An ASABE Meeting Presentation Paper Number: 096672
Characteristics and compositional variation in round and square sorghum bales under
different storage conditions Amit Khanchi, Graduate Research Assistant Biosystems and Agricultural Engineering, Oklahoma State University, Stillwater, OK 74078, Email: [email protected]
Carol L. Jones, Assistant Professor Biosystems and Agricultural Engineering, Oklahoma State University, Stillwater, OK 74078, Email: [email protected]
Bhavna Sharma, Graduate Research Assistant Biosystems and Agricultural Engineering, Oklahoma State University, Stillwater, OK 74078, Email: [email protected]
Written for presentation at the 2009 ASABE Annual International Meeting Sponsored by ASABE Grand Sierra Resort and Casino Reno, Nevada June 21 – June 24, 2009 Abstract: The dry matter loss during storage of biomass is one of the crucial factors that effect the final yield of ethanol. This study evaluated the dry matter loss and changes in chemical composition of round and square sorghum bales under various storage conditions. Forage sorghum was harvested and field dried to a moisture content of approximately 11 %. The biomass was packaged in square and round bales and subjected to different storage treatments: inside and outside. The outside treatment included storage of bales on pallets covered with tarps, and storage on pallets and on the ground without tarps. After six months in storage, samples from each bale were analyzed for variation in chemical constituents, dry matter, and moisture content. Square bales stored outside on the ground lost the maximum amount (12.6 %) of dry matter, and round bales stored inside lost the minimum amount (4.67 %). There was a significant increase in ADL and ADF content of stored sorghum samples. No significant change was observed for mineral and cellulose content. Keywords: Sorghum, forage, storage, dry matter loss, chemical constituent
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Introduction Recently there has been an increasing demand for inexpensive and new feedstocks for bioethanol production. According to Balat and Balat (2009) bio ethanol feed stocks can be divided into three major groups: sucrose containing feed stocks, starchy feed stocks, and lignocellulosic biomass. The major disadvantages of using sucrose and starch containing feed stocks are that they are expensive and are often required in other applications. Therefore, there is a need for alternative feedstocks to meet the increasing demand of ethanol. Sorghum is one of the most promising crops, which can be used as biomass energy feed stock. Coble and Egg (1987) investigated dry matter loss during hay production and storage of sweet sorghum for a period of five and a half months and reported that storage losses were 10.1 % and 18.1 % for indoor and outdoor storage, respectively. Several storage studies (Cundiff and Marsh, 1996; Monti et al., 2009; Sanderson et al., 1997; Wiselogel et al., 1996) conducted on various forage materials suggest that most deterioration occurs in the outer layers of round and square bales. The studies suggested that storage techniques which minimize the deteriorating environmental factors and allow better drainage pattern of water will minimize the dry matter losses from the bales. For a large scale biofuel production facility, it is important to have a continuous supply of feedstock to the biorefinery. Thus to ensure a continuous availability of biomass, storage becomes a vital factor (Wiselogel et al., 1996). The main concerns in a biomass storage system are the cost of storage and the dry matter losses during the storage period. For biofuel production, indoor storage of bales will affect the overall economics of the biofuels production process as the cost of storing bales will be higher. Outside unprotected storage results in greater dry matter losses, changes in composition, and loss of both structural and nonstructural components (Wiselogel et al., 1996). The spoilage of bales during storage is mainly due to the biochemical reactions of respiration by microbes. It involves the conversion of carbohydrates and oxygen into carbon dioxide, water, and heat, which results in raising the bale temperature and loss in dry matter (Shinners, 2000). Such spoilage mainly results from high moisture content of bales during storage. There are several other factors which affect the quality of bales during storage such as weathering, storage surface, length of storage, erosion, ultraviolet degradation, bale density, and bale orientation (Wiselogel et al., 1996). Weathering and biochemical reactions which occur during storage may produce chemical compounds that affect the conversion process and efficiency of feed stocks to ethanol. Several studies (Coble and Egg, 1987; Cundiff and Marsh, 1996; McLaughlin and Adams Kszos, 2005; Monti et al., 2009; Russell and Buxton, 1985; Sanderson et al., 1997; Wiselogel et al., 1996) of the storage of forage materials have shown a significant change in dry matter, and structural and nonstructural carbohydrate content of stored forage biomass. The studies conducted so far are mostly concerned with the forage quality and its digestibility by ruminants. Forage quality tests for ruminants are generally quantitative in nature, and they usually provide nonselective information about the composition of forage material. Therefore, the tests not germane for the biofuel production processes are omitted in this study. This study was conducted to give a field demonstration in the South Central Oklahoma region. The bales were stored under different storage treatments and their affect on dry matter loss and variation in chemical composition was evaluated.
