Fermentability and Nutritive Value of Corn and Forage ...

RESEARCH

Fermentability and Nutritive Value of Corn and Forage Sorghum Silage When in Mixture with Lablab Bean Francisco Contreras-Govea,* Mark Marsalis, Sangamesh Angadi, Gerald Smith, L. M. Lauriault, and Dawn VanLeeuwen ABSTRACT Intercropping legumes with nonlegume crops has shown benefits in improving dry matter (DM) yield, but additional information is needed when crop mixtures are ensiled. This study assessed the fermentation characteristics of forage corn silage (Zea mays L.) (CS) and forage sorghum silage [Sorghum bicolor (L.) Moench] (FS) when mixed with different proportions of lablab bean [Lablab purpureus (L.) Sweet] (LB). Corn, FS, and LB were grown in separate fields at two locations in 2009. At each location, crops were cut and chopped separately and taken to the laboratory for ensiling. Six mixtures were handmade on a percentage fresh weight basis for each CS–LB and FS–LB combination, including (i) 100:0, (ii) 90:10, (iii) 75:25, (iv) 50:50, (v) 25:75, and (vi) 0:100. For each mixture, a 1-L glass jar (mini-silo) was filled with 500 g of fresh material, with four jars per treatment. Forage in mini-silos was fermented for 60 d at room temperature (25°C). Analysis was conducted for nutritive value and fermentation characteristics. The greatest impact of mixing LB with CS or FS was on crude protein (CP) and acid detergent fiber (ADF) concentrations, with no significant impact on neutral detergent fiber (NDF). Averaging across CS and FS, CP concentration increased from 87 to 173 g kg−1 and ADF concentration from 253 to 306 g kg−1 as LB increased from 0 to 75% in the mixture. Increasing LB in the mixture also increased other constituents, such as pH and lactic and acetic acid concentrations. Adding LB to CS or FS for silage can have a positive effect on the final nutritive value, but additional research is needed to assess the impact in cattle.

F.E. Contreras-Govea, New Mexico State University, Agricultural Science Center at Artesia, 67 E. Four Dinkus Road, Artesia, NM 88210; M.A. Marsalis and S.V. Angadi, New Mexico State University, Agricultural Science Center at Clovis, 2346 State Road 288, Clovis, NM 88101; G.R. Smith, Texas A&M University System, Texas AgriLife Research and Extension Center at Overton, 1710 FM 3053 N., Overton, TX 75684; L.M. Lauriault, New Mexico State University, Agricultural Science Center at Tucumcari, 6502 Quay Road AM 5, Tucumcari, NM 88401; D.M. VanLeeuwen, Agricultural Biometrician, New Mexico State University, Las Cruces, NM 88003. Received 18 May 2010. Corresponding author ([email protected]). Abbreviations: ADF, acid detergent fiber; CP, crude protein; CS, corn silage; DM, dry matter; FS, forage sorghum silage; IVTDMD, in vitro true dry matter digestibility; L:A, lactate:acetate; LB, lablab bean; NDF, neutral detergent fiber; NDFD, neutral detergent fiber digestibility; TDN, total digestible nutrients; WSC, water soluble carbohydrates.

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ustainability and profitability of agricultural systems have been continuous goals throughout the world. Intercropping legumes with nonlegume crops has shown benefits in improving dry matter (DM) yield and forage nutritive value (Dawo et al., 2007), but information on fermentation profiles is needed when intercropped forage is ensiled. Increasing interest in reducing inorganic nitrogen in the soil is driving more research on legume and nonlegume intercropping systems. In addition to reducing N input, attention is given to the impact of legumes on nutritive value of forage for livestock production. Research reports on intercropping corn (Zea mays L.) with common bean (Phaseolus vulgaris L.) (Dawo et al., 2009), lablab bean [Lablab purpureus (L.) Sweet] (LB; Armstrong and Albrecht, 2008), or other annual legumes (Carruthers et al., 2000; Armstrong et al., 2008) or intercropping forage sorghum silage [Sorghum bicolor Published in Crop Sci. 51:1307–1313 (2011). doi: 10.2135/cropsci2010.05.0282 Published online 29 Mar. 2011. © Crop Science Society of America | 5585 Guilford Rd., Madison, WI 53711 USA All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.

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Reproduced from Crop Science. Published by Crop Science Society of America. All copyrights reserved.

