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a Dep. of Agric., Food, and Nutritional Sci., 4-10 Agriculture-Forestry Cent., Univ. of Alberta, Edmonton, AB, Canada T6G 2P5
b Alberta Agric. and Food, Agric. Res. Division, Barrhead, AB, Canada T7N 1A4
c Agric. and Agri-Food Canada, Lacombe Res. Cent., 6000 C & E Trail, Lacombe, AB, Canada T4L 1W1
* Corresponding author (sheryl{at}ualberta.ca).
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ABSTRACT |
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 TOPNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARY AND CONCLUSIONSREFERENCES |
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Abbreviations: ADF, acid detergent fiber • ADL, acid detergent lignin • CP, crude protein • DM, dry matter • LPD, legume planting density • NDF, neutral detergent fiber • RFV, relative feed value
a Dep. of Agric., Food, and Nutritional Sci., 4-10 Agriculture-Forestry Cent., Univ. of Alberta, Edmonton, AB, Canada T6G 2P5
b Alberta Agric. and Food, Agric. Res. Division, Barrhead, AB, Canada T7N 1A4
c Agric. and Agri-Food Canada, Lacombe Res. Cent., 6000 C & E Trail, Lacombe, AB, Canada T4L 1W1
* Corresponding author (sheryl{at}ualberta.ca).
Received for publication June 5, 2007.
Annual cool-season grain legumes grown in mixtures with barley (Hordeum vulgare L.), may offer advantages over barley sole crops for forage production. Our objective was to evaluate the effects of intercropping ‘Snowbird’ tannin-free faba bean (Vicia faba L.), ‘Arabella’ narrow-leafed lupin (Lupinus angustifolius L.), and ‘Cutlass’ field pea (Pisum sativum L.), along with legume planting densities (LPD) on forage yields, nutritive value, and economic returns. Field studies were conducted at three sites in the Parkland region of Alberta, Canada, in 2004 and 2005. Each legume was planted at 0.5, 1.0, 1.5, and 2.0x their recommended sole crop planting density with ‘Niobe’ barley at 0.25x the recommended sole crop planting density. A barley sole crop was also included for comparison. Increasing the LPD from 0.5 to 2.0x did not effect forage dry matter (DM) but it increased the proportion of legume in the forage DM from 39 to 63%, protein concentration from 119 to 132 g kg–1, and acid detergent lignin (ADL) from 36 to 42 g kg–1 while it decreased neutral detergent fiber (NDF) from 465 to 422 g kg–1. Faba bean–barley, lupin–barley, and pea–barley intercrops had 64, 27, and 55% higher protein yields, respectively, compared to sole crop barley. Faba bean–barley and lupin–barley had similar forage DM yields which were 1.5 Mg ha–1 and 1.3 Mg ha–1 less than pea–barley and sole barley crops, respectively. Intercrops of Cutlass pea and Niobe barley offered the most favorable combination of forage DM yields, nutritive value, and economic returns.
Abbreviations: ADF, acid detergent fiber • ADL, acid detergent lignin • CP, crude protein • DM, dry matter • LPD, legume planting density • NDF, neutral detergent fiber • RFV, relative feed value
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INTRODUCTION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARY AND CONCLUSIONSREFERENCES |
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Intercrops of multiple cereal species have been tested for forage potential in western Canada. Baron et al. (1992) found the nutritive value of spring–winter cereal mixtures to be consistently superior to sole spring crops. Jedel and Salmon (1994) reported yield stability and increased nutritive value in triticale (xTriticosecale spp.)–barley and triticale–oat (Avena sativa L.) mixtures compared to cereal sole crops. Juskiw et al. (2000) reported that various mixtures of barley, oat, triticale, and rye (Secale cereale L.) displayed extended harvest periods and had better forage nutritive value, as measured by NDF and acid detergent fiber (ADF), compared with sole crops.
