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ARS Home » Midwest Area » St. Paul, Minnesota » Soil and Water Management Research » Research » Publications at this Location » Publication #331942
Title: Influence of biochar particle size and shape on soil hydraulic properties

Author
item LIM, TAE-JUN - Rural Development Administration - Korea
item Spokas, Kurt
item Feyereisen, Gary
item Weis, Rena
item KOSKINEN, WILLIAM - Retired ARS Employee

Submitted to: Journal of Environmental Science and Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/3/2016
Publication Date: 8/17/2017
Citation: Lim, T., Spokas, K.A., Feyereisen, G.W., Weis, R.D., Koskinen, W. 2017. Influence of biochar particle size and shape on soil hydraulic properties. Journal of Environmental Science and Engineering. 5(1):8-15.
DOI: https://doi.org/10.12974/2311-8741.2017.05.01.2

Interpretive Summary: Different physical and chemical properties of biochar, which is made out of a variety of biomass materials, can impact water movement through amended soil. The objective of this research was to develop a decision support tool evaluating the impact of the shape and the size distribution of biochar on soil saturated hydraulic conductivity (Ksat). Plastic beads of different size and shape were compared with biochar pieces to assess impacts on soil water movement. Beads and biochars were added at the rate of 5% (v/w) to a coarse sand. Overall, the particle size of both beads and biochar had an effect on the water movement. Larger and smaller particle sizes than the original sand grains (0.5 mm) decreasing the water transport rate. Adding similar sized beads or biochar as the sand grains had no impact on water transport. The shape also influenced soil hydraulic properties, but only when the particle size was between 3-6 mm (˜10x the size of the coarse sand). Biochar particle porosity (internal pores) had no significant influence on the saturated water movement due to their small size and increased paths compared to the voids between particles. These results support the conclusion that both particle size and shape of the biochar amendment will impact the hydraulic properties, but the internal biochar porosity has very little impact on the water transport characteristics. These results are significant to farmers and policy makers and will assist scientists and engineers in developing improved models for assessing the impact of biochar additions on the soil system.

Technical Abstract: Different physical and chemical properties of biochar, which is made out of a variety of biomass materials, can impact water movement through amended soil. The objective of this research was to develop a decision support tool evaluating the impact of the shape and the size distribution of biochar on soil saturated hydraulic conductivity (Ksat). Plastic beads of different size and morphology were compared with biochar to assess impacts on soil Ksat. Bead and biochar at the rate of were 5% (v/w) were added to a coarse sand. The particle size of bead and biochar had an effect on the Ksat, with larger and smaller particle sizes than the original sand grains (0.5 mm) decreasing the Ksat value. The equivalent size bead or biochar to the sand grains had no impact on Ksat. The amendment shape also influenced soil hydraulic properties, but only when the particle size was between 3-6 mm. Intra-particle porosity had no significant influence on the Ksat due to its small pore size and increased tortuosity compared to the inter-particle spaces (macro-porosity). The results support the conclusion that both particle size and shape of the biochar amendment will impact the Ksat value.