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

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.

Role of Rice Husk Biochar in Improving Soil Physical Properties of ex Gold-Mined Soil

“…Compared to without biochar application (0 Mg ha -1 ), the soil hydraulic conductivity decreased by 56-68 % as the biochar was applied up to 20 t ha -1 . It was also found by Gelardi et al (2021) that biochar decreased soil hydraulic conductivity by 64-80% in sandy and silt loam soils.…”

“…Another amendment material that is quite popular lately is biochar. Biochar could improve soil chemical properties (Yulnafatmawita et al 2020;Ethik et al 2021;Solfianti 2021), soil biological properties (Dermiyati et al, 2017;Nurbaity et al, 2019), and soil physical properties (Yulnafatmawita et al, 2021;Prakongkep et al, 2021;Gelardi et al, 2021;Fu et al, 2021).…”

Biochar influences soil health but not yield in 3‐year processing tomato field trials

“…Comprehensive characterization details were first reported in Gelardi et al. (2021). Unless otherwise stated, biochars were sieved to 2 mm and characterized using procedures recommended by the International Biochar Initiative (IBI) (2015).…”

“…Biochar‐filled trenches were immediately closed, burying the concentrated biochar at the center of each bed (Figure S1). This application technique was chosen to minimize wind erosion risk (Blackwell et al., 2010; Gelardi et al., 2021) and to collocate biochars with irrigation, fertigation, and the plant rhizosphere (Li et al., 2020). Furthermore, this technique simulates a high application rate in the rooting zone (4.56 t ha −1 applied in a band to approximately 10% of the field corresponds to a broadcast application rate of 45.6 t ha −1 ) while using less biochar in the bulk soil, reducing grower costs.…”

Unveiling nutrient flow-mediated stress in plant roots using an on-chip phytofluidic device

“…The chosen window of flow rates complies with the physically permissible range typically considered in this paradigm. [57][58][59] For each flow rate, the flow direction was maintained in the positive direction of the root growth (towards the channel outlet). An additional no-flow condition was maintained as a control for each flow rate configuration.…”