The inclusion of grain legumes in forage intercrops can provide a more sustainable source of N to cropping systems through biological N fixation (Crews and Peoples, 2004). Intercropping legumes with cereals may also minimize N losses commonly associated with legume sole crops through uptake of soil inorganic N by the cereal and slower N mineralization during decomposition, due to higher cereal C/N ratios (Hauggaard-Nielsen et al., 2003). In previous studies, the inclusion of grain legumes in forage intercrops has increased protein yields (Walton, 1975; Berkenkamp and Meeres, 1987; Anil et al., 1998), and improved forage nutritive value (Chapko et al., 1991; Carr et al., 1998).
Traditionally, field pea has been the only grain legume crop grown in the Parkland region of Alberta, Canada. However, since 2002 tannin-free faba bean production has increased due to its lack of anti-nutritional factors, high energy, high protein, high yields, and similar production costs relative to field pea. A second cool-season grain legume crop, low-alkaloid, narrow-leafed lupin is also showing promise as a new crop in the region. Previous studies conducted in the United Kingdom (UK), reported narrow-leafed lupin whole crop forage DM yields of 6.6 to 8.4 Mg ha–1 and crude protein (CP) concentrations more than 190 g kg–1 DM (Fraser et al., 2005). By comparison, maximum faba bean and pea forage DM yields and CP concentrations of 7.8 and 6.2 Mg ha–1 and 180 and 157 g kg–1, respectively, were reported in the UK (Fraser et al., 2001). The moderate yields and high CP concentrations of these grain legume crops make them candidates for inclusion in legume–barley forage intercrops.
Although pea–cereal intercrops have been frequently studied (Berkenkamp and Meeres, 1987; Chapko et al., 1991; Jedel and Helm, 1993; Carr et al., 1998, 2004; Mustafa and Seguin, 2004) few studies have tested faba bean–cereal (Berkenkamp and Meeres, 1987; Jedel and Helm, 1993; Ghanbari-Bonjar and Lee, 2003) or lupin–cereal intercrops (McKenzie and Spaner, 1999; Carruthers et al., 2000; Azo et al., 2006). We are not aware of any previous studies that have compared these three cool-season grain legume species grown in mixtures with cereals.
Legumes are often less competitive than cereal species and may require higher planting densities relative to cereals to achieve intercropping benefits. Carr et al. (1998) tested three pea planting densities (40, 80, 120 seeds m–2) in intercrop combinations with various planting densities of barley and oat (93, 185, 278 seeds m–2) for forage production. Due to the high cereal densities, no significant DM or N yield benefits were observed as the intercrops were heavily dominated by the cereal component. In intercrop studies for grain production, Izaurralde et al. (1990) tested three pea planting densities (25, 50, 75 plants m–2) with three barley planting densities (86, 172, 258 plants m–2). Grain, straw, and DM yields of intercropped mixtures increased with increasing the pea planting density. Different trends in the above studies may be related to the competitiveness of the species and varieties used in each study.
The objective of this study was to determine the feasibility of faba bean–barley, lupin–barley, and pea–barley intercrops for forage production in the Parkland region of Alberta, Canada. Two questions were being addressed. Are grain legume–barley forage intercrops a viable option for producers in the Parkland region of Alberta, Canada, compared to traditional barley sole crops for forage production? Which grain legume species and planting densities maximize forage DM yield, nutritive value, and economic returns in an intercrop forage system?
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MATERIALS AND METHODS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARY AND CONCLUSIONSREFERENCES |
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Experimental Design and Plot Management
Treatments in this study were a subset of treatments from a larger study. The experimental design for the current study was a split-plot randomized complete block design with four blocks. Legume species was the main plot and legume planting density (LPD) was the subplot. Barley sole crops were included in the experimental design of the current study. Snowbird tannin-free (11 g tannin kg–1 seed) faba bean, Arabella low-alkaloid (200 mg alkaloids kg–1 seed) narrow-leafed lupin, and Cutlass field pea were intercropped with Niobe barley. Barley was planted at right angles to the legume, and seeded at 0.25x (53 plants m–2) the recommended barley sole crop target plant population (210 plants m–2) to create legume–barley intercrops. The barley planting density was selected in attempts to create an intercrop that was not heavily dominated by either species. Legume planting densities represented 0.5, 1.0, 1.5, and 2.0x the recommended sole crop plant population for each legume species in the Parkland region of Alberta, Canada. Recommended populations for faba bean, lupin, and pea are 45, 100, and 75 plants m–2, respectively (Alberta Agriculture and Food, 2001). The barley sole crop was seeded to meet the recommended target plant population of 210 plants m–2 (Alberta Agriculture and Food, 2001) and represented the typical cereal forage crop grown in the Parkland region of Alberta, Canada (Alberta Agriculture and Food, 2006). Mean faba bean emergence was 98% of expected (range 77–123%), mean lupin emergence was 76% of expected (range 36–132%), mean pea emergence was 97% of expected (range 82–117%), mean barley emergence was 70% of expected (range 52–83%). This resulted in pea–barley and faba bean–barley intercrops having a slightly higher legume content than was initially intended.
