Advances in shrub-willow crops for bioenergy, renewable products, and environmental benefits

Short-rotation coppice systems like shrub willow are projected to be an important source of biomass in the United States for the production of bioenergy, biofuels, and renewable bio-based products, with the potential for auxiliary environmental benefits and multifunctional systems. Almost three decades of research has focused on the development of shrub willow crops for biomass and ecosystem services. The current expansion of willow in New York State (about 500 ha) for the production of renewable power and heat has been possible because of incentive programs offered by the federal government, commitments by end users, the development of reliable harvesting systems, and extension services offered to growers. Improvements in the economics of the system are expected as willow production expands further, which should help lower establishment costs, enhance crop management options and increase efficiencies in harvesting and logistics. Deploying willow in multifunctional value-added systems provides opportunities for both potential producers and end users to learn about the system and the quality of the biomass feedstock, which in turn will help overcome barriers to expansion

Evaluation of a Single-Pass, Cut and Chip Harvest System on Commercial-Scale, Short-Rotation Shrub Willow Biomass Crops

Harvesting is the single largest cost in the production of short rotation woody crops (SRWC) like shrub 8 willow and previous systems tested in North America have not been effective for the size of material grown. The 9 objective of this study was to evaluate the performance of a single-pass, cut and chip harvester in conjunction with 10 two locally-sourced chip collection systems on 54 ha of coppiced willow harvests in New York State. Harvesting 11 and collection equipment was tracked for 153 loads over 10 days of harvesting using GPS dataloggers. Effective 12 material capacities (Cm) increased linearly with standing biomass up to 40 to 45 Mgwet ha-1 because ground speed 13 was limited by ground conditions. This relationship changed dramatically with standing biomass in the 40 – 90 14 Mgwet ha-1 range, where Cm plateaued between 70 and 90 Mgwet hr-1 and was limited by crop conditions and 15 harvester capacity. The relationship between standing biomass and the harvester’s Cm will probably change under 16 different crop and ground conditions. The size of the harvester and the experience of the operator are other factors. 17 This nonlinear relationship will impact cost and optimization modeling SRWC systems. Improperly sized headland 18 and long haul distances impeded the performance of locally sourced collection systems resulting in a 33% decrease 19 in Cm from the field to the headlands, and 66% from the field to short-term storage as biomass moves through the 20 system

Research Summary: Characteristics of Willow Biomass Chips Produced Using a Single-Pass Cut-and-Chip Harvester

Biomass for bioenergy and/or bioproducts can be sourced from forests, agricultural crops, various residue streams, and dedicated woody or herbaceous bioenergy crops. Despite this wide spectrum of promising feedstocks, no single biomass source can meet the projected demand, or is clearly superior to alternatives in all aspects of cost, quality, and acceptance

Overhead Protection Increases Fuel Quality and Natural Drying of Leaf-On Woody Biomass Storage Piles

Short-rotation woody crops (SRWC) have the potential to make substantial contributions to the supply of biomass feedstock for the production of biofuels and bioproducts. This study evaluated changes in the fuel quality (moisture, ash, and heating value) of stored spring harvested shrub willow (Salix spp.) and hybrid poplar (Populus spp.) chips with respect to pile protection treatments, location within the storage piles, and length of storage. Leaf-on willow and poplar were harvested in the spring, and wood chips and foliage with moisture content in the range of 42.1% to 49.9% (w.b.) were stored in piles for five months, from May to October 2016. Three protection treatments were randomly assigned to the piles. The control treatment had no cover (NC), so piles were exposed to direct solar radiation and rainfall. The second treatment had a canopy (C) installed above the piles to limit direct rainfall. The final treatment had a canopy plus a dome aeration system (CD) installed over the piles. Covering piles reduced and maintained the low moisture content in wood chip piles. Within 30 days of establishment, the moisture content in the core of the C pile decreased to less than 30%, and was maintained between 24%–26% until the end of the storage period. Conversely, the moisture content in the NC piles decreased in the first two months, but then increased to the original moisture content in the core (>45 cm deep) and up to 70% of the original moisture content in the shell (<45 cm deep). For all the treatments in the tested conditions, the core material dried faster than the shell material. The higher heating value (HHV) across all the treatments increased slightly from 18.31 ± 0.06 MJ/kg at harvest to 18.76 ± 0.21 MJ/kg at the end of the storage period. The lower heating value (LHV) increased by about 50% in the C and CD piles by the end of the storage period. However, in the NC piles, the LHV decreased by 3% in the core and 52% in the shell. Leaf-on SRWC biomass stored in piles created in late spring under climatic conditions in central and northern New York showed differing moisture contents when stored for over 60–90 days. Overhead protection could be used to preserve or improve the fuel quality in terms of the moisture content and heating value if more than two months of storage are required. However, the implementation of such management practice will depend on whether the end users are willing to pay a higher price for dryer biomass and biomass with a higher LHV