(L.) Moench] (FS) with annual legumes (Contreras-Govea et al., 2009a) indicate no effect on DM yield compared to the traditional monoculture system, but crude protein (CP) concentration increased in these mixtures. A greater impact of the legume on nutritive value of the mixture was observed when corn and common bean were each planted at a density of 50% of the monoculture crop (Dawo et al., 2007) or when legume had greater plant density than corn (Armstrong and Albrecht, 2008). When the corn–common bean mixtures were ensiled, fermentation parameters such as pH, lactic acid, and total volatile fatty acids were greater in the mixtures than in monoculture corn (Dawo et al., 2007). Legumes are not as easily ensiled as corn silage (CS) or FS. Results from a study by Mustafa and Seguin (2003) indicated that fava bean (Vicia faba L.), pea (Pisum sativum L.), and soybean [Glycine max (L.) Merr.] preserve good nutritive value when ensiled, but buffering capacity and pH were high. When ensiling kura clover (Trifolium ambiguum M. Bieb.) with winter wheat (Triticum aestivum L.), pH was lower for the mixture than the legume, and CP concentration was higher for the mixture than for monoculture winter wheat (Contreras-Govea et al., 2006). Titterton and Maasdorp (1997) ensiled corn with different legumes and with different proportions of soybean forage and reported that legumes must make up at least 40% of the mixture to affect fermentation and nutritive value. They found that quality traits such as pH, CP, ammonia-N, and neutral detergent fiber (NDF) concentration were higher as the proportion of soybean in the mixture increased. Similar results were reported recently by Contreras-Govea et al. (2009c, d), who assessed the fermentation of corn silage in mixture with LB and with other climbing beans. They also reported that, compared to corn alone, CP concentration increased in the mixture, but pH, NDF, and lactic acid concentration also increased, with no significant difference in in vitro digestibility. Anil et al. (2000) conducted a study with sheep to assess the silage quality, feed intake, and in vivo digestibility of corn–sunflower (Helianthus annuus L.), corn–kale (Brassica oleracea L.), and corn–runner bean (Phaseolus coccineus L.) mixtures. They did not find differences in intake between corn alone and corn in mixture. The corn–kale silage mixture had the highest in vivo digestibility, with intermediate values for corn and corn–runner bean mixture. It is clear that mixing legume crops with corn silage should increase CP concentration, but it would also increase other constituents, such as NDF, lactic acid, and total acids concentrations and would potentially decrease digestibility. Therefore, it is important to determine the proper combination of each legume and nonlegume crop that will result in the optimum mixture for nutritive value and fermentation. In addition, little research has been conducted on FS for silage when in mixture with a legume crop. The objective of this study was to assess the nutritive value and fermentation characteristics of CS and FS when in mixture with different proportions of LB for silage. 1308

MATERIAL AND METHODS Field Conditions Corn, FS, and LB were grown at two locations in 2009. Location 1 (Clovis) was New Mexico State University’s Agricultural Science Center at Clovis (34° N, 103°12′ W, and 1348 m elevation), with a mean annual precipitation of 445 mm and Olton clay loam (fine, mixed, superlative, thermic Aridic Paleustoll) soil type. Location 2 (Artesia) was New Mexico State University’s Agricultural Science Center at Artesia (32°45.25′ N, 104°23′ W, and 1026 m elevation), which has a mean annual precipitation of 300 mm and Reagan loam (fine-silty, mixed superactive, thermic Ustic Haplocalcids) soil type. At Clovis, CS (cv. Pioneer 32B34; Pioneer Hi-Bred International, Inc., Johnston, IA), FS (cv. DG712; Dyna Gro Seed, Greeley, CO), and LB [cv. Rio Verde; Smith et al. (2008)] were sown in separate fields on 29 April, 26 May, and 1 June 2009, respectively. At Artesia, FS and LB were the same cultivars used at Clovis, but Mycogen ‘2N804’ (Mycogen, Indianapolis, IN) was used as the CS cultivar. Corn, FS, and LB were sown at Artesia on 12 May, 15 May, and 1 June 2009, respectively. At each location, CS and FS were fertilized according to soil test recommendations. At Clovis, LB seed was not inoculated and was therefore fertilized with 200 kg N ha−1. At Artesia, LB was inoculated with specific Rhizobium strain and therefore did not receive N application. Seeding rate was calculated to achieve a plant density of 79,000 plants ha−1 for CS, 222,000 plants ha−1 for FS, and 148,000 plants ha−1 for LB at each location. At Clovis, CS was harvested at 1/2 milk line starch maturity, FS at late-dough maturity stage of grain, and LB at 20% bloom on 10 Sept. 2009. At Artesia, CS was harvested at 1/3 milk line starch maturity (2 September), FS at soft-dough maturity stage of grain (26 August), and LB at 5 to 10% bloom (1 September and 25 August for mixtures with CS and FS respectively). Trials were irrigated at both locations to prevent water stress during the growing season. There were no severe problems with insects or diseases at either location.

