Published online 3 January 2006
Published in Agron J 98:1-7 (2006)
DOI: 10.2134/agronj2004.0134
© 2006 American Society of Agronomy
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Production Papers
The Effect of a Baler Chopping System on Fermentation and Losses of Wrapped Big Bales of Alfalfa
Giorgio Borreani* and
Ernesto Tabacco
Dipartimento di Agronomia, Selvicoltura e Gestione del Territorio, Univ. of Turin, via Leonardo da Vinci, 44, 10095 Grugliasco (TO), Italy
* Corresponding author (giorgio.borreani{at}unito.it)
Received for publication May 19, 2004.
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ABSTRACT
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The improvement of wrapped big bale silage quality by increasing bale densities should be an important target. The objectives of this research were to evaluate the effects of the use of a cutting system (15 knives spaced 93 mm apart) installed behind the windrow pickup of a fixed chamber round baler. Three field trials were conducted near Turin, Italy (44°50' N, 7°40' E) by ensiling wrapped round bale of first- and second-cutting alfalfa (Medicago sativa L.) at different dry matter (DM) concentrations. The DM and crude protein (CP) losses at baling, forage mean particle length, wet and dry bale weights, bale density, fermentation pattern, and the conservation losses were evaluated. The DM losses at baling ranged from 0.5 to 2.0% and from 0.7 to 4.7% of DM yield at cutting for unchopped and chopped treatments, respectively. The chopping system increased the percentage of stems shorter than 10 cm from 14 to 38% on a DM basis. Chopping increased DM bale density by about 4% in all the trials. After 140 d of conservation the final fermentation quality of silages was not consistently improved by chopping.
Abbreviations: ANOVA, analysis of variance • C, baled with chopping device • CP, crude protein • DM, dry matter • DM35, high-moisture silage • DM50, low-moisture silage • L/S, leaf to stem ratio • MSW, mean stage by weight • NDF, neutral detergent fiber • TN, total nitrogen • UC, baled without the chopping device • WSC, water-soluble carbohydrates
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INTRODUCTION
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ALFALFA, conserved as silage or hay, could represent the most reliable source of forage of high nutritive value and make a significant contribution to the whole farm economy (Colombari et al., 2001; Albrecht and Beauchemin, 2003). The rise of baled silage over the last 15 yr in Europe has led to a remarkable increase in the amount of herbage stored as silage, which ranges between 30 and 80% of the total harvested dry matter, depending on which countries are considered (Wilkinson and Toivonen, 2003). Big bale silage, which is a flexible and economical system, has become popular as an option for storing excellent quality forage and can provide the opportunity of maintaining the high feeding value of the young alfalfa herbage (Lingvall, 1995). The making of big bale silage involves many mechanical treatments ranging from harvesting to storage to achieve high quality forage in terms of nutritive value and hygienic characteristics. The intense activity of manufacturers has led to a great improvement in some harvesting phases of the ensiling process such as mower-conditioners that cut and spread the forage in a thin layer in one operation (Bosma, 1995), combined baler-wrapper machines (Münster, 2001), and plastic films with low air permeability (Wilkinson and Rimini, 2002; Borreani and Tabacco, 2005). Alfalfa baleage, compared with other harvesting systems, has a greater flexibility with regard to the harvesting date, is less weather dependent, and has greater flexibility in ration formulation. The technique of big-bale silage is, however, particularly prone to spoilage, because of the high surface area/volume ratio of the bale, the ease with which the cover can be damaged, and the lower packing density of the ensiled herbage (O'Kiely et al., 2002). As anaerobiosis is the most critical requirement of ensilage, the effects of the plastic film, bale density, and forage DM concentration present particular risks to quantitative and qualitative conservation losses (Woolford, 1990). As the herbage is not chopped the release of the nutrients that are necessary for lactic acid fermentation is restricted (Jonsson et al., 1990). Moreover, the crimped herbage is rolled, which does not give the bale a high density and it makes oxygen exclusion more difficult. Silage compaction could be improved by reducing the chop-length of herbage, with denser bales resulting in lower costs of handling and transport (Ohlsson, 1998a).
