An ASABE Meeting Presentation Paper Number: 131574361 Sugarcane Harvesting System: a Critical Overview Shaochun Ma, Manoj Karkee, Qin Zhang Washington State University Center for Precision & Automated Agricultural Systems, Prosser, WA 99350, USA Written for presentation at the 2013 ASABE Annual International Meeting Sponsored by ASABE Kansas City, Missouri July 21 – 24, 2013 Abstract. In this paper, a critical literature review of sugarcane harvesting systems in the context of sugar and biofuel production is conducted. For sugar production, sugarcane field burning is carried out worldwide before harvesting to get rid of leaves and tops which would impede the harvest operation. However, field burning has environmental consequences. Hence, the improvement in harvester performance will have an effect on costeffectiveness and sustainability of sugarcane production and also on the success of biofuel production. Sugarcane is one of the most efficient biofuel feedstocks in commercial use. Harvest cost comprises a major component of overall sugarcane production cost. We surveyed the merits and limitations of chopped billet and whole stalk harvesting systems. Whole stalk harvesting can reduce juice loss and sugar deterioration while chopped billet harvesting has higher efficiencies in handling high-tonnage and bent stalks. Moreover, new technologies and innovations applied on cane harvesters for improving harvesting efficiencies and qualities are investigated. Finally, major issues requiring further research are identified and corresponding recommendations are made for future studies. Analyzing the current issues and challenges, the main outcome of this review is the identification of potential solutions that can be investigated to improve sugarcane harvesting efficiency. Effective and efficient harvesting can make sugarcane production more viable, profitable and sustainable, especially for biofuel use since it requires collecting both of stalks and trash. Keywords. biofuel feedstocks; sugarcane harvesting; environmental consequences; cost-effectiveness; sustainability Introduction Sugarcane originates from tropical South Pacific and the planting techniques were transferred to China, North Africa, Spain, and America in 7th and 8th century (Fischer et al., 2008). According to World Crop and Livestock Statistics published by the Food and Agriculture Organization (FAO) since 1950, world sugarcane growing area The authors are solely responsible for the content of this meeting presentation. The presentation does not necessarily reflect the official position of the American Society of Agricultural and Biological Engineers (ASABE), and its printing and distribution does not constitute an endorsement of views which may be expressed. Meeting presentations are not subject to the formal peer review process by ASABE editorial committees; therefore, they are not to be presented as refereed publications. Citation of this work should state that it is from an ASABE meeting paper. EXAMPLE: Author’s Last Name, Initials. 2013. Title of Presentation. ASABE Paper No. ---. St. Joseph, Mich.: ASABE. For information about securing permission to reprint or reproduce a meeting presentation, please contact ASABE at rutter@asabe.org or 269-932-7004 (2950 Niles Road, St. Joseph, MI 49085-9659 USA). increases from 6.3 million hectares to 25.4 million hectares (FAOSTAT, 2013). Before mechanical harvesting, the sugarcane harvesting is labor-intensive which is done manually by various types of hand knives. Sugarcane workers can easily get fatigued due to excessive stress on the joints and muscles (Clementson and Hansen, 2008) and have safety issues because of harmful pests from plantations (Carvalho, 2012). With the advent of sugarcane harvester, the productivity (acre/hr) is increased substantially and the costs are reduced compared to manual harvesting. However, harvesting still remains to be one of the most costly operations representing about 30% of total sugarcane production cost (Barker, 2007; Salassi, 2006; Salassi and Barker, 2008). In some places, such as Hawaii, the field conditions become more challenging for mechanical harvesting because of uneven terrain, rocky land and lodging problem. Harvesting cost will be much higher in these places since considerable work is required to prepare the field and modify commercial harvesters to be applicable to local field conditions. Furthermore, the production cost is a big barrier to the commercialization of biofuel produced from sugarcane biomass feedstocks. Therefore, it is meaningful to improve harvester performance and reduce harvesting operation cost which could help decrease the biofuel production cost. . The sugarcane chopper harvester and whole stalk harvester are two main technologies available today. The chopper harvester introduced stalk chopping into pieces and saved one extra operation (i.e. uploading windrowed stalks to wagon). However, chopped billets have more cutting area exposed to air leading to more juice/sugar