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Sustainable Soils for Hardwood Biofuels

Nora Haider, Washington State University Extension

A graduate student is testing soil properties in a newly established poplar bioenergy farm.
A graduate student from the University of Idaho monitors soil at the newly established Pilchuck Demonstration Site.

Researchers want to know if bioenergy crops can be grown without degrading the environment and how poplars affect the soil compared to other crops and land uses. Understanding soil impacts will help determine the sustainability of new biomass feedstock systems.

To understand how the cultivation of hybrid poplar affects soil quality, the Sustainability Team is studying soils at poplar demonstration sites in Washington, Oregon, and Idaho. They are comparing soil properties of poplar sites to that of adjacent agricultural fields and forests. Field and lab measurements will determine how poplar cultivation affects physical, chemical, and biological properties of the soil.

“We are interested in how the soil changes in response to the changes in land use practices,” said Mark Coleman, Associate Professor at the University of Idaho College of Natural Resources. “We are especially interested in how the biological properties are changing at each of these sites.”

Understanding how much carbon is released versus stored in the soil during poplar production is an important aspect of how poplar-based biofuels may reduce greenhouse gases in the atmosphere. Researchers hope to gain insight into the relationship between poplars and soil by measuring changes in carbon and nitrogen concentrations, bulk density, and microorganism activity at various soil depths. In addition, researchers will measure greenhouse gas (carbon dioxide, methane, and nitrous oxide) exchanges at the soil surface. By measuring the activity of microorganisms in the soil, researchers can determine the amount of decomposition that is occurring, which influences greenhouse gas fluxes at the soil surface.  Poplars are expected to improve soil quality in part because the roots of fast growing trees store large amounts of carbon in the soil.

The close proximity of the Pilchuck Demonstration Site in Western Washington to a managed, mixed-conifer forest affords a unique opportunity for researchers to make soil property comparisons in a forested area.  Soil properties are also being compared to those in an adjacent hay

Determining how hybrid poplars affect soil is an important component of AHB sustainability research that will continue throughout the project.