If you have been driving in rural eastern Iowa and noticed a lot of choppers and wagons, you might have been seeing the UI Biomass Fuel Project Miscanthus harvest.
When to harvest?
Miscanthus is harvested at a “weird” time of year compared to other Iowa crops: it is harvested in late winter. The harvest date has a big impact on moisture content, which is a very important consideration in biomass crops. Miscanthus leaves maintain moisture longer than the stems. In temperate climates such as Iowa, most leaves have dropped by late winter/early spring due to plant senescence, and the stem moisture content will drop below 20% which is needed for stable storage[1]. Plant senescence allows the crop to fully recycle nutrients from the above ground material back to the rhizomes for storage and use the following season. Another advantage of winter/ early spring harvest is the availability of equipment and the ease of travel across the frozen fields. New miscanthus shoots will start emerging when soil temperatures reach 50 ℉ and harvest should be completed by this point in the spring without damaging the new crop.
Harvest methods
Silage Chopping: A silage harvester can harvest whole plant material after it dries down in the field (Figure 1). Chopped material is blown into carts or traditional trailers similar to corn silage harvesting. If a cart is used, a tractor trailer stationed at the edge of the field can transport the miscanthus to storage or directly to the plant for energy generation (Figure 2). Check out a harvester in action here.
Mowing and baling: Miscanthus can be baled into round (Figure 3) or square bales (Figure 4) similar to corn stalks. Travel and transport can be greatly improved with baling this high density crop. Videos of a mower and a baler can be found here.
Method considerations
Both of the mentioned methods have their tradeoffs, but it is important for the individual farmer to determine their specific needs. Chopped miscanthus can result in more material left in the field, and a low density material that requires additional storage space. On the plus side, chopped material may not require additional processing requirements for end use. A mower conditioner and baler require extra steps to prepare it for final use, but it is an effective option for high density bales that require less storage space.
[1] Greenhalf, C.E., D.J. Nowakowski, N. Yates, I. Shield, A.V. Bridgwater. (2013) The influence of harvest and storage on the properties of and fast pyrolysis products from Miscanthus x giganteus. Biomass & Bioenergy. 56. 247-259.