deterioration than whole stalk (Maleki and Jamshidi, 2011). The whole stalk harvesters are still popular in areas with erect cane conditions because of low cane deterioration rate than cane billets (Lionnet, 1986). The disadvantage of whole stalk harvesting is that it cannot handle the lodging and bent canes (Spargo and Baxter, 1975). Biofuels, such as sugarcane ethanol, has 78% less Greenhouse Gas (GHG) emission than petroleum gasoline and the GHG emission will be reduced additional 9% with the elimination of cane field burning (Wang et al., 2008). Pre- and post-harvest burning is one of major contributors to sugarcane ethanol related GHG emission and it is going to be phased out in future due to people’s global warming concerns. . In addition to releasing CO2, sugarcane burning also results in acidic fine article emission, which has negative impact on air quality and human health (Allen et al., 2004). The green cane harvesting, which is harvest sugarcane without openfield burning, presents environment benefits. However, its expansion in main sugarcane production region depends on the improvements of harvesting technology because the machine needs to process more biomass throughput than burnt cane. . The issues and challenges with respect to high operation costs, juice/sugar deterioration, adaption to various field condition and environmental consequences have been studied in the literature. It is necessary to comprehensively review the relevant literature regarding these topics, so as to identify the merits and limitations of current commercial sugarcane harvesting systems. This is the purpose of this review. In addition, the review provides recommendations for future development based on the analysis of current stateof-the-art. Sugarcane harvesting preparation Pre-harvest burning is usually carried out before sugarcane harvesting which makes the process easier during both manual and mechanical harvesting. Cane burning is conducted during the whole harvesting season and most of trash, including tops and leaves, is burned off because of increased biomass throughput of green harvesting and the more flexible operations (cutting, chopping, and conveying) (Rípoli, 2000). However, preharvest burning becomes one of the most sensitive environmental issues faced by local communities. In recent years, governments are formulating relevant regulations, such as incentives, to help farmers switch from burnt cane harvesting to green cane harvesting. Green cane harvesting has presented obvious environmental benefits and it is the trend of cane harvesting process due to the less GHG emission. The transition from burnt cane harvesting to green cane harvesting makes tops and leaves separated from stalks that forms a surface trash blanket. The green cane trash blanketing (GCTB) not only increases soil nutrient content, but also it is resulted in better moisture retention and weed control (Page et al., 1986; Robertson and Thorburn, 2007; 2013 ASABE Annual International Meeting Paper Page 1 of 12 Wood, 1991). The adoption of green harvesting is determined by the improved machine performance of harvesters. Moreover, adaptable agricultural technologies and appropriate field preparation are needed to make sugarcane harvesting more efficiently and effectively. Burnt cane harvesting Farmers conduct sugarcane burning as a standard pre-harvest practice throughout the world because it leads to reduced pest stress and reduced cost of tops and trash handling (Boeniger et al., 1991; Humbert, 1963; King et al., 1953; Semenzato, 1995). In addition, cane burning can get rid of trash which leads to increased fiber and non-sucrose dissolved substances affecting the concentration of sucrose during sugar extraction process (Bernhardt et al., 2000; Lionnet, 1986). However, the cane burning has various negative impacts in the sugar yield. One of shortcoming is that there is a risk of saccharose deterioration reducing the rate of sugar extraction. Therefore the burnt cane has to be processed within 15 days to avoid the fermentation of saccharose to ethanol (Semenzato, 1995). Micro-organisms play an important role in cane deterioration. Cane burning facilitates the micro-organism infection with wax removal, cane splits, and juice leakage (Lionnet, 1986). In recent years, public pressure against cane burning is increasing throughout the world because of growing environmental consciousness. In 1991, Boeniger et al. performed a survey and personal air sampling to characterize worker’s exposure to biogenic silicate fibers. The survey and sampling showed that the air concentration of biogenic silica fibers around harvesting workers was 56,000 fibers/m3 during harvesting season (Boeniger et al., 1991). As a result of public concerns, US National Institute for Occupational Safety and Health (NIOSH) investigated the disease risks of sugarcane workers exposed to biogenic silica fibers. The reason is that biogenic silica fibers are found in sugarcane leaves and it is known as a causative agent to esophageal