Experiments were seeded 3 May 2004 and 4 May 2005 at Barrhead, 4 May 2004 and 2 May 2005 at Devon, and 13 May 2004 and 3 May 2005 at Lacombe. Individual subplots were 2.4 by 6 m. Legumes were seeded in 12 rows with a small-plot-hoe drill at 20-cm row spacing. For each legume species, peat-based-granular inoculant, containing the appropriate Rhizobium bacteria, was placed in the furrow. All legumes were seeded at the same depth, with actual depths varying between 5 and 7.5 cm, depending on soil moisture conditions. Immediately after seeding the legume, barley was cross-seeded with a 3.05-m wide hoe-press drill (Model 9450, John Deere, Deere and Company, Moline, IL) at a depth of 2 to 3.5 cm and a row spacing of 17.5 cm, which did not interfere with legume seed placement.
Phosphorous (triple superphosphate), K (potassium chloride), and S (elemental sulfur) were applied to all treatments in the spring based on soil test recommendations for a 4.57 Mg seed ha–1 pea grain crop. To avoid negative effects of fertilizer applications on seedling emergence, up to 118 kg ha–1 fertilizer was side-banded 2.5 cm from the seed row. If fertilizer recommendations exceeded this, the remaining fertilizer was broadcast and incorporated with harrows.
Before seeding in 2004, triallate [S-(2,3,3-trichloroallyl) diisopropylthiocarbamate] at 1.7 kg a.i. ha–1 was applied and appropriately incorporated to control wild oat (A. fatua L.) in all site years with the exception of Lacombe, where glyphosate [N-(phosphonomethyl)glycine] at 440 g a.i. ha–1 was applied to control early emerged weeds. To control heavy weed pressure at Devon, glyphosate at 440 g a.i. ha–1 and MCPA [(4-chloro-2-methylphenoxy)acetic acid] at 300 g a.i. ha–1 were applied before crop emergence. After crop emergence, broadleaf weeds in the faba bean–barley, pea–barley, and sole crop barley were controlled with an initial application of bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] at 1.1 kg a.i. ha–1 in 240 L ha–1 of water at 275 kPa when the legumes were at the three to four node stage. At Devon and Barrhead, there were no in-crop herbicide applications on lupin. At Lacombe, metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] was applied at 230 g a.i. ha–1 with a water volume of 240 L ha–1 at 275 kPa 2 wk after bentazon, on all treatments. In 2005, broadleaf weeds were controlled with two applications of metribuzin at 230 g a.i. ha–1 with a water volume of 240 L ha–1 at 275 kPa, 10 d apart. At Lacombe only one metribuzin application was made. At all sites wild oat was controlled with an application of tralkoxydim (2-[1-(ethoxyimino)propyl]-3-hydroxy-5-(2,4,6-trimethylphenyl)-cyclohex-2-enone) at 198 g a.i. ha–1 with a water volume of 240 L ha–1 at 275 kPa three to 5 d after the first metribuzin application. In both years, subsequent weed flushes were hand-weeded. Although the herbicide applications made in this study present a source of variability, there is no single, in-crop, broadleaf herbicide that is registered for use on all three grain legume species. It should be noted that previous studies found that post emergent applications of metribuzin had no negative effects on lupin, but in faba bean caused height reductions and some leaf burn which did not result in a significant seed yield reduction (D. Cole, personal communication, Alberta Agriculture and Food, Edmonton, AB, 2005).
