Biomass Harvesting of High-Yield Low-Moisture Switchgrass: Equipment Performance and Moisture Relations

Abstract

Commercial hay and forage equipment was tested for biomass harvesting of high-yield, low-moisture switchgrass for overall suitability, mass throughput rate, and effects on switchgrass drying at a southeast U.S. location. Equipment included disc mower, mower conditioner, tedder, rotary rake, round baler, and forage harvester operated in switchgrass yielding up to 12.4 Mg DM/ha. A one-cut annual switchgrass harvest during winter was investigated for equipment handling of voluminous, light (dry) material. A first of two-cut harvest during summer was investigated for in-field switchgrass drying. Equipment throughput rate was presented for different losses, since machinery performance reporting is not fully standardized on the basis of productivity losses. Results showed that a disc mower equipped with a safety curtain became plugged with switchgrass from a one-cut harvest due to reduced clearance to material flow created by the curtain support. The mower conditioner operated in straight-standing, one-cut switchgrass at speeds up to 16.4 km/h and throughput rate up to 57 Mg DM/h. However, in extremely lodged switchgrass, the mower conditioner had to be operated at reduced speeds to minimize plugging. The pto-powered rotary rake handled the dry voluminous material well. The round baler performed at a maximum throughput rate of 48 Mg DM/h at 14.0 km/h. Throughput rates measured for mower conditioner and round baler were greater than previously reported, even when considering different productivity losses. The round baler equipped with a MegaWide Plus pickup did not limit baler performance as previously reported for other pickups. However, baler limitations were noted for switchgrass stems not aligned with the pickup, hitch entanglement with voluminous windrows, and collection of late season broken fines at critical baler locations. Mean round bale density ranged from 136 kg DM/m3 for the first of two-cut harvest in the summer to 168 kg DM/m3 for one-cut harvest in the winter. Maximum bale density was 173 kg DM/m3 for net-wrapped one-cut harvest. Mean bale density of twined bales was significantly less (p=0.05) than bale density for net-wrapped bales for the one-cut harvest. The forage harvester operated without problem at 3.2 km/h and produced particle geometric mean dimensions of 15.3 mm for the first of two-cut harvest in the summer compared to 8.5 mm for the one-cut harvest in the winter for the same theoretical length of cut. The mower-conditioner and tedder harvest treatment promoted rapid switchgrass drying from 67% to 18% moisture content (wet basis) within 48 h after cutting. The mowed and tedded treatment reached 23% moisture content in 188 h. The Rotz drying model predicted moisture contents that fell between the mower and mower-conditioner treatments for elapsed times up to 72 h after cutting, but the model response to tedding and precipitation resulted in increased differences between predicted and actual values. Overall, current hay and forage harvest equipment have improved capacity, but high-yielding voluminous, light switchgrass exposed equipment limitations.