Biochar alters hydraulic conductivity and impacts nutrient leaching in two agricultural soils
Author:
Gelardi Danielle L.ORCID, Ainuddin Irfan H., Rippner Devin A., Patiño Janis E., Abou Najm MajdiORCID, Parikh Sanjai J.
Abstract
Abstract. Biochar is purported to provide agricultural benefits when added
to the soil, through changes in saturated hydraulic conductivity (Ksat)
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 Ksat
was measured. Biochars reduced Ksat in both soils by 64 %–80 %, with
the exception of AS800, which increased Ksat 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.
Publisher
Copernicus GmbH
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