Harvesting
Traditional hay harvesting of warm-season prairie grasses for winter forage usually occurs in late June or early July (varies by location). If harvested earlier, the hay would likely have greater protein and if later, higher yield. Later cutting reduces plant vigor and repeated over time will typically unfavorably alter stand composition. At this stage, the grass has a moisture content of 30 to 40 %. The grass is moved or swathed and allowed to dry until moisture content reaches 10 to 15 % before being baled into large round or square bales. Small bales are seldom used due to high labor costs. Using grass as a biomass energy resource requires a different strategy, with harvest beginning after fall frost and, subject to weather conditions, continuing through winter. Post-frost harvest has two important advantages: 1) grass moisture content will typically be <10 %, reducing the need for drying time and the risk of weather damage, and 2) the plant has become dormant and harvest has little impact on plant life. Efforts to use prairie grasses for biomass energy have thus far relied on traditional hay harvesting methods. Alternative methods might reduce costs and embodied energy. Possible scenarios include the following:
1) Integration of the swather and bailer into a single machine.
2) Use of a wide head forage harvester combined with truck or bin transport.
3) Pelleting in the field.
Adaptation of Forage Handling Systems for Collecting Biomass Feedstock.
S. Sokhansanj, Oak Ridge National Laboratory,
and L. O. Pordesimo and W. E. Hart, The University of Tennessee.
ABSTRACT
"Field experiences using existing forage handling equipment in biomass applications indicate that this equipment can be used for handling biomass, provided the equipment is reinforced and equipped with more power. Since stover and straw, crop residues available for utilization, are the mature stage of the plant material, they are tougher than green forage, especially alfalfa, the predominant forage crop. In some specific applications such as collecting corn stover, modifications are required to minimize contamination of material with soil. The nature and extent of modifications to existing machinery have not been quantified. Field data is needed to identify critical developments in machinery to handle large quantities of biomass for biorefineries of the future."