cancers (Newman, 1986). In Brazil, Gisela and et al. (2008) reported that Polycyclic Aromatic Hydrocarbons (PAH) content and mutagenic activity of organic extracts increase extensively because of cane burning, cutting, and transporting in San Paulo State during sugarcane harvesting season. Green cane harvesting Figure 1. Green cane harvesting by John Deere 3522 sugarcane harvester Considering the environmental effect, green cane harvesting could represent a sustainable management option for sugarcane harvesting. The residues left in field from green harvesting can control weeds, reduce soil water loss, decrease soil erosion, and improve nutrient cycling, soil quality, and productivity (Braunbeck et al., 1999). In 2008, Núñez and Spaans reported that the weed control and irrigation costs after green harvesting were reduced by 35% and 10% respectively (Núñez and Spaans, 2008). The soil fertility can be enhanced by increased soil C and N content by 0.47 and 0.07 Mg/ha/year under green cane harvesting management (Cerri and Cerri, 2007; Galdos et al., 2009; Goldemberg et al., 2008). From the standpoint of biofuel production, the residues can be collected as biomass feedstocks. At this point, the investigations will be necessary to study the tolerable removal rates of biomass residue from agricultural land that compromises soil sustainable management (Karkee et al., 2012). However, the expansion of green cane harvesting depends on the sugarcane mechanical harvesting technology improvement. There are several challenges faced by mechanical 2013 ASABE Annual International Meeting Paper Page 2 of 12 green cane harvesting: (1) increased extraneous materials (such as mud, debris); (2) decreased cane throughput because of trashes; and (3) increased harvesting cost. Comparing green cane and burnt cane harvesting, Eiland and Clayton (1983) evaluated the fuel consumption and machine performance of four mechanical harvesting systems in Florida and found that the fuel consumption was increased by 12% and the harvesting efficiency (recovery rate) was decreased by 17%. Merits and weaknesses of burnt and green cane harvesting management systems are summarized in Table 3 below. Table 1. Green cane vs. burnt cane harvesting systems Management System Pros Cons (1)Reduced trash handling cost; and (2)pest control (1)Sugar deterioration; and (2) environmental consequences of air emission (Boeniger et al., 1991; Humbert, 1963; King et al., 1953; Semenzato, 1995; Bernhardt et al., 2000; Lionnet, 1986) (Semenzato, 1995; Lionnet, 1986; Boeniger et al., 1991; Brazil, Gisela and et al. 2008) (1)Water and soil conservation; and (2)weed control; reduction of pollutant emissions (1)Harvesting efficiency affected; and (2)harvesting cost increased (Braunbeck et al., 1999; Núñez and Spaans, 2008; Cerri and Cerri, 2007; Galdos et al., 2009; Goldemberg et al., 2008) (Eiland and Clayton, 1983) Burnt cane harvesting Green cane harvesting Sugarcane harvesting technologies Sugarcane can be harvested manually and mechanically. Harvesting sugarcane manually is a very laborintensive activity and agricultural labors are becoming scarce. The advent of mechanical harvesting frees harvesting labors from drudgery field operations. Harvesting sugarcane mechanically makes green harvesting possible since almost all manual harvested cane fields are burned to reduce labor cost (Han et al., 2012). Not only is mechanical harvesting more productive, it also reduces greenhouse gas emissions from pre-harvest burning of spiky leaves and tops necessitated by manual harvesting (Braunbeck et al., 1999). In addition, the adoption of new technologies, such as GIS, GPS and sensing technologies on sugarcane harvester makes the machine more cost-efficient, productive, and adaptable to various field conditions (Goswami et al., 2012). Harvesting modes Based on the form of harvested stalk, sugarcane harvesting can be categorized into two categories: billet harvesting and whole stalk harvesting systems. The development of sugarcane harvesting machines can date back to late 19th century (Spargo and Baxter, 1975). During the early period in Australia, the harvester is consisted of cutting device, elevating system and knives severing the tops (King, 1969). . The earlier harvester models were developed to process whole stalks. Later, a different harvesting mode was invented and a sugarcane chopper harvester was commercialized due to the limitations of soldier (whole stalk) harvester harvesting lodging and bent sugarcanes. The new harvesting concept was applied to new harvesters which chop stalks into billets after base cutting and topping. Currently, sugarcane chopper harvester has been the predominant model in the world, but whole stalk harvesting method are still employed in places (e.g. Louisiana) where canes are mostly standing upright (Salassi and Champagne, 1996). Whole stalk harvesting Compared to chopped cane harvesting, whole stalk harvesters cut canes at the base and whole stalks are conveyed to the field ground