Materials and Methods Forage sorghum (Sordan Headless variety) was harvested at Oklahoma State University’s South Central Research Station at Chickasha in July 2008 and was allowed to field dry for 3 weeks. The sorghum was baled into eight round bales (estimated average weight, 450 kg per bale) and eight square bales (estimated average weight, 580 kg per bale). Four treatments with two replications were considered in the study. In three treatments, square and round bales were stored outside on pallets, on the ground and on pallets covered with tarp. A fourth treatment was stored inside in an enclosed building. Each bale was wrapped with plastic twine. Before storage all bales were weighed and samples for moisture and chemical analysis were taken using a core sampler attached to an electric drill. Average bale density for round and square bales was 112.5 kg/m3 (7.02 lb/ft3) and 163.4 kg/m3 (10 lb/ft3) , respectively. Bale moisture content ranged from 8.46 to 13.62 % with an average of 10.11% (wet basis) and was determined by the oven drying method. All the bales were stored on a well drained surface and the bale rows were oriented in the north-south direction to receive maximum sunlight. Bales were spaced approximately 1.5 m apart from each other for good air circulation and better sunlight exposure between the bales. The individual polyethylene tarps used to cover half of each of the round and square bales were 11 ft and 12 ft in width, respectively. Wooden pallets used in the treatments kept the bales about 15 cm above the ground. Variations in weights were recorded after each month of storage by lifting the bales using a tractor and transporting them to the scale. Average moisture content after each month was recorded by a handheld moisture meter, Delmhorst FX- 2000. The six month storage study was completed on January 7, 2009. Samples were evaluated for forage quality using near infrared reflectance spectroscopy at OSU Soil, Water and Forage Analytical Laboratory, Stillwater. Rainfall at the site was about 26.89 cm (10.59 in) during the storage study. Chemical Analysis of Sorghum Samples Sorghum samples were oven dried at 65 ºC for 48 h and the samples were weighed for moisture content evaluation. Samples were ground and passed through 1.0 mm screen for ADL (Acid Detergent Lignin), ADF (Acid Detergent Fibre), protein, minerals content and ash analysis. Crude proteins in forage include mixtures of true proteins (composed of amino acids) and non protein nitrogen. The crude protein in the samples was found by multiplying the nitrogen content by a factor of 6.25 (Hames et al, 2008) . The ADF fraction contains cellulose, lignin and heat damaged proteins. Lignin is another component found in cell walls of forage materials and was determined by using standard ADL procedures. Statistical Analyses Dry matter loss data was statistically analyzed by using Completely Randomized Design in SAS, and crude protein, ADL, ADF, ash and mineral content data was analyzed by using paired t- test by comparing the initial and final values for each treatment of storage using SPSS 16 for Windows.
Results and Discussion Sorghum Storage Dry matter loss during storage of sorghum bales by different storage methods is shown in Table 1 and Figure 1. Dry matter loss for round and square sorghum bales stored inside the enclosed building was 4.67 % and 5.56 %, respectively. Dry matter loss in round and square bales stored outside on the ground was 8.20 % and 12.6 %, respectively. However, the difference was not statistically significant (Table 1). Direct contact of the bale bottom surface with the ground appears to be the major deteriorating factor. Statistical analysis showed that there was no significant difference observed for dry matter loss between different storage methods except between round bales stored inside and square bales stored outside on the ground. Among all of the storage methods, the minimum and maximum dry matter loss was observed for round bales stored inside and square bale stored outside on ground without tarp, respectively (Fig. 1). Square bales lost higher dry matter because of their typical geometry and their tendency to hold moisture for a longer time. The round bales on the contrary loose moisture more quickly than the square bales. No significant difference was observed between the round and the square bales when compared statistically, but visually square bales showed more signs of weathering than round bales. The bales stored inside had no signs of visibly weathered layers whereas the bales stored outside showed varying amounts of visibly weathered layers, depending upon the storage method used, i.e. covered with plastic tarp or uncovered. The depth of the weathered layer increased slowly with the storage period and the amount of precipitation it received during storage. Although there was no statistical difference between bales stored on pallets and on the ground, the bales that were in contact with the ground had a wet, rotten and damaged bottom surface. This deterioration was not observed in the bales that were stored on wooden pallets. Coble and Egg (1987) also found higher dry matter losses for bales stored outside. Rainfall and other environmental factors are generally responsible for high dry matter losses in bales stored outside without protection. Unprotected outside storage increases moisture content in bales by creating a favorable environment for microbial growth and also results in leaching of desirable soluble carbohydrates. This results in spoilage and high dry matter loss in bales. Environmental deterioration of bales can be reduced by using polyethylene tarps or other covering materials. Even though the dry matter losses were not statistically different, the use of inexpensive storage alternatives is highly desirable to prevent weathering of bales. At the end of the storage period, the bales which were stored on the ground showed more shattered losses due to damage caused during transportation. The bales stored on the ground lost their compactness at the end of the storage period whereas bales which were stored on pallets were still in good shape.