Ensiling Process At Clovis, all three crops and crop mixtures were ensiled on 10 September, while at Artesia, FS and FS–LB mixtures were ensiled on 26 August and CS treatments on 2 September. At both locations, LB was wilted for 18 h before chopping. Crops were chopped separately from random locations within each field. At Clovis, all three crops were chopped to a theoretical particle size of 15 mm with a two row pull-type forage harvester (John Deere, Moline, IL), and at Artesia, all three crops were chopped with a Hege 212 forage plot harvester (Wintersteiger, Inc., Salt Lake City, UT) to a theoretical particle size of 10 mm. After chopping, approximately 20 kg of fresh material were collected in separate plastic buckets for each crop and taken to the laboratory to make mixtures. Twelve handmade mixtures were produced from each location. On a percentage wet weight basis, CS and FS were mixed with LB to obtain the following grass–LB combinations: (i) 100:0, (ii) 90:10, (iii) 75:25, (iv) 50:50, (v) 25:75, and (vi) 0:100. Individual 500 g fresh mixtures were made for each treatment and placed in a 1-L glass jar, with four jars per treatment. For example, for a 50:50 mixture, 250 g of CS or FS and 250 g of LB were weighed in a plastic container and mixed to get a uniform distribution of each

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Statistical Analysis Data analysis was conducted using SAS PROC MIXED software version 9.2 (SAS Institute, 2002) with crop, mixture, and the crop × mixture interaction as fi xed effects and location and the interactions of the fi xed effects with location as random effects. For significant mixtures and mixture by crop interaction effects, orthogonal linear, quadratic, cubic, quartic, and quintic polynomials were used to assess the order of the response trend as well as the nature of the interaction with crop. When significant interactions were detected, orthogonal polynomials were used to assess the degree of trend within each crop. Significance was defi ned at p < 0.05.

CP concentration increased linearly as the amount of LB increased in the mixture. The NDF concentration decreased linearly for both crops as LB increased in the mixture, but CS mixtures declined from 467 g kg−1 at 0% LB to 426 g kg−1 at 100% LB (±12.3 SEM) while FS mixtures declined from 550 g kg−1 at 0% LB to 421 g kg−1 at 100% LB (±12.3 SEM). However, ADF concentration exhibited a cubic trend in CS and a quadratic trend in FS mixtures; despite the significance of higher order terms, in CS–LB mixtures, ADF concentration increased from 272 (±7.0 SEM) to 318 (±7.0 SEM) g kg−1 as LB increased from 0 to 75%, while in FS– LB mixtures, ADF concentration decreased from 348 (±7.0 SEM) to 301 (±7.0 SEM) g kg−1 as LB increased from 0 to 75% (Table 1). The IVTDMD and NDFD concentrations had significant linear and quadratic contrasts but tended to increase with the addition of LB (Table 1), while total digestible nutrients (TDN) decreased linearly. Neutral detergent fiber digestibility was higher in FS mixtures while TDN was higher in CS mixtures.

Ensiled Mixtures Nutritive Value Dry matter concentration in the CS–LB mixtures decreased linearly from 339 (±32.1 SEM) g kg−1 to 257 (±32.1 SEM) g kg−1 as LB proportion increased from 0 to 100%, while no differences were observed among FS–LB mixtures (Table 2). Crude protein concentration of ensiled mixtures had similar trend to pre-ensiled mixtures (Table 1). Crude protein was higher in FS than in CS mixtures. Neutral detergent fiber concentration was similar between crops and among mixtures (p > 0.05; Table 2). In contrast, ADF concentration increased an average of 54 g kg−1 in either CS or FS as the proportion of LB increased from 0 to 75% in the mixture (p < 0.05). The IVTDMD increased linearly only for FS mixtures while NDFD decreased in CS mixtures but increased linearly in FS mixtures (Table 2). In FS mixtures, both IVTDMD and NDFD increased 37 and 79 g kg−1, respectively, as LB proportion increased from 0 to 75% (Table 2). In addition, LB at 100% had greater IVTDMD (834 [±9.8 SEM] g kg−1) and NDFD (573 [±18.8 SEM] g kg−1) than FS at 0% LB. The TDN concentration trend was quadratic both in CS and in FS mixtures (Table 2). In CS mixtures, TDN decreased from 755 (±12.6 SEM) to 684 (±12.6 SEM) g kg−1 as LB increased in the mixture from 0 to 75%, while in FS TDN decreased from 676 (±12.6 SEM) to 631 (±12.6 SEM) g kg−1 as LB increased from 0 to 100%. Ammonia-N increased linearly in both CS and FS as LB proportion increased in the mixture (Table 2).

Fermentation Profile Silage Mixtures

RESULTS Pre-Ensiled Nutritive Value The DM concentration decreased linearly in CS mixtures as the proportion of LB increased at ensiling (Table 1). The CROP SCIENCE, VOL. 51, MAY– JUNE 2011

The pH increased linearly in both CS and FS mixtures as LB make up in the mixture increased (Table 3). Lactic and acetic acids were the dominant acids, while propionic, butyric, and iso-butyric acids were not present or were in undetectable concentrations. Lactic acid was higher in FS