Total forage DM yields were measured when barley reached the silage stage (soft dough). This corresponded to 28 July 2004 and 4 Aug. 2005 at Barrhead, 3 Aug. 2004 and 2005 at Devon, and 9 Aug. 2004 and 26 July 2005 at Lacombe. The harvested sample was hand-cut at a height of 5 cm above the soil surface. In 2004, forage yield was sampled from two 0.4-m2 quadrats, which had been marked after emergence. In 2005, forage yield was sampled by hand-cutting a 0.5-m strip from each plot resulting in a harvested area of 1.2 m2. The harvested biomass was separated into legume and barley, dried at 40°C, and weighed to determine forage yield. Samples of each species were ground with a Wiley mill to 1 mm and then analyzed for forage nutritive value. Nitrogen was determined using a LECO N-analyzer (Model CN-2000, Leco Corp., St Joseph, MI) and multiplied by 6.25 for CP. The NDF, ADF, and ADL analyzes were conducted using batch procedures outlined by ANKOM Technology Corporation (Fairport, NY) for an ANKOM200 Fiber Analyzer (Komarek, 1993; Komarek et al., 1994). Relative feed value (RFV) was calculated from ADF and NDF concentrations using the equations presented in Albrecht and Hall (1995).
Data Analysis
All data were tested for normality using PROC UNIVARIATE (SAS Institute, 2003). The analysis indicated that transformations were necessary for some data. Total yield, proportion of legume in the total yield, CP, and ADL were log10 (x + 1) transformed while the protein yield was square root transformed (x0.5). Acid detergent fiber and NDF data did not require transformation.
A preliminary analysis of variance indicated that forage DM yields were significantly different between site years (P < 0.0001) with yields at Devon 2004 = Barrhead 2004 > Barrhead 2005 = Devon 2005 > Lacombe 2005 > Lacombe 2004. Higher yields were associated with sites receiving higher rainfall and having higher spring soil moisture. Growing environment (site x year) was considered to be a random effect as sites were selected to represent the Parkland region of Alberta, Canada and climatic conditions throughout the study were typical for the area. Therefore, analyses of variance were performed using data combined across environments (site x year) with the MIXED procedure of SAS (Littell et al., 2006). Legume species and LPD were considered fixed effects. The ADF and ADL data was analyzed with the NOBOUND option of PROC MIXED to get better control over Type I error and improve power as the Block x Legume(SiteYr) variance component was zero without this option (Littell et al., 2006).
Legume planting density effects (n = 4) were separated with orthogonal polynomial contrasts, using coefficients derived in the IML procedure of SAS. Single degree of freedom contrasts were performed to detect significant differences in forage DM yield and forage nutritive value between the barley sole crop, and the three legume–barley intercrops. Comparisons were also made between the three legume–barley intercrops. A significance level of P 
0.05 was used for all statistical tests.
A simple economic analysis was conducted to determine the economic returns associated with intercropping legumes with barley for forage production based on the increased seeding costs and the resulting forage yield and nutritive value. Seed costs were obtained from a pedigreed-seed grower in the Barrhead area (R. Mueller, personal communication, Richard's Pedigreed Seed, Barrhead, AB, 2007). The cost of lupin seed was assumed to be equal to the price of faba bean seed. Feed grain prices at Barrhead in mid-February 2007 were used to determine forage values (L. Hein, personal communication, Champion Feed Services Ltd., Barrhead, AB, 2007). The silage pricing formula was obtained from Alberta Agriculture and Food (2004) to calculate the value of barley forage as:
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RESULTS AND DISCUSSION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARY AND CONCLUSIONSREFERENCES |
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Crude Protein Concentrations
All legume–barley intercrops had higher CP concentrations relative to the sole barley crop (Table 2). Averaged across all legume–barley intercrops, intercrops had a 62% higher CP concentration compared to sole barley. This can be attributed to inheritantly higher CP concentrations of the legumes and higher CP concentrations of the barley in the intercrop compared to the sole crop. Sole crop barley had a CP concentration of only 79 g kg–1 (Table 2) but the barley component of the faba bean, lupin, and pea intercrops had a 108, 92, and 100 g kg–1 CP concentration (data not shown), respectively. The increased CP concentration of intercropped barley has been attributed to N sparing by the legume resulting in high soil N levels for the non-legume (Vest, 1971), increased light, water, and nutrient uptake (Willey, 1979b), and possibly the transfer of fixed N from the legume to the non-legume (Eaglesham et al., 1981; Vasilas and Ham, 1985).
