Quality and Variability of Commercial-Scale Short Rotation Willow Biomass Harvested Using a Single-Pass Cut-and-Chip Forage Harvester

Abstract

To date, most of the data on the characteristics of many short rotation woody crops has come from biomass that was hand harvested from small-scale yield trials. Concerns have been raised that there is insufficient information regarding the variability in biomass characteristics when material is harvested at commercial scales, which can impact the efficiency of biorefineries and other end users. The objectives of this study are to (1) characterize the biomass (i.e., ash, moisture, energy and elemental content, and particle size distribution) generated from commercial-scale shrub willow harvests at two sites, (2) evaluate compliance the published International Organization for Standardization (ISO) standards, and (3) contrast with “pristine” biomass from yield trials. Commercially generated chips were generally compliant with ISO standards for B1 chips. The mean ash content was 2.1 % (SD 0.59) dry basis and ranged from 0.8 to 3.5 % for samples collected from 224 truckloads of chips. There was a site effect for ash: 100 % compliance at one site and 82 % compliance at the second; loads exceeded the 3 % standard by less than 0.5 percentage points. The ash content of the Fish Creek cultivar was almost 1 % less than other cultivars and it is significantly lower (P < 0.0001). The mean moisture content was 44 % (SD 2.2) and ranged from 37 to 51 %. The harvested biomass was similar to pristine biomass with the exception of ash content, and the variability was similar across all characteristics measured. The low variability of willow biomass characteristics suggests that material with a consistent set of characteristics can be generated from willow crops with a cut-and-chip harvesting system.