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crop; then the 1-L glass jar (mini-silo) was filled with the mixture. The experimental design was a completely randomized design. There were four replicate jars for each combination of CS–LB and four for each combination of FS–LB (total of 96 jars from both locations). Mini-silos were fermented for 60 d at room temperature (25°C). Average DM density for CS–LB and FS–LB mixtures ranged from 165 to 154 kg m−3, respectively. Before ensiling, two 250-g subsamples for each treatment were placed in a paper bag and oven dried at 60°C for 48 h for DM determination. Subsamples were ground to pass a 1-mm screen in a Wiley Mill (Thomas Scientific, Swedesboro, NJ) and were later analyzed for pre-ensiling chemical composition. At opening, each mini-silo was dumped into an ethanol-disinfected plastic container and mixed to uniformity. A 250-g subsample was placed in a plastic 20 by 30 cm embossed vacuum pouch (Doug Care Equipment, Springville, CA), immediately vacuum sealed using a Fast Vac vacuum machine (Doug Care Equipment, Springville, CA), and frozen to −18°C for later analysis of fiber and fermentation characteristics. The remaining 250 g were also frozen as a backup sample. Crude protein, NDF, acid detergent fiber (ADF), in vitro true dry matter digestibility (IVTDMD), and NDF digestibility (NDFD) were determined using a near-infrared spectroscopy system (NIRS-Foss NIRSystems Model 6500, Eden Prairie, MN) with equation calibrations used for CS and FS (samples were sent to Dairy One Laboratory, Ithaca, NY, for analysis). The pH was measured by weighing 15 g wet sample into 250-mL beaker, adding 200 mL deionized water, stirring, and then measuring using a Thermo Orion 410A meter (Thermo Scientific, Waltham, MA). Volatile fatty acids (acetic, butyric, propionic, and iso-butyric acids) were determined using a Supelco Gas Chromatograph (Sigma-Aldrich, St. Louis, MO) equipped with a 2 m by 2 mm Tightspec ID and 4% carbowax 20M on 80:120 B-DA column. Lactic acid was determined using a YSI 2700 Select Biochemistry Analyzer (YSI Life Sciences, Yellow Springs, OH) by oxidizing L-lactate to hydrogen peroxide and pyruvate. Hydrogen peroxide concentration is directly proportional to L-lactate concentration. Ammonia-N was determined following the procedure for nonprotein nitrogen–urea and ammoniacal nitrogen (AOAC 941.04; AOAC, 2005). All these analyses were conducted at Dairy One Laboratory (Ithaca, NY).

Table 1. Pre-ensiling nutritive value (g kg−1) of corn silage (CS), forage sorghum silage (FS), and lablab bean (LB) in mixture at different proportions. Variable

†

DM CP


NDF ADF IVTDMD NDFD TDN

Crop

0% LB

10% LB

25% LB

50% LB

75% LB

100% LB

Linear

Contrast‡ Quadratic

CS FS CS FS CS FS CS FS CS FS CS FS CS FS

362 290 82 80 467 550 272 348 815 785 600 600 710 670

345 284 88 95 482 534 279 336 805 795 595 620 700 675

334 280 108 118 442 529 260 329 815 810 585 640 705 670

316 272 142 143 435 491 290 304 800 830 550 655 700 665

296 268 153 164 462 467 318 301 840 855 650 690 660 665

277 270 190 199 426 421 307 299 875 880 700 710 665 670

*** *** *** –¶ *** *** –¶ *** *** –¶ *** –¶ ** –¶

NS§ NS NS –¶ NS NS –¶ NS * –¶ * –¶ NS –¶

Cubic NS NS NS –¶ NS NS –¶ * NS –¶ NS –¶ NS –¶

*Significant at the 0.05 probability level. **Significant at the 0.01 probability level. ***Significant at the 0.001 probability level. † DM, dry matter; CP, crude protein; NDF, neutral detergent fiber; ADF, acid detergent fiber; IVTDMD, in vitro true dry matter digestibility; NDFD, neutral detergent fiber digestibility; TDN, total digestible nutrients. ‡ Significance reported for orthogonal polynomial main effect is in row for CS and interaction is in row for FS. No quartic or quintic polynomials were significant. § NS, not significant. ¶ Test not conducted because corresponding main effect or interaction was not significant.

Table 2. Nutritive value characteristics (g kg−1) of corn silage (CS), forage sorghum silage (FS), and lablab bean (LB) in mixture at different proportions. Values are the average of eight jars (mini-silos). Variable† DM CP NDF ADF IVTDMD NDFD TDN NH3 –N#