Table1. Affect of various storage methods on dry matter loss of sorghum bales after 6 months of storage period. Dry matter loss
Storage Method Round Inside
On Pallet and covered with tarp
On Pallet and covered with tarp
*Means followed by the same letter are not significantly different at the 0.05 level as indicated by t test 14
Figure1. Affect of various storage methods on dry matter loss of sorghum bales after 6 months of storage (Where R-Inside is the round bales stored inside, R-O-Pallet is the round bales stored outside on pallets, R-O-Ground is the round bales stored outside on ground, R-O-PTarped is the round bales stored outside on pallets and covered with tarp, S-Inside is the square bale stored inside, S-O-Pallet is the square bale stored outside on pallet, S-O-Ground is the square bales stored outside on ground and S-O-P-Tarped is the square bale stored outside on pallet and covered with tarp)
Chemical Analysis of Stored Sorghum Bales Results for the chemical analysis of sorghum bales stored for 6 months under different storage conditions are shown in Tables 2 and 3. Round bales stored on the ground showed a significant decrease in crude protein content from 9.15 % to 7.92 %. There were significant differences observed for two treatments in their ADF contents. Round bales stored inside, and round bales stored outside on pallets and covered with tarps showed a significant increase in ADF content which varied from 31.67 % to 44.52 % and 35.42% to 40.34 %, respectively. Usually ADF contents increase as the storage period increases due to exposure to adverse environmental conditions like sunlight and rainfall. These results were in accordance with the results obtained by other researchers (Russell and Buxton 1985; Turner et al. 2003). The lignin content increased in general for all the stored bales but the increase was significant for square bales that were stored inside. The initial lignin content for square bales varied from 5.55 % to 7.6 %, whereas the final lignin content varied from 7.98 % to 11.72 % (Table 2). This result was in accordance to the study done by Wiselogel et al (1996). They observed an increase in ADL content from 21.4 % to 23% for switchgrass samples stored for 26 weeks. Cellulose content was also calculated by taking the difference of ADL values from ADF values. A general increase in cellulose content was observed for all the sorghum samples, none of which were significantly different from the initial values. Before storage, the cellulose content varied from 25.8 % to 37.55%, and after storage it varied from 32.8% to 38.96 %. Significant differences in ash content were observed only for square bales stored on the ground. Ash content varied from 7.61% to 13.49 % initially and 7.22 % to 10.9 % in final samples (Table 2). Mineral contents of forage materials were least affected during the storage period. Their concentrations usually increase with storage because the other constituents like non-structural carbohydrates and other extractives usually decrease with an increase in storage time. There was no significant difference observed for phosphorus, calcium, potassium, magnesium and sulphur contents before and after storage. Potassium content increased from 2.15 % to 3.05 % (Table 3). Magnesium content ranged from 0.32 % to 0.67 % initially and 0.36 to 0.73 % in samples after storage. Sulphur content ranged from 0.09 % to 0.11 % initially and 0.09 to 0.12 % in the final samples. Relationship of Storage Study with Energy Applications The loss of dry matter content during this six month storage study showed a potential economic concern for the biofuel conversion process. Non-structural carbohydrates are easily dissolved in rain water and leach into the soil. These non-structural carbohydrates can otherwise be easily converted to ethanol (Wiselogel et al. 1996). Economics of the bioethanol production process can be improved if leaching of these soluble carbohydrates can be reduced. Lignin also affects the overall biochemical process as it holds the carbohydrates and makes them unavailable for hydrolysis. The lignin content usually increases if the bales are exposed to adverse environmental conditions. Therefore, inexpensive protection alternatives like covering the bales with polyethylene tarps and storing them on pallets can reduce the dry matter loss as well as the loss of other chemical compounds that are important for conversion.
Table 2. Effect of various storage methods on initial and final contents of CP, ADF, ADL and Ash of sorghum bales after a storage period of 6 months Storage Method
On Pallet and covered with tarp
On Pallet and covered with tarp
* Significant at the 0.05 probability level, using paired t-test comparing initial and final values for each storage method Table 3. Effect of various storage methods on initial and final content of phosphorus, calcium, potassium, magnesium and sulphur of sorghum bales stored for a period of 6 months Storage Method
On pallet, covered with tarp
On pallet, covered with tarp
* Significant at the 0.05 probability level, using paired t-test comparing initial and final values for each storage method
Conclusions The study conducted was a field demonstration project to show the effect of various storage methods on the dry matter loss of sorghum bales when stored for six months. Various chemical tests were performed on the initial and final stored samples to see the effect of different storage treatments. Since the work started as a field demonstration project, two replications of each treatment were used depending upon the amount of raw material available at that time. Round and square bales were stored inside an enclosed building, outside on the ground, on wooden pallets and outside on pallets covered with tarps. A significant difference was observed for dry matter loss of round bales stored inside and square bales stored outside on the ground. Round bales stored inside lost the minimum amount of dry matter whereas square bales stored outside on the ground lost the maximum. There was a significant decrease between initial and final crude protein content for round sorghum bales stored outside on the ground. ADF content increased significantly for round bales stored inside and round bales stored on pallets and covered with tarp. ADL content also increased with storage and significant increase was observed for square bales stored inside. There was no significant change observed for mineral content in the bales. Ash content decreased in general, showing a significant decrease in square bales stored on the ground. Acknowledgements The authors would like to thank OSU”s Soil, Water and Forage Testing Lab for doing the chemical analysis test on sorghum samples and the OSU South Central Experiment Station for providing the biomaterial for this study.
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