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ACCESSION NO: 0414306 SUBFILE: CRIS 

PROJ NO: 5090-41000-006-02S AGENCY: ARS 3655 

PROJ TYPE: USDA COOPERATIVE AGREEMENT PROJ STATUS: NEW 

START: 02 SEP 2008 TERM: 01 SEP 2013

INVESTIGATOR: WEIMER P J

PERFORMING INSTITUTION:

UNIV OF WISCONSIN 

21 N PARK ST STE 6401 

MADISON, WISCONSIN 53715-1218

NOVEL TECHNOLOGIES FOR FIELD FRACTIONATION, HARVESTING AND STORAGE OF

PERENNIAL BIOENERGY CROPS

OBJECTIVES: 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.

APPROACH: 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. We will also compare the yield and quality of switchgrass and reed canarygrass when

stored at different moisture levels in either bag silos (a widely adopted storage technology) or in

bunker silos (a potentially lower-cost method that does not generate plastic waste). Conventional

measures of silage preparation (packing density, porosity, temperature profiles) will be combined with

measures of microbial conversion in the silo (fermentation acid production), and of subsequent

bioconversion potential of feedstock after storage to fuels and fuel precursors. Because exposure of

anaerobically stored feedstocks to air can cause undesirable spoilage by microorganisms, we will

conduct aerobic stability tests to determine if storage method affects the rate and extent of feedstock

spoilage, and if different microbial agents are responsible for spoilage of different feedstocks stored

under different conditions. We will estimate costs of storage of each feedstock that will take into

account the dry matter losses and quality change of each feedstock during storage, and the

bioconversion potential after storage.
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PROGRESS: 2012/10 TO 2013/09

Progress Report 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 highprotein 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. 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. We will

also compare the yield and quality of switchgrass and reed canarygrass when stored at different

moisture levels in either bag silos (a widely adopted storage technology) or in bunker silos (a

potentially lower-cost method that does not generate plastic waste). Conventional measures of silage

preparation (packing density, porosity, temperature profiles) will be combined with measures of

microbial conversion in the silo (fermentation acid production), and of subsequent bioconversion

potential of feedstock after storage to fuels and fuel precursors. Because exposure of anaerobically

stored feedstocks to air can cause undesirable spoilage by microorganisms, we will conduct aerobic

stability tests to determine if storage method affects the rate and extent of feedstock spoilage, and if

different microbial agents are responsible for spoilage of different feedstocks stored under different

conditions. We will estimate costs of storage of each feedstock that will take into account the dry

matter losses and quality change of each feedstock during storage, and the bioconversion potential

after storage. This research is related to Objective 2 of the parent project: Develop new commercially

viable technologies for harvest, storage and/or on-farm pretreatment and biorefining of perennial

bioenergy crops, and use modeling to assess the economic and environmental impacts of integrating

these new technologies into sustainable farming system. Research was conducted by the cooperator

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.

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 collected in a trailing wagon. A cutterbar cut the stems and formed them

into a windrow underneath the harvester. Stripped fraction yield depended on 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 the plant were

easily broken by the stripping rotor, causing the stems to entangle in the rotor and eventually

rendering the mechanism inoperable. Crude protein (CP) content of the stripped fraction averaged

23.1%, 8.9%, and 7.1% for alfalfa, reed canarygrass and switchgrass, respectively. CP content of the

cut stem fraction averaged 12.0%, 4.0%, and 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) . 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%
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more mass than the estimated leaf mass of reed canarygrass, indicating that most of the stripped

mass was leaves. In switchgrass, the rotor removed 100% more material than the estimated leaf

mass. Moisture content of the stripped fraction for the two perennial grasses averaged 63.5% [wet

basis (w.b.)], which should produce successful direct ensiling. Alfalfa leaves averaged 77.1% (w.b.)

moisture, so direct ensiling would only be possible with appropriate amendments or additives.

Stripped alfalfa material was used by the ARS scientist to determine storage characteristics of directensiled leaves. The cut fraction (consisting mainly of stems) dried readily to either chopping or baling

moisture because the stripping rotor removed some of the waxy outer layer of the stem, facilitating

evaporation of water from the stems. The cooperator also helped collect data during field evaluation of

an experimental leaf stripper designed/fabricated by ARS scientists, in order to characterize the

optimum performance configuration of the leaf stripping rotor. The cooperator also evaluated a new

wide-body leaf stripper on alfalfa that was designed/fabricated by ARS scientists. The harvested

leaves will be used for a feeding trial in late 2013. Research was also conducted on anaerobic storage

and aerobic stability of moist perennial grasses. These crops are typically harvested in the late fall

when drying conditions are difficult. Delay of harvest until spring can insure a dry-standing crop, but

winter losses often exceed 15% of crop dry yield. Biorefineries require a consistent feedstock, but

bales stored outdoors can have highly variable moisture and quality. Indoor storage overcomes this

problem, but adds significant cost. Reed canarygrass and switchgrass were harvested at two moisture

contents (~54 and 43% w.b.) and stored in pilot-scale silo bags until late spring. Loss of dry matter

(DM) during storage ranged from 2.3% to 3.4%, with an average across all treatments of 2.3%. There

was no significant difference in storage losses between high- and low-moisture treatments. Both

grasses were removed from storage with uniform moisture through the cross section and length of the

bag. Moisture content at removal only varied 1 to 2 percentage units from the harvest moisture.

Aerobic stability was determined during 2- and 7-day aerobic exposure after removal from storage

whereby losses of 1.6% and 2.3% of DM, respectively, occurred. Lactobacillus buchneri was applied

as a bacterial inoculant at the time of harvest to improve aerobic stability of the grasses. The inoculant

was successful in reducing the heating degree days and temperature rise above ambient in both

grasses during aerobic exposure. L. buchneri also produced significantly lower counts of undesirable

yeast and mold than did the control. Inoculation did not have a significant effect on DM loss during

storage or aerobic exposure. This system offers a wider harvest window, produces a size-reduced

material at time of harvest, and well-conserved feedstock DM aerobic stability, especially when

inoculated with L. buchneri.

PUBLICATIONS (not previously reported): 2012/10 TO 2013/09

No publications reported this period.