Crop

0% LB

10% LB

25% LB

50% LB

75% LB

100% LB

Linear

Contrast‡ Quadratic

Cubic

CS FS CS FS CS FS CS FS CS FS CS FS CS FS CS FS

339 259 83 90 396 416 237 268 860 796 646 504 755 676 35 41

327 258 85 100 410 422 251 277 855 800 645 526 753 681 45 53

309 258 106 120 418 420 254 286 846 800 628 526 743 679 54 68

297 252 136 147 401 425 271 306 850 821 625 580 725 690 54 79

277 256 173 172 407 411 301 311 859 833 650 593 684 678 90 91

257 248 202 206 402 396 326 325 829 834 576 573 644 631 100 96

*** *** *** –¶ –¶ –¶ –¶ *** –¶ ** –¶ ** *** *** *** –¶

NS§ NS NS –¶ –¶ –¶ –¶ NS –¶ NS –¶ NS * NS NS –¶

NS NS NS –¶ –¶ –¶ –¶ NS –¶ NS –¶ NS NS NS NS –¶

*Significant at the 0.05 probability level. **Significant at the 0.01 probability level. ***Significant at the 0.001 probability level. † DM, dry matter; CP, crude protein; NDF, neutral detergent fiber; ADF, acid detergent fiber; IVTDMD, in vitro true dry matter digestibility; NDFD, neutral detergent fiber digestibility; TDN, total digestible nutrients; NH3 –N, ammonia N in g per kg of total N. ‡ Significance reported for orthogonal polynomial main effect is in row for CS and interaction is in row for FS. No quartic or quintic polynomials were significant. § NS, not significant. ¶ Test not conducted because corresponding main effect was not significant.

mixtures than in CS and increased linearly with increasing LB. Crop differences were not detected for acetic acid but an increasing linear mixture trend was detected. When assessed within CS and FS, total acid trend was linear and increasing with increasing LB. The lactate:acetate (L:A) ratio decreased linearly with increasing LB (Table 3). 1310

DISCUSSION Nutritive Value The main objective of this study was to assess the fermentation characteristics of CS or FS when LB is added in mixture at different proportions. The DM concentration at the time of ensiling was at the proper level for CS but

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Variable pH Lactic acid Acetic acid Lactate:acetate ratio Total acids

Crop

0% LB

10% LB

25% LB

50% LB

CS FS CS FS CS FS CS FS CS FS

3.79 4.01 43.8 49.4 10.8 12.2 4.1 4.2 54.7 63.3

3.83 4.08 50.7 58.8 13.2 13.2 3.9 4.5 63.9 73.1

3.95 4.21 55.8 66.8 16.5 17.3 3.4 3.8 72.5 84.7

4.10 4.34 66.6 74.7 22.4 22.6 3.0 3.3 89.5 97.9

75% LB 4.31 4.39 76.6 80.3 32.5 30.0 2.4 2.7 109.7 111.0

100% LB 4.58 4.56 81.2 82.4 42.1 40.3 1.9 2.1 120.6 123.4

Linear

Contrast† Quadratic

Cubic

** –§ ** –§ *** –§ *** –§ *** ***

NS‡ –§ NS –§ NS –§ NS –§ NS NS

NS –§ NS –§ NS –§ NS –§ NS *

*Significant at the 0.05 probability level. **Significant at the 0.01 probability level. ***Significant at the 0.001 probability level. † Significance reported for orthogonal polynomial main effect is in row for CS and interaction is in row for FS. No quartic or quintic polynomials were significant. ‡ §

NS, not significant. Test not conducted because corresponding main effect or interaction was not significant.

was below 300 g kg−1 for FS and LB, even though FS was harvested at the maturity stage recommended for ensiling and LB was wilted (Table 1). This has been one of the main issues when ensiling FS. Bolsen (2004) conducted a 25-yr research review for ensiling FS and recommended ensiling at late-dough stage to get the proper DM concentration. He also stated that ensiling at lower DM content tended to lead to a more acetic acid fermentation. On the other hand, although LB was wilted for 18 h before chopping for ensiling, DM concentration also was in a lower range (between 270 and 277 g kg−1) than that recommended (300 g kg−1) for ensiling (McDonald et al., 1991). However, even at these high moisture conditions, all CS–LB and FS–LB silage mixtures fermented well. Previous studies reported similar effects when ensiling soybean (Titterton and Maasdorp, 1997) or LB (Contreras-Govea et al., 2009d) with corn for silage. In those studies, the legumes were not wilted before ensiling and fermentation was stable. Adding LB to CS or FS affected the nutritive value constituents differently. In both CS and FS, CP concentration increased as the proportion of LB increased in the mixture (Table 2). This response is in agreement with previous research (Titterton and Maasdorp, 1997; Dawo et al., 2007; Contreras-Govea et al., 2009c, d). Corn and FS are by nature low in CP. Therefore, adding a legume such as LB, which is high in CP, would be expected to increase CP in the mixture. The effect of LB on CP was similar in both CS and FS. Previous field intercropping studies (Carruthers et al., 2000; Armstrong and Albrecht, 2008) had reported that planting corn and legume at the same time increased CP concentration from 12.9 to 29.0%. However, Dawo et al. (2007) found that a greater increase in CP would be expected when the legume is at 50% of the normal plant density. While we found a linear trend, the increase in CP concentration became noticeable at 25% LB. Crude protein of the 100% LB treatment was lower than those values reported by Mustafa CROP SCIENCE, VOL. 51, MAY– JUNE 2011

