Switchgrass drying time shorter than traditional forages

Perennial grass dries quickly after cutting, ready to bale in a day.

Switchgrass is a high yielding bioenergy crop that is harvested with equipment that would be used for grass hay. In the fall, after the plant has matured and began to senesce, the crop is mowed with a discbine and baled. Anyone who has ever put up hay knows the later in fall you wait to cut, the harder it is to get your hay dry enough to bale. However, according to Michigan State University Extension, switchgrass has some unique characteristics that make drying time much shorter than many traditional types of forage.

First, switchgrass is considerably drier at harvest than typical forages at cutting time, according to “Harvest and Storage of Two Perennial Grasses and Biomass Feedstocks” by K.J. Shinners et al. This is one of the benefits of cutting a mature crop. Forage quality is much lower when waiting to harvest this late, but for bioenergy purposes, forage quality is much less important.

Second, the long, rigid stems and wide leaves help the switchgrass remain on top of the stubble, allowing better air flow beneath the swath. Alfalfa and other supple forages tend to settle down into the stubble, reducing airflow and lengthening dry time. Getting proper airflow under the swath will reduce dry time on any forage crop. Also, using 100 percent of the swath width improves dry time over a 60 percent and 30 percent swath width.

Conditioners are used to break the stems and help remove the waxy layer on the stem surface to improve dry time. In the study conducted by Shinners et al., no significant difference was observed between roll and impeller conditioners. It is important to note that forage crops should be conditioned such to maintain integrity of the leaves to improve forage quality. This is not an issue with switchgrass, so more aggressive conditioning will not hurt the crop as long as it is not chopped up and dropped on the ground where the baler can’t pick it up. However, in most cases, switchgrass yields are higher than traditional forages, resulting in more material going through a mower or conditioner at a time, which reduces the amount of conditioning as compared to lower volumes of throughput.

In my experience, switchgrass can be cut then baled 24-36 hours later if properly managed. Finding a window of opportunity where the weather cooperates can be a challenge, but not impossible. Two 80-acre fields near the Kellogg Biological Station in Hickory Corners, Mich., were harvested in 2010, 2011, 2012 and 2013 with bale moisture content of 16.2, 22.6, 15.8 and 21.5 percent, respectively. This was achieved with one day of dry time between cutting and baling. In 2011, the bales did get rained on before sampling occurred, thus the higher moisture content. In 2013, the yield ranged from 3-5 tons dry matter per acre in each field. This high amount of biomass increased dry time needed in the windrow. A discbine mower with a metal roll conditioner was used. Cutting height was 6 inches. Swath width was approximately 50 percent (7-foot wide swath from 14-foot head).

For questions or comments, please contact Dennis Pennington at pennin34@msu.edu or 269-838-8265.


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