The CP concentration differed among intercrops (Tables 2 and 3). Faba bean–barley intercrops had the highest CP concentration (145 g kg–1), followed by pea–barley (127 g kg–1), and then lupin–barley (112 g kg–1) intercrops. Ghanbari-Bonjar and Lee (2003) reported a CP concentration of 110 g kg–1 for a faba bean–wheat (Triticum aestivum L.) intercrop planted and harvested under similar conditions as our study. The reported CP of pea–barley forage intercrops range from 122 g kg–1 (Mustafa and Seguin, 2004) to 147 g kg–1 (Carr et al., 2004). Azo et al. (2006) reported CP concentrations of 101, 143, and 186 g kg–1 for lupin–triticale, lupin–wheat, and lupin–millet [Pennesitum americanum (L.) Leeke] forage intercrops, respectively. Forage nutritive value can be expected to vary depending on cultivar, agronomic practices, environmental conditions during growth (Juskiw et al., 2000), and the proportion of legume in intercrop mixtures, making direct comparisons between studies difficult.
Nutritive Value
Forage nutritive value, as indicated by the RFV, was improved in all legume–barley intercrops relative to the sole barley crop (Table 2). The lower barley sole crop RFV was attributed to the higher NDF and ADF concentrations in the sole crop barley compared to the legume–barley intercrops. Other authors have also reported higher NDF concentrations in sole crop barley relative to pea–barley intercrops (Chapko et al., 1991; Carr et al., 2004; Aasen et al., 2004). Of the legume–barley intercrops, pea–barley intercrops had the highest RFV (151), followed by faba bean–barley intercrops (143), while lupin–barley intercrops had the lowest RFV (132). Differences in RFV between legume species were attributed to differences in NDF, as ADF was similar between legume species. In central Alberta, Canada, Jedel and Helm (1993) also found no differences between the ADF concentration of faba bean–cereal and pea–cereal intercrops.
In agreement with Waldo and Jorgensen (1981), we found the ADL concentrations of faba bean–barley and pea–barley intercrops were greater than the ADL concentration of sole crop barley (Table 2). This can be attributed to higher lignin concentration of legumes compared to cereals (Waldo and Jorgensen, 1981). Although legume–barley forage contains more lignin than sole barley, Van Soest (1964) reported that alfalfa (Medicago sativa L.) had a higher lignin concentration than grasses, but they had equal digestibility. These findings warrant further investigation of the fiber digestibility of these legume–barley intercrops. The higher ADL concentration of faba bean–barley and pea–barley intercrops compared to lupin–barley intercrops (Tables 2 and 3) was due to proportionately more legume in the faba bean and pea intercrops than the lupin intercrops.
Protein Yield
One of the main advantages of legume–cereal forage intercrops has been increased protein yield, relative to cereal sole crops (Walton, 1975; Berkenkamp and Meeres, 1987; Izaurralde et al., 1990; Aasen et al., 2004; Carr et al., 2004). There was a significant legume species by LPD interaction for protein yield (Table 3), but this was attributed primarily to much lower lupin–barley protein yields (1.4 Mg ha–1) compared to faba bean–barley (1.8 Mg ha–1) and pea–barley intercrops (1.7 Mg ha–1) (Table 2). We observed 48% higher protein yields for legume–barley intercrops, on average, compared to the barley sole crop (Table 2). This was attributed to legume–barley intercrops having 62% higher CP concentrations, on average, relative to sole barley crops.