and Seguin (2003). Species variation and maturity at harvest could have caused lower CP values in this study. While CP concentration among mixtures was similar between pre-ensiled and ensiled mixtures, it was not the same for NDF concentration. In both CS and FS, the NDF concentration was higher in the pre-ensiled (Table 1) than in the ensiled mixtures (Table 2), which was something unexpected and unusual. Water soluble carbohydrate (WSC) depletion during fermentation would increase the NDF concentration after fermentation. Contreras-Govea et al. (2009c) when mixing corn with different climbing beans reported greater NDF concentration in the fermented than the pre-ensiled treatments. Most of the time, it is assumed that cell wall structural carbohydrates are not affected during fermentation and lactic acid bacteria is consuming the pool of water soluble carbohydrates. Jones et al. (1992) ensiled alfalfa (Medicago sativa L.) at two DM concentrations (290 and 401 g kg−1), with and without inoculants, to assess the effect of fermentation on cell wall structure and reported that low DM concentration and low pH predispose to hydrolysis of cell wall structural carbohydrates. They also found that arabinose and galactose decreased at both DM concentrations, and rhamnose decreased only at the lower DM concentration. All these carbohydrates were part of the hemicellulose fraction, which is included in NDF concentration. Even though they did not find hydrolysis of cellulose, they reported that a previous study also observed some hydrolysis of the cellulosic fraction in alfalfa (Morrison, 1989), which is part of the ADF fraction. Rooke and Hatfield (2003) also reported that ensiling conditions would have an impact on carbohydrates pools. They also mentioned that most of the changes that occurred in the pectic and hemicellulosic fraction could be related to arabinosyl fraction, which is linked to xylose and galactose. These structural carbohydrates are more susceptible to acid hydrolysis even under weak acid conditions (Rooke and Hatfield, 2003). In our study, silage conditions were adequate for the cell wall hydrolysis reported by Jones et

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Table 3. Fermentation characteristics (g kg−1) of corn silage (CS), forage sorghum silage (FS), and lablab bean (LB) in mixture at different proportions. Values are the average of eight jars (mini-silos).


al. (1992). First, DM concentration of pre-ensiling mixtures was below 350 g kg−1 for CS–LB mixtures and below 300 g kg−1 for FS–LB mixtures. Second, the pH across CS and FS mixtures ranged from 3.79 to 4.58, which were below those reported by Jones et al. (1992), and third, lactic acid concentration increased as the amount of LB was added to the mixture. Therefore, it is likely that acidic conditions were conducive to cell wall hydrolysis, which decreased NDF concentration and in some degree also ADF concentration of either CS or FS mixtures. If this happened, an impact on the pool of WSC would be expected. Unfortunately, WSC was not measured. Apparently, ADF fraction was also susceptible to hydrolysis, but at a lower grade than NDF fraction. The ADF concentration of ensiled mixtures with greater proportion of CS and FS, such as 90:10 CS:LB and 90:10 FS:LB, was lower (Table 2) than pre-ensiled conditions (Table 1). Even with this hydrolysis effect, it was observed that ADF concentration increased as the amount of LB increased in the mixture (Table 2). These results are in agreement with those reported by Titterton and Maasdorp (1997) and Contreras-Govea et al. (2009c, d), assessing corn–legume mixtures, and by Lima et al. (2010), assessing sorghum–soybean mixture, in which ADF concentration increased with the addition of legume to corn or sorghum. The NDFD followed opposite patterns between CS and FS (Table 2). In CS–LB mixtures, NDFD decreased as the proportion of LB increased in the mixture from 0 to 50%, while the opposite was observed in FS–LB mixtures. These results can be explained by the NDFD of 100% LB. The 100:0 CS:LB mixture had greater NDFD than the 0:100 CS:LB mixture (Table 2), while the 100:0 FS:LB mixture had lower IVTDMD and NDFD than the 0:100 FS:LB mixture (Table 2); therefore, adding LB to CS decreased NDFD, while adding LB to FS increased IVTDMD and NDFD (Table 2). These results were in agreement with those reported by Titterton and Maasdorp (1997) and Contreras-Govea et al. (2009c, d) in which NDFD declined by adding beans to corn although they also detected declining IVTDMD. In addition, our IVTDMD values were similar in magnitude to those reported by Contreras-Govea et al. (2009c, d), but greater than those reported by Titterton and Massdorp (1997). Titterton and Massdorp (1997) reported IVTDMD values that were determined using a different technique. Bolsen (2004) reported that variability among FS cultivars in nutritive value is greater than grain sorghum cultivars. Therefore, it is speculated that the positive impact of adding LB in mixture with FS could be greater in low-quality FS than in high-quality FS cultivars. Total digestible nutrient is a calculated value to estimate the energy value of a feed (National Research Council, 2001). A summative approach that considers the true digestibility of CP, NDF, nonfiber carbohydrates, and fatty acids is used to determine TDN concentration (National Research Council, 2001). The TDN was the only ensiled variable that showed a quadratic trend (Table 2). In CS–LB 1312