Round balers with a cutting system behind the pickup are available on the market and these could provide an improvement in the density of silage. The technique of cutting the herbage into shorter lengths on entry to the bale chamber could facilitate the release of plant sugars, provide an aid to better bale density, and make it easier to feed cows by total mixed ration (Shinners, 2003).
The aim of this work was to evaluate the effects of a baler cutting system on fermentation quality, DM losses, and densities of big bale silage of alfalfa.
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MATERIALS AND METHODS
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The research was conducted on a dairy farm at None (TO) near Turin, Italy (44°50' N lat, 7°40' E long) in 1998. Three trials (two in the first cut and one in the second) were performed in two producing alfalfa fields of 3.0 and 2.5 ha, respectively. The trials therefore offered a wide range of drying conditions in terms of weather, yield, initial moisture concentration, and stage of maturity (Table 1). Temperature, rainfall, and Class A evaporation pan data were collected from a weather station located 200 m from the field. All the forages, mown at a stubble height of 4 cm and conditioned, were spread on the whole field surface within 2 h. A fixed chamber round baler with a cutting system (15 knives spaced 93 mm apart) (New Holland, 5930-crop cutter, PA) was used to make wrapped big bales (1.2 m diam. by 1.2 m width). The crop precutter device consists of a rotor with a gang of paired teeth placed in a helical pattern. This rotor is placed between the pick-up and bale chamber so the crop is cut before bale formation (fully described by Shinners, 2003 in Fig. 8–13, p. 393–394).
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Table 1. Harvest dates, main characteristics of alfalfa herbage at cutting, dry matter (DM) concentration at ensiling, and wilting time of the three ensiling trials conducted at Turin (Italy).
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Different DM concentrations were obtained for the silages by allowing the forage to wilt in the field over different time between the trials. Alfalfa was raked before baling when expected DM concentrations were reached. In Trial I, two different wilting levels (350 and 500 g DM kg–1) were compared and they will be referred to in the text as DM35, and DM50, respectively. For all three trials the forages were harvested from alternate windrows: half baled with the chopping device on (C), and half without the chopping system (UC). Forage DM concentration in the field was determined with a microwave oven to assess the planned level for baling (Farmer and Brusewitz, 1980). The baler pressure was adjusted according to the manufactor's recommendations for forage DM. Round bales were wrapped individually within 3 h after baling using a stretch film (four 0.5 m wide by 25 µm thick layers) with 50% overlap between two successive strips of film. An average of four round bales were harvested for each treatment.
In Trial III, the mean particle length of the forage was determined on samples of chopped and unchopped herbages taken from inside the baler chamber. The mean particle length of the forage was determined by dividing by hand the herbage sample into four classes (0–5 cm; 5–10, 10–20 cm; >20 cm). The DM chamber losses at baling were determined for each bale by harvesting all the material loss collected with a sheet attached beneath the baler chamber. Ejection loss material was carefully raked and weighed when each bale was dropped. Samples were taken for DM measurement for each weighing. The DM losses at baling per hectare was calculated by referring the DM chamber losses determined for each bale to the harvested area (length of the harvested windrow per bale x raking width). The DM losses over the conservation period were evaluated by weighing the bales before wrapping and before being fed to the animals. Bales were safely stored on their end outside on the ground and covered by a 200-µm white plastic film for 140 d before final sampling. Two bales were sampled for each treatment at five different moments during storage to evaluate fermentation patterns. Sampling was performed by coring the bale from its side to a depth of about 450 mm with a corer (50 mm diam.). The coreholes were plugged with a 550 mm long and 60 mm diameter wood stick. The wood stick was left about 50 mm outside the bale and it was immediately sealed together with the plastic film using silicone rubber, to avoid air damage and molding. The subsequent sample was performed 0.5 m apart from the preceding sample. One sample per bale was done at each sampling time.
