Dynamic effects of biochar concentration and particle size on hydraulic properties of sand

Authors: TRIFUNOVIC, BRANIMIR - Temple University; GONZALES, HOWELL - Temple University; RAVI, SUJITH - Temple University; Sharratt, Brenton; MOHANTY, SANJAY - University Of California

Submitted to: Land Degradation and Development
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/3/2018
Publication Date: 3/23/2018
Citation: Trifunovic, B., Gonzales, H., Ravi, S., Sharratt, B.S., Mohanty, S. 2018. Dynamic effects of biochar concentration and particle size on hydraulic properties of sand. Land Degradation and Development. 29:884–893. https://doi:10.1002/ldr.2906.
DOI: https://doi.org/10.1002/ldr.2906

Interpretive Summary: Biochar contains carbon and nutrients and as a soil amendment can enhance the function and quality of soils. In addition, biochar has the potential to alter soil physical properties and therefore wind erosion from agricultural lands. We found the size of biochar particles dramatically influences the hydraulic characteristics of a soil. Smaller biochar particles tended to clog soil pores, thus reducing the rate at which water moves through the soil but also increasing the amount of water held as the soil dries. These are desirable characteristics for both reclaiming lands that are sandy and for reducing wind erosion potential. Federal and state agencies responsible for conserving land resources (e.g. USDA-NRCS) as well as companies that manufacture biochar should promote the advantages of biochar in retaining soil water.

Technical Abstract: Large-scale application of biochar has been promoted as a strategy for reclaiming degraded soils and conserving natural landscapes because of biochar potentials to alter the soil biogeochemical and physical properties and improve soil quality. Several studies have reported that biochar amendment at different concentrations has inconsistent effect on soil hydraulic properties, but the cause of this inconsistency is not well understood. We hypothesized that biochar particle size would dynamically affect the water retention characteristic and can reliably predict the hydraulic conductivity of the amended soil. To test the hypothesis, we mixed Ottawa sand (a model geomedia) with a commercially available biochar by varying the concentration and size of biochar and measured their saturated (Ksat) and unsaturated hydraulic conductivity and soil water retention characteristics. Increases in the concentration of fine biochar (< 2 mm) consistently decreased Ksat; whereas increases in the concentration of unsieved or bulk biochar up to 5% (by weight) increased Ksat, and any further increases in biochar concentration decreased Ksat. Based on water retention curve of amended sand, the fine size fractions of biochar, and average pore size of sand, we attributed the change in Ksat to pore size alteration by added biochar particles. Biochar can either decrease (clog) or increase intra-particles pore space based on the quantity of fine biochar fraction, which appears to exert a primary control on the hydraulic conductivity of the amended sand. Thus, the soil conservation effort should consider biochar particle size, not just their concentration, as one operational control to maximize the intended benefits of biochar application.