Research Summary: Development of a Single-Pass Cut-and-Chip Harvesting System for Short Rotation Woody Crops

Many types of specialized machinery for harvesting short rotation woody crops (SRWC) exist, including small and large single-pass cut-and-chip systems, whole stem harvesters, and baling systems. However, due to the limited scale of SRWC deployment, evolving technology, different operational scales, and management objectives, there is presently no dominant harvesting system in use. In New York State, several existing or modified harvesting platforms for SRWC from Europe and North America have been evaluated since 2001 for use in short rotation willow. Technical hurdles encountered on various harvesters that were tested during that time include the durability of equipment, low production rates, irregular feeding of stems into the harvester, limits on maximum stem sizes, and inconsistent size and quality of chips

Growing Season Harvests of Shrub Willow (Salix spp.) Have Higher Nutrient Removals and Lower Yields Compared to Dormant-Season Harvests

The commercial establishment of shrub willow (Salix spp.) biomass crops with three- or four-year harvest cycles raises concerns about nutrient removal (NR). In addition, leaf-on harvests outside of the typical harvesting window are becoming more prevalent with a changing climate, and require a better understanding of the potential impact of these changes on biomass production and NR. This study examined the time of harvest effects for six harvest dates on the nutrient and biomass removal of four shrub willow cultivars in central New York State. There were significant differences in biomass in the first-rotation harvest; yields ranged between 77 and 85 Mg ha−1 for the time of harvest treatments during the growing season, and between 93 and 104 Mg ha−1 after dormancy. Harvest timing had significant effects on N and K removal in the combined wood and foliar biomass. Willow harvested in October removed comparatively higher amounts of N (77.1 kg ha−1 year−1) and P (11.2 kg ha−1 year−1) than other harvests. Potassium removal was greater for plants harvested in June (51.2 kg ha−1 year−1) and August (52.5 kg ha−1 year−1). Harvest timing and cultivar interactions suggest that targeted cultivar selection and deployment could maintain yields and limit excess nutrient losses

Bulk Density Data of Willow Chips for Collection Vehicles Operating in a Short Rotation Willow Crop

Bulk density of willow chips collected using three methods described in accompanying paper

Integrated Stochastic Life Cycle Assessment and Techno-Economic Analysis for Shrub Willow Production in the Northeastern United States

The refereed literature contains few studies that analyze life cycle assessment (LCA) and techno-economic analysis (TEA) methodologies together for lignocellulosic bioenergy systems, using a stochastic modeling approach. This study seeks to address this gap by developing an integrated framework to quantify the environmental and financial impacts of producing and delivering shrub willow in the Northeastern United States. This study analyses four different scenarios from a combination of two different initial land cover types (grassland, cropland) prior to willow establishment, and two harvesting conditions (leaf-on, leaf-off). Monte Carlo simulations were performed to quantify the uncertainty of the results based on a range of financial, logistical, and biophysical variable input parameters (e.g., land rental rates, transportation distance, biomass yield, etc.). Growing willow biomass on croplands resulted in net negative GHG emissions for both leaf on and leaf off scenarios for the baseline. The GHG emissions were lowest for the leaf-off harvest on cropland (−172.50 kg CO2eq Mg−1); this scenario also had the lowest MSP ($76.41 Mg−1). The baseline grassland scenario with leaf-on harvest, results in the highest net GHG emissions (44.83 kg CO2eq Mg−1) and greatest MSP ($92.97 Mg−1). The results of this analysis provide the bioenergy field and other interested stakeholders with both environmental and financial trade-offs of willow biomass to permit informed decisions about the future expansion of willow fields in the landscape, which have the potential to contribute to GHG reduction targets and conversion into fuels, energy, or bioproducts for carbon sequestration and financial benefits

Development and Deployment of a Short Rotation Woody Crops Harvesting System Based on a Case New Holland Forage Harvester and SRC Woody Crop Header

Biomass for bioproducts and bioenergy can be sourced from forests, agricultural crops, various residue streams, and dedicated woody or herbaceous crops (USDOE 2011). Woody biomass feedstocks have advantages in the northeastern US where forests occupy 67.4% of the land area (Smith et al. 2007), agricultural production has been in a 20-year decline, and agricultural crop residues are in limited supply because of the high demand for herbaceous forage by the dairy industry. Woody biomass is available year-round from multiple sources, so end users are not dependent on a single source of material or a narrow harvest window; this ensures a year-round feedstock supply, reduces the risk of dramatic price fluctuations, and eliminates the need for complicated and expensive long-term storage of material, which has the added benefit of preserving the quality attributes of the feedstock. As perennial cropping systems, both natural forests and short rotation woody crops (SRWC), like willow (Salix spp.) and hybrid poplar (Populus spp.), produce environmental and rural economic development benefits beyond a renewable source of biomass