Analytical Procedures
Herbage samples were taken at cutting and before ensiling to determine the DM concentration at 90°C in a forced-draft oven until constant weight and the morphological stage, following the mean stage by weight (MSW) method proposed by Kalu and Fick (1981). Herbage subsample of about 50 stems was divided by hand into leaf components (leaflets and petioles) and stem components (stems, stipules, and floral parts when present) and dried at 90°C in a forced-draft oven until constant weight to determine the leaf/stem ratio (L/S). Samples were dried for analyses of forage nutritive value by oven-drying to constant weight at 60°C, air equilibrated, weighed, and ground in a Cyclotec mill (Tecator, Herndon, VA) to pass a 1-mm screen. The dried samples were analyzed for total N (TN) by combustion (Macro-N, Foss Heraeus Analysensysteme, Hanau, Germany), crude protein (TN x 6.25), and neutral detergent fiber (NDF) as described by Robertson and Van Soest (1981). Water-soluble carbohydrates (WSC, according to Deriaz, 1961) were determined in water extracts of frozen samples (–20°C). Silage samples collected during the trials were subsampled and immediately analyzed for DM concentration by oven-drying at 80°C for 24 h and for TN. Wet samples stored at –20°C were homogenized and extracted for 4 min in a Stomacher blender (Model 400, Seward Ltd, London, UK) in water or in H2SO4 0.05 M. The pH was determined in the water extracts. Ammonia nitrogen (NH3–N), determined using a specific electrode, was quantified in the acid extract. The lactic and monocarboxylic acids (acetic, butyric, propionic acids) were determined by high performance liquid chromatography (Canale et al., 1984).
Statistical Analysis
In each trial two treatments (chopped and unchopped forage) were compared with four bales as replicates. The DM losses, bale weights, and chemical compositional data were analyzed for their statistical significance via an analysis of variance, with their significance reported at a 0.05 probability level, using the ANOVA COMMAND of the Statistical Package for Social Science (v 11.5, SPSS, Chicago, IL). The fermentation losses were analyzed by performing the analysis of variance on the values of the differences between the weight at baling and the weight at the end of conservation. The forage particle classes, expressed as DM percentage of the sample, were analyzed by performing ANOVA on angular transformed values (arcsine transformation). Data were analyzed separately by trial because of the different DM content reached at baling that greatly influenced mechanical losses and fermentation patterns. Significant differences between means were identified by the P values of analysis of variance and effects were considered significant at P < 0.05.
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RESULTS AND DISCUSSION
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Crops with different stages of development were chosen to be representative of different drying conditions, initial moisture concentrations, and fiber concentrations. The main nutritive characteristics of the herbage at cutting and wilted before ensiling are reported in Table 1. The DM yield can be considered typical of a first cut (Trials I and II) and of a second cut (Trial III) of alfalfa in the Po plain (Borreani et al., 2000). The herbage in Trial I was characterized by good nutritive value, in terms of NDF and CP (high L/S), and a relatively low DM concentration at cutting due to its early stage of cutting (low MSW). Trial II was performed on a more advanced stage crop with a lower quality. The third trial was made in the early stage of second cut with MSW < 3 (early bud) and L/S = 0.50. The WSC concentrations at cutting were relatively constant during the trials, and varied from 36 to 40 g kg–1 DM. The DM concentrations reached by wilting were 350 and 490 g kg–1 in Trial I, 605 g kg–1 in Trial II, and 380 g kg–1 in Trial III.
The weather conditions during the field wilting are shown in Table 2. The favorable drying conditions of Trials I and III with more than 11 h of sunshine and a pan evaporation of around 6 mm d–1, allowed the alfalfa to be harvested the same day as mowing or, for the DM50 treatment in Trial I, in the following day (see Table 1). In Trial II the 3 d following mowing were overcast and 36.4 mm of rainfall occurred, delaying harvesting for 4 d.
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Table 2. Weather conditions recorded during wilting experiments in the first (Trial I and II) and second (Trial III) alfalfa cuts at Turin (Italy).