mixtures, TDN decreased as the proportion of LB increased from 0 to 100%, while in FS–LB mixtures, TDN increased when LB increased from 0 to 50% but then declined when LB increased from 50 to 100% (Table 2). It is important to note that high IVTDMD was not parallel to TDN. While the IVTDMD ranged from 796 to 860 g kg−1 across CS–LB and FS–LB mixtures, the TDN ranged from 630 to 755 g kg−1 (Table 2), with greater values in CS–LB than FS–LB mixtures (Table 2). Legumes such as LB and alfalfa (TDN = 564 g kg−1; National Research Council, 2001) tend to have low TDN and high digestibility. Contreras-Govea et al. (2009b) reported average in vitro true digestibility of 822 g kg−1 in alfalfa silage. In addition, corn silage is well known as a high energy crop with a TDN of 688 g kg−1 (National Research Council, 2001), while TDN of forage sorghum (TDN = 567 g kg−1; National Research Council, 2001) is less than corn. Ammonia-N increased as the proportion of LB increased in the mixture in either CS or FS. These results were expected because legumes have high CP concentration, which is conducive to greater proteolysis than CS or FS. In addition, legumes have greater buffering capacity than grasses (Buxton and O’Kiely, 2003). As a consequence, higher ammonia-N formation should be expected in the mixture as the proportion of legumes increases (McDonald et al., 1991). Other studies also reported lower energy and higher ammonia in corn–legume or sorghum–legume mixtures than corn- or sorghum-only silage (Titterton and Maasdorp, 1997; Contreras-Govea et al., 2009c; Lima et al., 2010).

Fermentation Characteristics It is well documented that legume silages such as alfalfa, fava bean, soybean, pea, red clover (Trifolium pratense L.), and kura clover have pH that range from 4.0 to 4.8 and high lactic (>50 g kg−1 DM) and acetic (20 g kg−1 DM) acid concentrations and ammonia-N concentration (Owens et al., 1999; Mustafa and Seguin, 2003; Contreras-Govea et al., 2006) as a result of high buffering capacity and extended fermentation. In our findings, pH and lactic, acetic, and total acid concentrations increased as the proportion of LB increased in the mixture in either CS or FS mixtures (Table 3). These results were in agreement with those reported previously by other studies (Titterton and Maasdorp 1997; Contreras-Govea et al., 2009c; Lima et al., 2010). It was consistent in either CS or FS that increasing the amount of LB and decreasing CS or FS in the mixture led to an extended fermentation, which increased fermentation end products. It was suggested that a 3:1 L:A ratio is a good indicator of homolactic fermentation (McDonald et al., 1991). Given this, it was assumed that the lower the L:A ratio, the more heterolactic was the fermentation. In our results, L:A ratio decreased as LB increased in the mixture. This could have positive and negative aspects. The positive aspect is that corn silage has low aerobic stability (Kleinschmit and

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CONCLUSION The ensiling studies that simulated intercropping of annual legumes with CS or FS have demonstrated that CP concentration can be increased in these mixtures. Our data showed that LB can be ensiled with CS or FS and produce acceptable fermentation in all mixtures. However, a greater benefit in nutritive value was observed in FS than CS when LB was between 25 and 75% of the mixture. In addition, increasing CP concentration in the silage could potentially reduce CP supplementation to cattle and possibly reduce N excretion to the environment. This is an issue that requires more research. Acknowledgments The authors thank Aaron Scott, Umesh Rangappa, Maria Teresa Nunez, Servando Bustillos, and Ruben Pacheco for their technical support and Dr. Hector Gonzalez and Aracely Orozco from the University of Ciudad Juárez, Mexico, for their support during the ensiling process. Salaries and research support were provided by state and federal funds appropriated to the New Mexico Agricultural Experiment Station. This research was also partially supported by USDA-National Research Initiative, Grant Number 2007-35102-18120.

References Anil, L., J. Park, and R.H. Phipps. 2000. The potential of forage-maize intercrops in ruminant nutrition. Anim. Feed Sci. Technol. 86:157–164. AOAC. 2005. Official methods of analysis of the AOAC International. 18th edition. AOAC Intl., Gaithersburg, MD. Armstrong, K.L., and K.A. Albrecht. 2008. Effect of plant density on forage yield and quality of intercropped corn and lablab bean. Crop Sci. 48:814–822. Armstrong, K.L., K.A. Albrecht, J.G. Lauer, and H. Riday. 2008. Intercropping corn with lablab bean, velvet bean, and scarlet runner bean for forage. Crop Sci. 48:371–379. Bolsen, K.K. 2004. Sorghum silage: A summary of 25 years of research at Kansas State University. In J.W. Smith (ed.) Southeast Dairy Herd Management Conference Proceedings, Macon, GA. 16–17 Nov. 2004. Rhodes Center for Animal and Dairy Sci., University of Georgia, Athens, GA. Buxton, D.R., and P. O’Kiely. 2003. Preharvest plant factors affecting ensiling. p. 199–250. In D.R. Buxton et al. (ed.) Silage science and technology. ASA, CSSA, and SSSA, Madison, WI. Carruthers, K., B. Prithiviraj, Q. Fe, D. Cloutier, R.C. Martin, and D.L. Smith. 2000. Intercropping of corn with soybean, lupin and forages: Silage yield and quality. J. Agron. Crop Sci. 185:177–185. CROP SCIENCE, VOL. 51, MAY– JUNE 2011

