Biochar alters hydraulic conductivity and impacts nutrient leaching in two agricultural soils

Journal Article · 21 December 2021 · Soil

DOI: https://doi.org/10.5194/soil-7-811-2021 · OSTI ID:1983344

Gelardi, Danielle L.  ^[1]; Ainuddin, Irfan H. ^[2]; Rippner, Devin A. ^[3]; Patiño, Janis E. ^[4]; Abou Najm, Majdi  ^[4]; Parikh, Sanjai J. ^[4]

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1. Univ. of California, Davis, CA (United States); Washington State Department of Agriculture, Olympia, WA (United States)
2. California State University, Chico, CA (United States)
3. US Dept. of Agriculture (USDA), Prosser, WA (United States). Horticulture Crops Research Unit
4. Univ. of California, Davis, CA (United States)

Biochar is purported to provide agricultural benefits when added to the soil, through changes in saturated hydraulic conductivity (K_sat) and increased nutrient retention through chemical or physical means. Despite increased interest and investigation, there remains uncertainty regarding the ability of biochar to deliver these agronomic benefits due to differences in biochar feedstock, production method, production temperature, and soil texture. In this project, a suite of experiments was carried out using biochars of diverse feedstocks and production temperatures, in order to determine the biochar parameters which may optimize agricultural benefits. Sorption experiments were performed with seven distinct biochars to determine sorption efficiencies for ammonium and nitrate. Only one biochar effectively retained nitrate, while all biochars bound ammonium. The three biochars with the highest binding capacities (produced from almond shell at 500 and 800 °C (AS500 and AS800) and softwood at 500 °C (SW500)) were chosen for column experiments. Biochars were amended to a sandy loam and a silt loam at 0 % and 2 % (w/w), and K_sat was measured. Biochars reduced K_sat in both soils by 64 %–80 %, with the exception of AS800, which increased K_sat by 98 % in the silt loam. Breakthrough curves for nitrate and ammonium, as well as leachate nutrient concentration, were also measured in the sandy loam columns. All biochars significantly decreased the quantity of ammonium in the leachate, by 22 % to 78 %, and slowed its movement through the soil profile. Ammonium retention was linked to high cation exchange capacity and a high oxygen-to-carbon ratio, indicating that the primary control of ammonium retention in biochar-amended soils is the chemical affinity between biochar surfaces and ammonium. Biochars had little to no effect on the timing of nitrate release, and only SW500 decreased total quantity, by 27 % to 36 %. The ability of biochar to retain nitrate may be linked to high micropore specific surface area, suggesting a physical entrapment rather than a chemical binding. Together, this work sheds new light on the combined chemical and physical means by which biochar may alter soils to impact nutrient leaching and hydraulic conductivity for agricultural production.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). Advanced Light Source (ALS)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 1983344
• Journal Information: Soil, Journal Name: Soil Journal Issue: 2 Vol. 7; ISSN 2199-398X
• Publisher: Copernicus Publications, EGUCopyright Statement
• Country of Publication: United States
• Language: English