP in high-soil-N environments but did increase CP in low-soil-N environments.

Berseem clover regrowth (Cut 2) yields were highest under conditions of above-average seasonal temperatures, early silage-stage harvest, and adequate moisture following Cut 1. For the 3 yr with a Cut 2 harvest, berseem clover regrowth averaged 2.6 Mg ha–1 DM. These yields compare well with cereal regrowth of 0.05 to 2.39 Mg ha–1 DM, after silage harvest, for intercrops of spring and winter cereals in central Alberta (Jedel and Salmon, 1995).

The greatest advantage of berseem clover–cereal intercrops may be the clover regrowth after silage harvest. Berseem clover regrowth has potential to increase the total productivity of land and reduce the cost of production. The high N content of berseem clover regrowth could provide forage and soil benefits. Late-season clover regrowth would supply high quality forage at a time when forage quality and quantity is often limited. From the perspective of soil benefits and sustainability, plowdown of clover regrowth could increase soil N, reduce fertilizer requirements, and improve soil quality.


   SUMMARY AND CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 SUMMARY AND CONCLUSIONS
REFERENCES
 
Performance of cereal–berseem clover intercrops was influenced by cereal species, cereal density, relative emergence, and environmental conditions. Intercrops with AC Lacombe barley had advantages of earliness, greater Cut 2 yield, and greater total protein yield. Intercrops with Pronghorn triticale and Waldern oat had greater Cut 1 silage-stage yield, with a greater berseem clover component. In response to increasing cereal density, Cut 1 DM yield increased, percentage of berseem clover in Cut 1 decreased, and Cut 2 DM yield decreased. Reducing cereal seeding rates to 60 to 90 plants m–2 (25 to 40% of full rate) usually improved forage quality without reducing total season yield. Seeding of the intercrop must ensure that berseem clover emerges before or with the cereals. Early silage harvest is recommended to increase the yield of berseem clover regrowth for fall pasture. On highly productive soils, the main benefit of cereal–berseem clover intercrops may be the addition of high quality late-season forage.


   ACKNOWLEDGMENTS
 
The technical assistance of W. Kassa, N. Preikschat, R. Davy, C. Martin, J. Walker, L. Danforth, S. Schattle, G. Rawluk, G. Su, J. Zhao, and J. Deeks is gratefully acknowledged. Our thanks to P. Juskiw and the late S. Kibite for advice on barley and oat cultivars. We also acknowledge the financial support of the Alberta Agriculture Research Institute and the Canadian Wheat Board scholarship program.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 SUMMARY AND CONCLUSIONS
 REFERENCES
 




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