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Researchers study shapes of switchgrass bales

If you choose a rectangular baler to harvest switchgrass in the future, it might be a good idea to cover the harvested bale. According to an evaluation of two shapes of switchgrass bales presented at the Milan No-Till Crop Production Field Day, in Milan, Tenn., rectangular bales exposed to extensive weathering absorbed over half their original weight in water from rainfall and develop a nasty case of mold as well.

Switchgrass is being evaluated by the University of Tennessee and others as a possible feedstock for cellulosic ethanol production. Cellulosic ethanol technology has not been commercialized and currently there is no commercial value outside of research for switchgrass production.

The evaluation looked at two methods of harvesting switchgrass — using a Massey Ferguson rectangular baler and a John Deere round baler. They produced a 5-foot by 4-foot round bale and a 4-foot by 8-foot rectangular bale. Quality and handling and storage costs were observed on pallets, on gravel on well-drained ground, and covered with either a plastic tarp, no tarp or wrapped in plastic.

According to Burt English, agricultural economist at the University of Tennessee, the bales went into storage on Jan. 25, just after harvest. “We would have liked to have harvested earlier because the sooner you harvest after the first frost, the better off you are.” English noted that the delay was due to a missed opportunity in getting a specially equipped rectangular baler to the site.

For the round baler, researchers assumed a 5-ton per hour harvest capacity, “which is a little on the low end of the designed capacity of some balers, at an initial cost of about $23,000.”

The rectangular baler capacity assumed a 12-ton per hour harvest capacity, which was also a bit low for its designed capacity. “We have a longer useful life for the rectangular baler, plus a larger tractor requirement than for the round baler.” The rectangular baler cost almost $88,000.

For staging and stacking, a bale spear moved one rectangular bale and two round bales at a time. Staging costs remain constant whether with round bales or rectangular bales.

Researchers found that for the round bale, there is very little cost difference between 100, 200 or 300 acres — at $17 per ton to harvest and stage. Harvest cost decline on the rectangular bale significantly to around $10 to $11 per ton at 300 acres, because the cost is spread over more acres.

Since an ethanol facility would presumably not require its cellulosic feedstock all at once, storage is crucial to bale quality, according to English. He added that researchers actually don’t know at this time if bales of switchgrass necessarily have to be covered, because quality standards for switchgrass haven’t been established.

English said stacked bales of switchgrass could be covered by a 25-foot by 100-foot tarp at a cost of $502. It would cover 144 rectangular bales or 120 round bales.

A producer will need 72 pallets at $6.50 each to store round bales and 96 pallets to store rectangular bales. A gravel storage pad will cost about 60 cents per square foot to build, amortized over five years. “If it lasts longer, that would reduce the cost. A pad for round bales will require 2,000 square feet of gravel, the rectangular, 1,900 square feet.

Two laborers to attach tarps and lay the pallets out will cost $9.75 per hour. There is also a charge for a pickup truck to haul the pallets and the tarps to the site.

Researchers used a chain saw to cut open the bales to evaluate the interior of the bales after 100, 200, 300, 400 and 500 days of storage. The covered round bales generally showed few signs of weathering, and bale weights decreased by an average of 37 pounds per bale, according to English.

Uncovered round bales showed weathering in the outside layer of the bale and had an average weight gain of 117 pounds per bale.

Weathering on the rectangular bales tarped on top occurred along the sides of the bale, with occasional weathering on the bottom of the bales. Average bale weight increased 113 pounds. Uncovered bales were soaked through, and the average weight of the bales increased by a whopping 1,360 pounds. “So instead of moving a 1,700-pound bale, we’re moving a 3,000-pound bale. Moving that much water if the plant doesn’t need it, doesn’t make sense.”

Mold was discovered in the uncovered rectangular bale as well, “but we don’t know if that’s bad or good.” English noted that samples of the bales have also been taken to determine if there is an impact of weathering on eventual ethanol yield.”

Final information on bale degradation and on bale quality will be provided to farmers and to ethanol processors “so they can properly price the product,” English said. “We also want evaluate tradeoffs and costs of storage.”


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