then arranged into a windrow for subsequent loading. Normally, post-harvest burning is carried out to get rid of the trash such as leaves and tops before windrowed stalks being transported to processing plant or storage site for future use (Salassi and Champagne, 1996). With erect stalks and wet growing weather (cane chopper harvester could result in higher and mud levels), soldier (whole stalk) harvester has been successfully used in Louisiana (Salassi and Champagne, 1996). Louisiana whole stalk harvesting 2013 ASABE Annual International Meeting Paper Page 3 of 12 system (whole stalk harvester) is the main type of technology from which other similar harvesting systems are derived (Braunbeck et al., 1999). In addition, post-harvest deterioration of sugarcane (sucrose, glucose, and fructose) has been investigated in the past by previous studies. The state of the stalk, such as whole stalk and billets, influences the cane deterioration rate during the cut-to-crush delay (Lionnet, 1986). Whole stalk harvesting method has advantages in reducing the sugar/juice deterioration rate because of limited cutting section area exposed to atmosphere which decreases the chances of organisms entering the stalk. In 2003, Singh and Solomon reported that whole stalk had lower deterioration in terms of percentage of sucrose in juice and juice pH value. Seven days after harvesting, whole stalk canes had 5.3% less loss in cane weight compared to cane billets (Singh and Solomon, 2003). The limitation of this mode is that the conveying system cannot handle bent stalks of lodged sugarcane and has difficulties in harvesting heavy tonnage cane (Salassi and Champagne, 1996; Spargo and Baxter, 1975). For lodged canes, the stalks are bent and twisted into various shapes which are challenging to form compact bundles for being loaded to a wagon (Spargo and Baxter, 1975). Under the condition of high tonnage canes with lodging issues, the cane recovery rate for a soldier harvester will be substantially declined because of its limitations to handle bent canes. Billet harvesting Figure 2. Harvested sugarcane stalks in billet forms The advent of billet harvesting is because whole stalk harvester cannot handle the bent or lodged canes well. After base cutting and topping, the stalks are chopped into billets which have a uniform size for easily handling. Wagons run along with the harvester for loading chopped billets directly which saves one more working procedure. Compared to billet harvesting, whole stalk harvesting needs other sugarcane equipment to pick up the windrowed sugarcane stalks to wagons. In 1955, Ken Gaunt, an Australian engineer, proposed the concept of chopping cane into pieces after base cutting due to the material handling problem of soldier harvesters (DIISRTE, 2011). Gaunt led a team to fabricate the first sugarcane chopper harvester leading to a basic technology (Spargo and Baxter, 1975). Later, other similar harvesting systems are derived from this technology (Spargo and Baxter, 1975; Braunbeck et al., 1999). If sugarcane harvesting is defined to include all relevant operations to collect stalks from the field, the sugarcane chopper harvester can be called “complete” harvesters while the whole stalk harvesters can only be called “partial” harvesters (Burrows and Shlomowitz, 1992). The disadvantage is that chopping process accelerates sugar deterioration and increases the sugar loss because of the easy access of bacterial through abrasion, failure points and cutting end surfaces in chopped 2013 ASABE Annual International Meeting Paper Page 4 of 12 billets. The harvested billets need to be milled as fast as possible. Studies conclude that the ideal sugar quality can be maintained within 24 hours which makes the tighter schedule of cane shipment and processing (Burrows and Shlomowitz, 1992). In addition, there also exists juice loss during cutting and chopping operations because cane juice is squeezed out from the torn cells (Maleki and Jamshidi, 2011). Cane juice loss leads to the reduced sugar yield and higher operation cost (Maleki and Jamshidi, 2011). Harvesting scale The capacity of sugarcane harvester is determined by the swath: (single-row or double-row) of cutting head. Under the condition of same harvesting technology, double-row whole stalk harvesters have less operation cost of single-row whole stalk harvesters (Salassi and Champagne, 1996). In 1996, Salassi and Champagne compared the estimated performance rating for single-row whole stalk harvester, double-row whole stalk harvester, single-row sugarcane chopper harvester, loader (combine harvester), transloader (whole stalk harvester). Table 1. shows the operation costs for these three harvesters. Although the cost per hour for single-row whole stalk harvester is 35% less than double-row whole stalk harvester, the cost per acre will be 69% less than double-row harvester because the capacity (acres/hr) is 61% less (Salassi and Champagne, 1996). For single-row sugarcane chopper harvester, the cost per hour