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The DM losses at baling for the UC treatment ranged from 26.8 to 110.4 kg DM ha–1, which were equivalent to 0.5 to 2.0% of the DM yield at cutting (Table 3). When the chopping system was on, the DM losses at baling ranged from 53.2 to 253.0 kg DM ha–1, corresponding with 0.7 to 4.7% of DM yield at cutting. The values observed were comparable with DM losses reported by Collins et al. (1987) for alfalfa hay harvested in good conditions and they correspond to the lower estimates of DM losses when alfalfa is baled with large round balers (Macdonald and Clark, 1987). The data in Table 3 show that the amount of DM losses was directly proportional to the DM concentration of the forage at baling, and was doubled when the chopping system was on.
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Table 3. Silage dry matter (DM) losses at baling with chopped and unchopped bales of first (Trial I and II) and second (Trial III) alfalfa cuts (Turin, Italy).
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The chopping system increased the percentage of stems that were shorter than 10 cm from 14 to 38% on DM basis (Table 4). This reduction in particle size may reduce the power requirements and loading time during feed mixer operations (Bisaglia et al., 2002). Other advantages are that the dispersion of additives within the bale is likely to be improved in bales made from precut forage (Lingvall, 1995).
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Table 4. Fraction of total sample in each of four forage particle length classes in chopped and unchopped round bale alfalfa herbage (Trial III, second cut) conducted at Turin (Italy).
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The DM weight of the bales ranged from 221 to 265 kg bale–1 for the UC treatment, and from 227 to 277 kg bale–1 for the C treatment, whereas the DM density of the bales ranged from 163 to 196 kg m–3 and from 167 to 204 kg m–3 for the UC and C treatments, respectively (Table 5). The UC values are similar to other round bale silage densities reported in the range of 150 to 190 kg DM m–3 (Tremblay et al., 1997), while the C values are consistent with the results of Han et al. (2004), who reported bale densities ranging from 167 to 207 kg DM m–3. The DM bale density increases due to the chopping system ranged from 2.5 to 4.7%. Similar values of about 3% were found in the same environment on alfalfa baled at 431 g DM kg–1 using a big baler with a variable chamber (Borreani and Tabacco, 2002), while differences of around 8.4% were found on a permanent meadow with DM concentration of 473 g DM kg–1 (Borreani and Tabacco, unpublished data, 1999). Increases in weight of big bales due to the chopping device have been reported by other researchers (Tremblay et al., 1997; Ohlsson, 1998b; Bisaglia et al., 2002). Bisaglia et al. (2001) found differences of 7.8 and 14.3% on alfalfa baled at 507 g DM kg–1, for fixed-chamber and variable-chamber balers, respectively, while they found differences of 3.3 and 8.7% on Italian ryegrass (Lolium multiflorum Lam.) (336 g DM kg–1) for fixed-chamber and variable-chamber balers, respectively. Ohlsson (1998b) found values from 7 to 9% on whole crop barley (Hordeum vulgare L.) with a variable-chamber baler. All these values are slightly greater than those observed in the trials presented here. However, the trials that were performed in Sweden and Norway on round bales at DM concentration of 300 g DM kg–1 showed that precutting does not result in any change in bale densities (Lingvall, 1995).
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Table 5. Physical characteristics of chopped and unchopped round bales of first (Trial I and II) and second (Trial III) alfalfa cuts (Turin, Italy).
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After 140 d of conservation all the silages were well fermented, with low levels of ammonia-N and butyric acid (Table 6). Lactic acid, acetic acid, and pH, were in the expected ranges for alfalfa bale silage. Comparison between wrapped round bale silage (which has long forage particles) and other silo types have consistently shown reduced fermentation and higher pH in the bale silages (Muck et al., 2003). The chopping system did not affect the final quality of silages, except for the lactic acid, propionic acid, butyric acid, and ammonia-N in Trial I (DM35). This was probably due to the slightly lower DM concentration at baling in treatment C. Increasing the DM concentration of round bales by wilting had an inhibitory role on silage fermentation due to a restriction of the microflora activity, as indicated by the pH and lower concentration of lactic and acetic acids (Muck, 1990). The ammonia-N never exceeded 100 g kg–1 TN, a value which has traditionally been taken as an indicator of good quality fermentation (Pahlow et al., 2003). The weight losses were greater in the UC than in the C treatment, although they were always lower than 3.1% on DM and differences between treatments were not always significant (P > 0.05).