The highest protein yields were achieved with faba bean–barley and pea–barley intercrops (Tables 2 and 3). Although pea–barley and faba bean–barley intercrops had similar protein yields, it was achieved with different strategies. Faba bean–barley intercrops produced high protein yields due to the high CP concentration of each component (faba bean 176 g kg–1; intercropped barley 108 g kg–1) (data not shown). Pea–barley intercrops produced high protein yields due to a high forage DM yield and a high proportion of legume in the forage DM. Carr et al. (1998) noted that increasing intercrop protein yield required a significant proportion of legume DM in the intercrop mixture.
Legume Planting Density Effects
All measured parameters were affected by LPD, with the exception of total forage DM yield and ADF (Table 3). Proportion of legume, CP, and ADL increased, following a quadratic trend, while protein yield increased following a cubic trend, as LPD increased. As LPD increased, NDF decreased following a linear trend.
There was a trend (P = 0.07) for greater forage DM yields at higher LPD, and a significant quadratic trend (P = 0.03) indicated maximum forage DM yields at the 1.5x LPD (Table 3). Mean forage DM yields, averaged over all species, were 12.3, 12.4, 12.7, and 12.5 Mg ha–1 for intercrops with LPDs of 0.5, 1.0, 1.5, and 2.0x, respectively. Lower forage DM yields at the 0.5x and 1.0x LPD indicated that there were too few plants to use all the available resources in the system. At the 1.5x LPD, maximum intercrop yields occurred and maximum resource consumption was thought to be occurring. Forage yield decreased at the 2.0x LPD indicating increased competition at higher total plant populations.
Averaged over all species, the proportion of legume in the forage DM was 39, 51, 59, and 63% for intercrops with LPDs of 0.5, 1.0, 1.5, and 2.0x, respectively. Doubling the LPD from 1.0 to 2.0x increased the proportion of legume in the forage DM by only 24%. In Alberta, Canada, Izaurralde et al. (1990) also found that doubling the pea planting density increased intercropped pea DM yields by only 46%, indicating that legume yield was not directly proportional to the LPD.
Many of the forage nutritive value responses to increasing LPD can be explained by the increased proportion of legume in the forage DM. Compared to barley, legume species had higher CP, lower NDF, and higher ADL (data not shown). Therefore, as the proportion of legume in the forage DM increased, CP increased, NDF decreased, and ADL increased resulting in improved forage nutritive value. The increased protein yield in response to increased LPD may also be attributed to the increasing proportion of high protein legume in the intercrop DM.
Carr et al. (1998) examined forage DM and N yield of pea–cereal intercrops in North Dakota. Different trends between our study and Carr et al. (1998) may be attributed to higher cereal planting densities (93, 185, and 278 kernels m–2) used by Carr et al. (1998) compared to the target barley plant population of 53 plants m–2 used in our study. As a result, Carr et al. (1998) found the cereal component dominated the intercrop which may explain why they observed no increase in forage DM or N yield as the intercropped-pea seeding rate increased. However, Carr et al. (1998) still found that the CP concentration of cereal–pea forage increased as the pea seeding rate increased. They concluded that the CP concentration of cereal–pea forage increased as the proportion of sown pea seeds to sown cereal kernels increased but forage N yield was unaffected by intercropping as the cereal component contributes more to yield than the pea component.
Economic Analysis of Intercropping
The increased seeding costs associated with the legume component of legume–barley intercropping relative to sole barley cropping can only be justified if intercrop yields are similar to or greater than sole barley, and nutritive value is improved. Aasen et al. (2004) compared the economic suitability of sole barley cropping and pea–barley intercropping for forage production. Based on 1998 costs, they determined input costs to be $140 ha–1 for barley sole crops and $190 to $202 ha–1 for pea–barley intercrops. They concluded that small improvements in the nutritive value of the pea–barley mixture was not enough to off-set the increased costs of mixed cropping relative to sole cropping. However, their study did not attempt to determine a dollar value for the higher nutritive value forage, or costs for supplementing lower nutritive value feed, which might have altered their conclusions.