is even higher than double-row whole stalk harvester because of more working procedures and energy consumption. In past few decades, singlerow sugarcane chopper harvester had been widely used for sugarcane harvesting around the world since it is more stable and efficient for high yield variety of sugarcane (Salassi and Champagne, 1998). In 2003, Jakeway studied the application of cane and forage harvesters for biomass recovery. The average effective productivity of cane harvester (two cane line) was 9.1 (recovered yield is 93.7 Mg/ha) Mg/hr, whereas forage harvester (four cane lines) reached to 11.6 Mg/hr (recovered yield is 67.0 Mg/ha) (Jakeway, 2003). It turns out that two-time swath does not make capacity double due to the different technology. Literature does not show any operation cost estimation studies on double-row sugarcane chopper harvesters. In 2010, Deere & Company introduced their first double-row harvester model (John Deere 3522) which increases the productivity compared to the previous single-row models (John Deere 3510 and 3520) (Deere&Company, 2011). To improve the harvesting capacity and reduce the operating costs, multi-row sugarcane harvesters are the trend of harvesting technology development. Table 2. Operation costs for three harvesting systems (25-35 tons/acre) (Salassi and Champagne, 1996) Systems 1 2 3 Harvesters Single-row whole stalk Double-row whole stalk Single-row chopper $/hr Acres/hr $/acre 53.97 1.67 32.32 82.69 4.33 19.1 86.59 1.87 46.3 New technologies Automatic guidance With the revolution of electronics in last several decades, the precision farming (PA) tools such as automatic guidance technology has been successfully applied to agricultural machines. To follow desired trajectory during field operation leads to increased operation field efficiency of agricultural vehicles. The automation of machine guidance of agricultural machines can date back to 1920s (Reid et al., 2000). In 1950s and 1960s, the ‘driverless tractor’ prototypes were successfully guided by detecting the signal from the buried leader cable. Later in the mid of 1980s, machine vision guidance system with image sensors had been developed for agricultural combine harvesters for row crops (Li et al., 2009). Another technology breakthrough in this area is the application of global positioning systems (GPS). As the agricultural vehicles is driven in a field, auto-steer gathers GPS signals and steers the vehicles. GPS system plays an important role in automatic guidance of off-road vehicle. With the advent of high accuracy GPS, such as Carrier Phase Differential GPS (CDGPS), the accuracy of agricultural equipment operating had been increased to centimeter level (O’Connor et al., 1996). With GPS-aided auto guidance system installed on the machine, the farmers and operators could set up guidance paths at home and run harvesting machines according to the same guidance line (Case, 2009). The Case IH Austoft 8000 series harvester operators can control guidance using a portable monitor facilitating them 2013 ASABE Annual International Meeting Paper Page 5 of 12 to concentrate on sugarcane cutting instead of steering (Case, 2009). The auto-guidance systems technology, which had been developed in past decades, becomes mature and these commercial products are available on the market in recent years. This auto-guidance system has also been adapted to sugarcane harvesting successfully. In 2012, Baio evaluated the field performance of sugarcane harvester auto-guidance system in terms of accuracy, biomass loss, and field efficiency. Compared to manual steering systems, the field pass-to-pass accuracy has been greatly increased (Baio, 2012). Since sugarcane is a perennial crop, the harvester needs to stay on the rows and reduce the damage of ratoon. The utilization of auto guidance can help operators to avoid the damage even harvesting on night (Erickson, 2006). Yield monitor system PA technology had been widely applied to various cropping systems around the world. However, it is challenging to adopt PA in sugarcane production because there are few commercial yield monitors being used (Cox, 2002; Erickson, 2006). To overcome the bottleneck, researchers developed and tested a variety of prototype yield monitors to recognize variation of agricultural land potential productivity. Yield monitor system installed on harvesters is able to conduct yield mapping which target the management of inputs (fertilizer, water, and etc.) to the farm land (Erickson, 2006; Griffin, 2010; Jhoty and Autrey, 1999; Shearer et al., 1999). The sugarcane yield monitors can be categorized into two types based on monitoring concepts: weighing pads (direct measurement); and indirect yield estimation using chopper pressure, elevator power or optical sensors. Weighing pads have been employed by many researchers to measure the sugarcane yield. Wendte et al. (2001) developed a deflection plate sensor for sugarcane yield monitoring, which includes a deflection plate mounted nearby the billet