Charcoal is a natural component of almost all soils, and when it is present in high concentrations it provides important benefits, increasing soils' ability to store water, and sometimes changing soil texture and soil biology in ways that are helpful for both agricultural and natural ecosystems.  Prior to this grant, little was understood about the physical mechanisms that allowed charcoal to provide helpful ecosystem services like soil water storage and soil carbon storage. Even without this information, many businesses and environmental groups were going forward with soil charcoal amendment (called biochar when made commercially and sustainably for intentional soil use).  Businesses, farmers, and environmentalists hope that biochar will improve soil performance and sequester carbon.

Prior to the work done in this grant, very large variations had been observed in soil hydrological properties when charcoal was added, with sometimes opposite results occurring in different soils, or with different charcoals.  The focus of this grant was the development of generalizable models to help better understand how charcoal acts to change soil properties, especially properties associated with water and carbon.

This research project focused on charcoal physical properties.  We were particularly interested in soil hydraulic conductivity (a measure of the rate at which water drains through soils), because this property plays such an important role in retaining water in soil in environments prone to drought, and conversely in removing water from landscapes prone to flooding.  We showed that charcoal amendment can both increase and decrease soil saturated hydraulic conductivity, with the direction of change dependent on the amending soil, the size of the charcoal particles, and the internal porosity of the charcoal particles.  Separately we characterized how charcoal internal porosity varies with production conditions (biomass source and pyrolysis temperature).  These results suggest that it will be possible for businesses to produce biochar in particle sizes and porosities targeted for specific needs, like helping farms survive drought and helping urban environments reduce flooding.

Two other physical properties that we studied were charcoal density and porosity, because the density and porosity of charcoal are key controllers of its landscape and hydrologic behavior. Density is important because materials with densities less than 1 g/cm3 are prone to floating and may be lost from soils to rivers after heavy rainfall.  Porosity (the percent of a sample’s volume that is open space) is important because charcoal's internal pores create space for water and microbes, and can sometimes act to divert and/or slow water flow through soils.  We showed that charcoals made from wood have porosities ranging from 55-85% (Brewer et al., 2014), and that charcoal density varies widely.

In this grant we accomplished the following:

1. Developed fast, cheap, safe techniques to measure charcoal density and porosity,

2. characterized these properties in the lab and in the field,

3. related them to saturated hydraulic conductivity and soil water potential, and

4. examined how they varied with environmental conditions.

We have collaborated with four local businesses and two energy companies during this project.

To date this proposal has resulted in 15 published papers, with 2 additional papers in review and 3 in preparation.

Brewer, C. E., Chuang, V. J., Masiello, C. A., Gonnermann, H., Gao, X., Dugan, B., et al. (2014). New approaches to measuring biochar density and porosity. Biomass and Bioenergy, 66(c), 176–185. http://doi.org/10.1016/j.biombioe.2014.03.059.

Last Modified: 12/31/2015
Modified by: Caroline A M...

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