Contreras-Govea, F.E., K.A. Albrecht, and R.E. Muck. 2006. Spring yield and silage characteristics of kura clover, winter wheat, and in mixtures. Agron. J. 98:781–787. Contreras-Govea, F.E., L.M. Lauriault, M. Marsalis, S. Angadi, and N. Puppala. 2009a. Performance of forage sorghumlegume mixtures in southern High Plains, USA. Forage and Grazinglands doi:10.1094/FG-2009-0401-01-RS. Contreras-Govea, F.E., R.E. Muck, and K.A. Albrecht. 2009b. Yield, nutritive value and silage fermentation of kura clover-reed canarygrass and lucerne herbages. Grass Forage Sci. 64:374–383. Contreras-Govea, F.E., R.E. Muck, K.L. Armstrong, and K.A. Albrecht. 2009c. Nutritive value of corn silage in mixture with climbing beans. Anim. Feed Sci. Technol. 150:1–8. Contreras-Govea, F.E., R.E. Muck, K.L. Armstrong, and K.A. Albrecht. 2009d. Fermentability of corn–lablab bean mixtures from different planting densities. Anim. Feed Sci. Technol. 149:298–306. Dawo, M.I., J.M. Wilkinson, and D.J. Pilbeam. 2009. Interactions between plants in intercropped maize and common bean. J. Sci. Food Agric. 89:41–48. Dawo, M.I., J.M. Wilkinson, F.E.T. Sanders, and D.J. Pilbeam. 2007. The yield and quality of fresh and ensiled plant material from intercropped maize (Zea mays) and beans (Phaseolus vulgaris). J. Sci. Food Agric. 87:1391–1399. Jones, B.A., R.D. Hatfield, and R.E. Muck. 1992. Effect of fermentation and bacterial inoculation on lucerne cell walls. J. Sci. Food Agric. 60:147–153. Kleinschmit, D.H., and L. Kung, Jr. 2006. A meta-analysis of the effect of Lactobacillus buchneri on the fermentation and aerobic stability of corn and grass and small-grain silages. J. Dairy Sci. 89:4005–4013. Lima, R., M. Lourenco, R.F. Diaz, A. Castro, and V. Fievez. 2010. Effect of combined ensiling of sorghum and soybean with and without molasses and lactobacilli on silage quality and in vitro rumen fermentation. Anim. Feed Sci. Technol. 155:122–131. McDonald, P., A.R. Henderson, and S.J.E. Heron. 1991. The biochemistry of silage. 2nd ed. Chalcombe Publ., Bucks, UK. Morrison, I.M. 1989. Influence of some chemical and biological additives on the fibre fraction of lucerne on ensilage in laboratory silos. J. Agric. Sci. 111:35–39. Mustafa, A.F., and P. Seguin. 2003. Characteristics and in situ degradability of whole crop faba bean, pea, and soybean silages. Can. J. Anim. Sci. 83:793–799. National Research Council. 2001. Nutrient requirements of dairy cattle, 7th rev. ed. Natl. Acad. Sci., Washington, D.C. Owens, V.N., K.A. Albrecht, R.E. Muck, and S.H. Duke. 1999. Protein degradation and fermentation characteristics of red clover and alfalfa silage harvested with varying levels of total nonstructural carbohydrates. Crop Sci. 39:1873–1880. Rooke, J.A., and R.D. Hatfield. 2003. Biochemistry of ensiling. p. 95–139. In D.R. Buxton et al. (ed.) Silage science and technology. ASA, CSSA, and SSSA, Madison, WI. SAS Institute. 2002. User’s guide: Statistics, version 9.2 ed. SAS Inc., Cary, NC. Smith, G.R., F.M. Rouquette, Jr., and I.J. Pemberton. 2008. Registration of ‘Rio Verde’. Lablab. J. Plant Reg. 2:15. Titterton, M., and B.V. Maasdorp. 1997. Nutritional improvement of maize silage for dairying mixed crop silages from sole and intercropped legumes and a long season variety of maize. 2. Ensiling. Anim. Feed Sci. Technol. 69:263–270. Weiss, W.P., D.G. Chamberlain, and C.W. Hunt. 2003. Feeding silage. p. 469–504. In D.R. Buxton et al. (ed.) Silage science and technology. ASA, CSSA, and SSSA, Madison, WI.

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Kung, 2006); therefore, adding LB would increase acetic acid concentration, which could result in better aerobic stability of CS–LB mixtures. The negative aspect is that FS is normally high in acetic acid (Bolsen, 2004). Adding LB to FS would potentially increase acetic acid concentration to a level (>40 g kg−1 DM) that could affect palatability and dry matter intake (Weiss et al., 2003). Another possibility for mixing FS with LB could be harvesting LB at a later maturity stage, increasing DM concentration of the mixture and potentially producing a lower amount of acetic acid.