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Table 6. Fermentation products and weight losses of 140 d silages of first (Trial I and II) and second (Trial III) alfalfa cuts (Turin, Italy).
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The changes in pH (Fig. 1
), lactic acid (Fig. 2
), and ammonia-N (Fig. 3
) during conservation confirmed that there was no consistent effect of the chopping system on fermentation patterns of silages. The reduction in particle size due to the chopping device is probably not sufficient to enhance the release of plant nutrients that support the growth of acid-producing bacteria, as occurs in precision chopped silage. In Trial I (DM35) and in Trial III, which were characterized by DM concentration ranging from 365 to 381 g kg–1, the pH dropped to values of around 5.0 within 50 d of fermentation and then remained almost constant, while in higher DM concentration silages (DM50 of Trial I and Trial II) the pH remained practically constant during the entire conservation period. The lactic acid concentration reflects the observed pH patterns in all the trials as reported in literature for bale silage (McDonald et al., 1991). In low DM concentration silage, the fast drop in pH and the prevalent lactic acid fermentation prevent the production of large amounts of ammonia (Fig. 3), whereas in high DM concentration silages the water concentration prevents ammonia release due to microbial activity (Pahlow et al., 2003).
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Fig. 1. Changes in pH during fermentation of alfalfa-wrapped bale silage of first and second cuts harvested and ensiled at Turin (Italy). Within date of sampling, NS and * indicate not significant and sig-nificant difference at P < 0.05, respectively.
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Fig. 2. Changes in lactic acid during fermentation of alfalfa-wrapped bale silage of first and second alfalfa cuts harvested and ensiled at Turin (Italy). Within date of sampling, NS and * indicate not significant and significant difference at P < 0.05, respectively.
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Fig. 3. Changes in ammonia-N during fermentation of alfalfa-wrapped bale silage of first and second alfalfa cuts harvested and ensiled at Turin (Italy). Within date of sampling, NS and * indicate not significant and significant difference at P < 0.05, respectively.
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The CP concentration of chopped and unchopped bales, measured immediately after baling, are reported in Table 7. No differences were found between the chopped and unchopped bales. The alfalfa losses showed an average CP concentrations of 239 g kg–1 DM in Trial I and III, and of 196 g kg–1 DM in Trial II. These values are consistent with those found (242 g CP kg–1 DM) by Rotz and Abrams (1988) for the quality of baler chamber losses during alfalfa harvesting. These losses caused a reduction in the CP concentrations of the harvested forage. The overall CP losses from cutting to harvesting ranged from 7.4 to 18.8% of the CP concentration of herbage at cutting.
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Table 7. Crude protein concentrations and losses of chopped and unchopped bales of first (Trial I and II) and second (Trial III) alfalfa cuts (Turin, Italy).
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CONCLUSIONS
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Many new balers are including a precutter as optional equipment. One reason often given for adopting this technology is the increased bale density and improved silage fermentation that results. In the three trials, chopping device increased DM bale density by about 4% but results were not consistent across the trials especially with low-moisture alfalfa silage. Even though chopping doubled the percentage of stems shorter than 20 cm, it has been concluded that forage balers equipped with the cutting device could not improve the fermentation quality of alfalfa silage.
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ACKNOWLEDGMENTS
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The authors thank Renato Delmastro and Gianni Perin (Istituto per la Meccanizzazione Agricola–CNR Turin, Italy) for the technical assistance and the setting up of the balers. The balers were kindly supplied by New Holland–FIATAGRI, Italy. This work was funded by the Ministero delle Politiche Agricole e Forestali (MiPAF) Project "Gestione delle risorse prato-pascolive alpine." The authors contributed equally to the work described in this paper. Mention of trade names is for the benefit of the reader and does not constitute endorsement by the University of Turin, Italy over other products not mentioned.
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Agron. J.,
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TOP
ABSTRACT
INTRODUCTION