discharge area and a load cell connected to the plate. Pagnano and Magalhaes (2001) installed the weight sensor in the upper section of cross elevator. A low-pass filter was employed to eliminate high-frequency noise. Benjamin et al. (2002) designed a similar cane yield monitoring system in Louisinana State University. In this design, the weighing plate was mounted on the floor of cross elevator. The R-Square value for the yield prediction is 0.97. Cox (2002) presented a yield mapping system for sugarcane chopper harvesters with a weigh pad sensor. The technology has been commercialized by Case IH. In 2003, Hernandez et al. introduced a biomass flow sensor coupled with the harvester roller feeder for cane mass-flow rate measurement (Hernandez et al., 2003). Indirect yield measurement includes use of optical sensors or machine power related parameters. Price et al. developed a fiber optic yield monitoring system with three optical sensors mounted in the elevator floor to estimate the sugarcane yield (Price et al., 2011). The result shows R-square value of 0.98 between the sensor readings and actual yield (Price et al., 2011; Price et al., 2007). In 1996, Cox et al. studied the relationship between billet mass flow rate and harvester power consumption showing that mass flow rate is proportional to process power. Various pressure and speed sensors were installed to measure power consumed in chopping and conveying systems. The chopping and conveying power consumption shows a linear relationship with billet mass flow rate and the R-squares are 0.96 and 0.95 separately (Cox et al., 1996). Table 3. Sugarcane yield monitor systems Approach/outcome A deflection plate sensor mounted to billet discharge area. A weigh pad was amounted in the upper section of cross elevator and a low-pass filter was used to eliminate high-frequency noises. The weigh pat was mounted on the floor of cross elevator and the R-square for the yield prediction is 0.966. A new weigh pad sensor was designed to minimize the error due to dynamic conditions, to reduce the noise due to external acceleration, and to maximize its natural frequency. A biomass flow sensor coupled with the harvester roller feeder using a displacement transmitter for biomass input measurement. 2013 ASABE Annual International Meeting Paper References Wente et al., 2001 Pagnano and Magalhaes, 2001 Benjamin et al., 2002 Cox, 2002 Hernandez et al., 2003 Page 6 of 12 A fiber optic yield monitoring system was mounted in the elevator floor to estimate cane yield and the R-square value is 0.98. Cane mass-flow rate was estimated by measuring power consumed in chopping and conveying systems. The R-squares are 0.96 and 0.95. Price et al., 2007; Price et al., 2011 Cox et al., 1996 Recent mechanical harvesting directions For traditional harvesting, the typical harvester tops the cane plants, cuts cane at the base of stalk, chops the stalk into billets (segments), and then remaining leaves are stripped off from stalks by primary and secondary extractors. However, harvesting cane with leafy trash (such as tops and leaves) will affect the quality and quantity of sugar extraction negatively (Eggleston et al., 2009). From the perspective of biofuel production, cane trash (tops and leaves) can also be used for cellulosic ethanol production since it is composed mainly of cellulose, hemicellulose and lignin which are potential sources of lignocellulosic materials and fermentable sugars (Kim and Day, 2011). The fibrous residues, such as tops and leaves, left in the field through normal harvesting contribute to about 15.1 Mg/ha which is 37% of whole cane plant dry matter and about 42% of cane plant dry matter above the ground (Deepchand, 1986). To harvest sugarcane biomass for biofuel refining, the cane residues are also needed to be collected for conversion into ethanol. In Louisiana, the cane residues left in the field are typically 6-24 Mg/ha (Viator et al., 2007). White et al. (2012) conducted research on the effects of green-cane harvesting on biomass and energy yields. The study reported that the sugarcane chopper harvester can increase dry biomass yield by up to 13 Mg/ha with slow extractor fan speed and fans turned off which is a good strategy to harvest biomass as much as possible (White Jr et al., 2012). Also in major growing areas, sugarcane tops is one of the largest biomass resources of bioethanol feedstocks since it has enough amounts of sugar monomers (six and five carbon sugars) (Dibanet, 2012; Sindhu et al., 2012). For instance, Stewart and Kingston estimated that the sugarcane residue production is 2.6 million tons in dry matter compared to 2.75 million tons sugar production in Queensland, Australia (Stewart and Kingston, 1979). In Hawaii, the average residue left after harvest is 18.2 Mg/ha (Jakeway, 2003)., Therefore, sugarcane residues, such as tops and leaves, are potential resources for energy fuel production and it is worthwhile to collect them for energy use. Based on biomass harvesting strategy for biofuel