Develop a tool to evaluate the value of biochar
There are thousands of acres of abandoned mine sites on National Forests across the western USA. These sites have been disturbed by dredging for gold, drilling for oil or natural gas, or other mining activities. Restoring soil productivity to many of these sites has been difficult since many sites have no soil organic matter or fine soil particles (e.g., silts and clays). Both of these soil properties help retain water to ensure plant success during droughty periods.
In addition, there are large areas of the western United States which face land management challenges related to wildfire, insect and disease outbreaks, and invasive species. To effectively manage forestlands will require treatments that improve ecosystem resilience, minimize wildfire risk, and improve watershed conditions. Currently, forest restoration or rehabilitation treatments involve forest thinning and regeneration harvests that can produce 40-60 million dry metric tons of woody biomass per year. This material has been largely ignored in the past, but is now being considered as a valuable resource for both bioenergy and the byproduct of pyrolysis, biochar. Production of biochar, coupled with new national and international policies that promote large-scale biomass utilization, can lead to changes in how forest soils and stands are sustainably managed.
In the western USA, a majority of excess woody biomass generated during normal harvest activities (i.e., slash piles) can be used as feedstock for the sustainable production of biofuel and could result in the production of large quantities of the byproduct biochar. Biochar is biomass-derived black carbon (C) produced through the pyrolysis process and is analogous to black C naturally found in fire-prone ecosystems in the western United States.
Biochar has been used as a soil amendment in many agricultural systems and in addition to a long residence time for C sequestration, it can improve soil organic matter, nutrient cycling, and water holding capacity to enhance plant growth. Agricultural systems lend themselves to biochar application where it can be applied and incorporated during soil tillage operations, but abandoned mine lands, drilling pads, illegal roads, or other areas of forest ecosystems are also prime candidates for soil improvement from biochar additions.
Charcoal is a major component of the fire-prone ecosystems of the western USA as a result of wildfires or prescribed burns. Its composition is highly variable and the final product is a result of fuel type and moisture content, burn condition and duration, and ambient temperature. Past studies have shown increased water retention of biochar-amended agricultural soils.
Clear Creek Study Site — Umatilla National Forest
At the Clear Creek study site, dredging for gold created a soil matrix that is devoid of organic matter and silt or clay particles. On some sites, only cobbles are present on the soil surface, but on other sites a shallow topsoil layer had been applied. In both cases (cobbles or soil), plant mortality is high. Therefore, our study is using waste wood from slash piles that has been pyrolyzed and adding that charcoal (biochar) to the soil surface. On the site where only cobbles are present (Figure 1), we added biochar at various rates (none, 0, 2, 5, 10, and 20 tons/acre).
(Click on the first image below to go to slideshow view with full captions for each image.)
In addtion to the biochar rate study, we installed a second study site that will determine what type of soil amendment might be best for these types of soils and climate. We are using biochar, wood chips from a local mill, and biosolids from the Bend Waste Water Treatment facility. Biosolids have been tested to ensure they do not carry any diseases or heavy metals and are not placed close to the nearby stream. The biochar, chip, and biosolid treatments are used singly and in combination with each other. As with the rate study, native seed was planted and raked into the soil.
(Click on the upper left image below to go to slideshow view with full captions for each image.)
The main objective of both these study areas is to determine the best method(s) for restoring a thriving plant community with the ultimate goal of restoring forest vegation. We are monitoring soil temperature and moisture, nutrient leaching, and plant growth and will determine if waste wood from slash piles is a viable alternative for creating a usable soil amendment and then work to create markets where biochar can be sold.