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Shrub willow cultivars developed for bioenergy can produce four to five dry tons (8-10 green tons) of harvestable biomass per acre annually (harvested every three to four years) on a variety of sites. These willow cultivars have a wide geographic range (based primarily on climatic factors of temperature and precipitation) that extends across much of the eastern and central U.S. and into southern Canada. Site conditions within this range can impact willow yield, operations and profitability. Willow can be grown on a wide range of sites including marginal lands, but with potential tradeoffs in plant productivity and the level of operational challenges. Other considerations for willow site selection include the slope of the land, size and layout of the fields, accessibility, and proximity to the biomass end user.
Soil is an important factor for any crop. Shrub willow can be grown in a variety of soils, but some basic criteria must be met. Soils that do not meet these criteria will inhibit plant survival and growth, and can impact the use of agricultural equipment. Soil characteristics can change within and between fields on a farm, so analysis of the entire land area under consideration for willow is recommended.
Soil drainage classification can be poorly drained to moderately well drained. Soils that are very poorly drained are generally not suitable for willow in most cases, as very wet soil conditions can inhibit plant growth and cause operational difficulties. Excessively well drained soils are also not recommended because willow is vulnerable to drought.
Soil pH between 6.5 and 7.0 is optimal for nutrient uptake. Soils outside this range will limit the availability of phosphorous and other nutrients, but willow has been grown successfully on sites with soil pH 5.5-8.0. Soil pH can be adjusted to some degree by the use of amendments such as lime and sulfur.
Willow can be grown on marginal lands, but in general, as with most crops, higher quality soils will likely produce higher biomass yields with fewer inputs and fewer operational challenges. Marginal lands, by definition, have one or more biophysical characteristics that limits the productivity and economic viability of traditional annual crops on those lands. Willow is less affected than other crops by some of these limitations, such as wetter soils, but some site limitations may still reduce productivity and operational efficiency in willow plantings.
The land use history, soil tilth and overall condition of the site should be considered in the decision to plant willow. These baseline conditions dictate the work and investment necessary to properly prepare the soil for planting. Sites that have been idle, compacted, overgrown with brush, etc. will require more work and investment to be made suitable for planting (see fact sheet on site preparation). Some sites may also require rock-picking, removal of hedgerows, new access roads or other site improvements. Despite these challenges, marginal lands may be a feasible option for willow in some cases to make use of idle lands and fields that are generally too wet for other crops, if operational and plant productivity challenges can be overcome.
Transporting feedstock to an end user is often a large percentage of delivered biomass costs, around 20-25%. Fields should generally be located less than 50 miles (one-way) to the biomass end user. The logistics of trucking harvested biomass should be considered, such as site access, load limits, seasonal access roads, height restrictions, etc.
The size and layout of willow fields is also important. The minimum recommended field size is 25 acres, and the preferred project size (group of nearby fields) is 100 acres or more. Larger, rectangular-shaped fields enable longer continuous runs of machinery and higher efficiencies. When renting specialized machinery, fixed costs are reduced in larger projects by spreading the costs of machine transport and use across a larger number of acres. Headlands thirty feet wide or more must be maintained on both ends of the willow rows if using a forage harvester system, but other unplanted areas should be minimized in order to maximize crop production (see fact sheet on headlands and planted area). Slope of the land should be 10% or less.
Each site is unique and should be considered on an individual basis, but following these general guidelines for site assessment and selection can make willow plantings more productive, and make operations more efficient and profitable. Please contact us directly for more information and assistance with individual site assessments.
The Northeast Woody/Warm-season Biomass Consortium - NEWBio is supported by Agriculture and Food Research Initiative Competitive Grant no. 2012-68005-19703 from the USDA National Institute of Food and Agriculture.
Led by Penn State University, NEWBio includes partners from Cornell University, SUNY College of Environmental Science and Forestry, West Virginia University, Delaware State University, Ohio State University, Rutgers University, USDA’s Eastern Regional Research Center, and DOE’s Oak Ridge National Laboratory and Idaho National Laboratory.
This work was supported by the New York State Energy Research and Development Authority (NYSERDA), the US Department of Energy (USDOE) and the US Department of Agriculture National Institute of Food and Agriculture (USDA NIFA). No funding agencies, SUNY, nor any of their employees makes any warranty, express or implied, or assumes any legal responsibility for the completeness, accuracy, or usefulness of any information or process disclosed here.