1a. Objectives (from AD-416)
Our overall goal is to develop a productive, efficient, and sustainable biomass feedstock supply system using perennial grasses and legumes as a primary feedstock. This project addresses critical needs for feedstock development using perennial grasses and legumes by developing innovative ways to fractionally harvest and store these feedstocks. Specific objectives are: 1) design and fabricate new harvesting mechanisms to separate the high-protein and high-fiber fractions from these crops at harvest; 2) quantify the machine's field performance using a controlled set of operating variables; 3) use this information to improve the mechanisms through re-design during the off-season; and 4) collaborate to develop on-farm storage and pretreatment systems to preserve and add value to both the high-protein and high-fiber fractions. Additional objectives in the extended project include: 5) determine storage characteristics of switchgrass & reed canarygrass stored under anaerobic conditions in bunker & bag silos at different moisture contents; 6) quantify packing density, porosity & temperature profile of biomass materials during storage; 7) determine aerobic stability of stored feedstocks; 8) assess composition & bioconversion potential of feedstocks before & after storage under various conditions; & 9) estimate storage costs under different conditions, taking into account storage losses & changes in quality, as well as bioconversion potential of the stored material.
1b. Approach (from AD-416)
Design and fabricate equipment for field-fractionation of bioenergy crops during harvest. Test equipment on established fields of alfalfa, switchgrass, and reed canarygrass. Determine yield and quality of fractions obtained, along with power requirements and operating costs. Improve design of equipment to improve performance, reliability, and operating costs. Store harvested materials under different conditions, and determine dry matter losses and quality changes resulting from storage under these methods.
3. Progress Report
Research on the harvesting of perennial forages was conducted by the University of Wisconsin-Madison. Research conducted for the reporting period concentrated on single-pass fractional harvest of alfalfa, switchgrass and reed canarygrass. An experimental harvest fractionation attachment for a self-propelled forage harvester was designed and fabricated. The leaves of biomass plants were stripped by a multi-tine rotor similar to that used to strip snap beans. The stripped leaves and upper plant parts were captured in an auger, processed by the forage harvester cutterhead, and then collected in a trailing wagon. Directly behind and below the stripping rotor was a cutterbar that cut the stems and formed them into a windrow underneath the harvester. The yield of the stripped fraction was dependent upon rotor:ground speed ratio and rotor:plant height ratio. The latter ratio had a much greater impact on the yield of the stripped fraction than did the former ratio. Fractionation was more easily accomplished for alfalfa than for reed canarygrass or switchgrass. Varying plant height and lodging caused difficulties in reed canarygrass. Switchgrass was especially difficult to fractionally harvest because the brittle stems of this plant were too easily broken by the stripping rotor, which caused the stems to entangle in the rotor, eventually rendering the mechanism inoperable. The protein content of the stripped fraction averaged 23.1%, 8.9%, 7.1% for alfalfa, reed canarygrass, and switchgrass, respectively. The protein content of the cut stem fraction averaged 12.0%, 4.0%, 3.7% for alfalfa, reed canarygrass, and switchgrass, respectively. In alfalfa, the stripping rotor removed 40% more material than the estimated leaf mass (estimated by hand sampling prior to harvest). It was observed that the rotor removed not only the leaves, but also the top portion of the stem, which accounts for the recorded mass difference. The rotor removed only 1% more mass than the estimated leaf mass of reed canarygrass, indicating that most of the stripped mass was leaves. The rotor removed 100% more material than the estimated leaf mass in switchgrass, which was caused by brittle stems breaking off and being harvested in the stripped fraction. The moisture content of the stripped fraction for the two perennial grasses averaged 63.5% (w.b.), which should produce successful direct ensiling. The alfalfa leaves averaged 77.1% (w.b.) moisture, so direct ensiling would only be possible with appropriate amendments or additives. Stripped alfalfa material was made available periodically to ARS scientists to conduct lab-scale experiments on direct ensiling of the stripped fraction. The cut fraction, consisting mainly of stems, dried quite readily to either chopping or baling moisture because the stripping rotor removes some of the waxy outer layer of the stem, facilitating egress of water from the stems. Progress was monitored by the ADODR through frequent telephone conversations and face-to-face meetings.