production, the tendency of cane harvester development in future is to modify the current topper and extractor mechanism for harvesting biomass as much as possible. In addition, it is necessary to modify cropping system to facilitate harvesting operation. Sugarcane grown on raised bed allows a mechanical harvester to cut stalk at or under the soil surface (Richard et al., 1991). Since the lower stem has higher level of sugar, cutting cane at ground level can harvest the bottom sugar-rich internodes and increases total sugar yield (McIlroy, 1963). Furthermore, the shape of raised-bed cane growing rows suit the base cutter to cut stalks at lower height and reduce cane damage (Hurney et al., 2005). In addition, the raised bed system controls machine traffic and avoid compaction of top soil (Govaerts et al., 2007). In Hawaii, test plantings and harvestings revealed that sugarcane mechanical harvesting requires rock-free farmland because rocks may damage the knife blades (Lee Jakeway, Hawaiian Commercial & Sugar Company, personal communication). Considerable effort has to be spent on preparing the field to remove surface and topsoil rocks for mechanical harvesting. From the perspective of cane harvesters working in the rocky field, the new machine cutting head needs to be equipped with rock detection and real-time control system which has the capacity to identify and avoid huge rocks by lifting the cutting head. In addition, preharvest cane burning is carried out to make the operation easier and more efficient. Switching to green cane harvesting, it requires higher productivity to handle more biomass under the same conditions. Conclusion and recommendations Harvesting is a crucial component of sugarcane production system. In this paper we conducted a literature review on sugarcane harvesting technologies in the context of both sugar and biofuel production. Moreover, 2013 ASABE Annual International Meeting Paper Page 7 of 12 we identified the characteristics that current whole stalk harvesters and chopper harvesters have and recommended relevant characteristics desired by sugarcane/energy cane harvesting systems for biofuel feedstock production. From the perspective of modern cane harvesting technologies, the design of more reliable and efficient harvesters goes beyond minimizing harvest cost and biomass loss and includes the consideration of minimizing negative impacts on environment and human health. The environmental issues and public pressure against cane burning must be considered in combination with machine performance improvement. The elimination of burning practices before sugarcane harvest has been and will led to more sustainable harvesting systems, green cane harvesting, which has lower impact on nearby communities and environment. Although higher harvest cost is incurred by handling increased volume of materials, the biomass recovery rate has been improved substantially and hence higher increased biofuel yield. Cane harvester design characteristics and capabilities are dependent upon the purposes of use: sugar production or biofuel production. For sugar production, the harvesters need to be able to effectively separate leaves and tops from stalks to increase the purity of extracted juice and reduce transportation cost. For biofuel production, the harvesters need to be able to harvest as much biomass as possible since all of stalks, leaves, and tops can be used as feedstocks for bio-refineries. The review identified that there is a lack of literature on sugarcane/energy cane harvesting technologies for biofuel feedstock production. In recent years, commercial harvesters that were developed for harvesting sugarcane for sugar production were used to harvest sugarcane/energy cane for research in biofuel production. In future, specialized harvesting technologies and machines need to be developed for green cane harvesting to support commercialization of cellulosic ethanol production in US using sugarcane/energy cane crops. Acknowledgements The research presented in this paper was partially supported by Biomass Research and Development Initiative (USDA-NIFA-9008-003540) and Washington State University Center for Precision and Automated Agricultural Systems. Any opinions, findings, and conclusions expressed in this paper are those of the authors, and do not necessarily reflect the views of USDA-NIFA or Washington State University. Reference Allen, A., A. Cardoso, and G. Da Rocha. 2004. Influence of sugar cane burning on aerosol soluble ion composition in Southeastern Brazil. Atmospheric Environment 38(30): 5025-5038. Baio, F. H. R. 2012. Evaluation of an auto-guidance system operating on a sugar cane harvester. Precision Agriculture 13(1): 141-147. Barker, F. G. 2007. An economic evaluation of sugarcane combine harvester costs and optimal harvest schedules for Louisiana. MS thesis. Baton Rouge, La.: Louisiana State University, Department of Agricultural Economics and Agribusiness. Benjamin, C. E. 2002. 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