The impact of biochar surface properties on sand and on sandy loam regarding water repellency, water retention, and gas transmissivity
Date
2018
Authors
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Publisher
University of Delaware
Abstract
Biochar is a carbon-rich material produced from heating biomass in an anoxic environment and used as a soil amendment. Biochar amendment to soils has shown many added benefits. It can reduce greenhouse gas emissions, increase soil fertility, reduce stormwater runoff, enhance soil-microbial activities, and mitigate soil contamination. Furthermore, the carbon in biochar is environmentally recalcitrant and may persist in soils for hundreds to thousands of years, providing an alternative soil carbon sequestration strategy. ☐ Because of these recognized benefits, the interest in using biochar for soil reclamation and soil fertility enhancement has been rising over the past decade. This then requires a better understanding of the effects of biochar on soil properties to optimize their use. Delineating the influence of biochar on soil physical properties will facilitate modeling efforts and provide a strategy to expediently assess soil property changes in large-scale biochar applications. Therefore, experiments were conducted to elucidate the effects of biochar amendment to sand and sandy loam on water repellency, water retention, and gas transmissivity. ☐ In Chapter 2, the effects of biochar amendment on soil water repellency was investigated using poultry litter biochar (PLBC) in a series of experiments testing the existence, persistence, and the solubility of organics covering the PLBC surfaces. The hydrophobicity of PLBCs produced at pyrolysis temperatures ranging from 300-600°C was characterized by measuring the contact angle with deionized water. Results showed that the hydrophobicity of PLBC increased with increasing pyrolysis temperature. The biochars that were the most and the least hydrophobic were then tested to confirm the hypothesis that organic vapors condensed on biochar surfaces during pyrolysis caused biochar hydrophobicity. Furthermore, the chapter shows PLBC surface roughness contributed to a measurable contact angle that may impart hydrophobic characteristics to mixtures with sand at 2 – 5 % mass biochar amendment rates. ☐ The experiments discussed in Chapters 3 and 4 were then conducted using PLBC produced from 300°C and commercially available Soil Reef™ pinewood-derived biochar (SRBC). The biochars were rinsed, oven-dried, and sieved to ~0.545 mm to reduce the impact of organic vapor coatings on biochar particles that may complicate the results of water retention and gas transmissivity experiments. The effects of post-treated biochars (PLBC and SRBC) were then assessed on sand and sandy loam at variable saturation conditions to identify the mechanisms responsible for altering soil-water retention and gas transport. ☐ In Chapter 3, a predictive model, based on particle pore spaces (pores between the particles and pores within biochar) and adsorption onto particles, was developed and tested for the sand and sandy loam receiving 2 and 7% by mass of either PLBC or SRBC amendment. ☐ The last set of experiments in Chapter 4 evaluated the gas transport parameters, gas diffusivity (Dp/Do) and air-permeability (ka), of sand and sandy loam at variable saturated conditions with 7% by mass biochar amendment. Both biochars were post-treated PLBC and SRBC. Biochar increased gas diffusion in sandy loam, but not in sand. However, biochar did decrease air-permeability in both sand and sandy loam.
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Keywords
Applied sciences, Biochar, PLBC, Sandy loam