In our study, mean economic returns were $983, $939, $1188, and $1009 ha–1 and mean seed costs were $120, $102, 100, and $30 ha–1 for faba bean–barley, lupin–barley, pea–barley, and sole barley crop forage, respectively (Table 4 ). The high economic returns for pea–barley relative to the other legume–barley mixtures can be attributed to lower pea seed costs and higher legume forage DM yields. Pea–barley forage was the only mixture to have better economic returns than a sole barley crop, which was primarily attributed to the higher feed value of the legume DM relative to barley DM. Legume planting density and the legume species x LPD interaction had no effect on economic returns.
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Operational costs (time, fuel, equipment) associated with N fertilizer applications in a barley sole crop are replaced by the operational costs associated with planting the legume in the legume–barley intercrop, so we did not include these factors in the economic analysis. Our cost analysis did not include N fertilizer and application costs for sole barley crops, legume inoculant costs, herbicide costs, yield and price fluctuations, climatic factors, or the value of alternative forages, but it appears that the increased forage yield and nutritive value of pea–barley intercrops may be economically beneficial. Economic returns from the intercrops could be further increased if the value of improved yield stability, enhanced nutrient use, and improved weed, insect, or disease control associated with intercropping, were factored into the analysis.
Potential of Legume–Barley Intercrops
The legume–barley intercrops tested in this study produced forage DM yields between 11.8 to 13.8 Mg ha–1 which were similar to, or greater than, annual legume–cereal forage DM yields reported in other studies conducted in central Alberta, Canada of 6.6 to 12.3 Mg ha–1 (Berkenkamp and Meeres, 1987), and 8 to 11 Mg ha–1 (Jedel and Helm, 1993). Yields were also comparable with sole barley crop forage yields (10.1–16.5 Mg ha–1) in the northern Prairies (Juskiw et al., 2000). Forage yields of pea–barley intercrops were equivalent to barley sole crops and therefore do not present a yield disadvantage to producers.
The greatest advantage of legume–barley forage intercrops was improved nutritive value relative to barley sole crops. Based on RFV, legume–barley forage intercrops had similar nutritive value to alfalfa at pre-bloom or early-bloom stage, while barley forage sole crops had similar nutritive value to alfalfa at mid-bloom (Rohweder et al., 1978). These intercrops offer the opportunity to produce annual forage with comparable nutritive value to perennial alfalfa. Annual legume–barley intercrops also do not have establishment and persistence difficulties associated with perennial alfalfa. In the absence of N fertilizer, legume–barley forage intercrops produced high CP concentrations and protein yields. The increased value associated with improved nutritive value resulted in a greater economic return for the pea–barley forage compared to the barley sole crop forage.
In addition to comparable sole barley crop forage yields and superior nutritive value, legume–barley intercrops increased cropping system diversity and supported biological N fixation. Increased cropping system diversity can improve nutrient cycling, regulate local hydrological processes, reduce pest populations, and detoxify noxious chemicals (Altieri, 1995). Legume–barley forage intercrops, which fix atmospheric N to meet their N requirements, have the added advantage of eliminating N fertilizer from production costs and may provide N and non-N benefits to subsequent crops. However, more work is needed to better understand the N and non-N benefits of incorporating legume–cereal intercrops into rotations with sole crops.
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SUMMARY AND CONCLUSIONS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARY AND CONCLUSIONSREFERENCES |
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Increasing the LPD from 0.5 to 2.0x had no affect on forage DM production or economic returns, but CP concentration, ADL concentration, and proportion of legume in the forage DM increased, while NDF decreased. Unlike some previous studies, we were able to consistently achieve improved nutrient values by growing legume–cereal intercrops that were not heavily dominated by the cereal species. This can be attributed to the relatively low barley seeding rate (53 plants m–2) used in this study. Further study is required to assess the feed value and ensiling potential of grain legume–barley intercrops.
Grain legume–barley forage intercrops are a viable option for producers in the Parkland region of Alberta, Canada, compared to barley sole crops. Their greatest attributes were high CP concentrations, protein yields, and RFVs. With comparable nutritive value to bud to early bloom alfalfa, annual grain legume–barley intercrops may be an alternative to perennial alfalfa.
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ACKNOWLEDGMENTS |
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NOTES |
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