PHOSPHORUS RETENTION IN A VARIETY OF SOILS AMENDED WITH BIOCHAR OR FE-COATED BIOCHAR

The addition of a soil amendment like biochar, the by-product of thermal pyrolysis of a carbon-rich biomass, can help nutrient depleted soils retain important nutrients like phosphorus. Biochar has several potential uses including nutrient and water retention, waste management, and carbon sequestration. The transport of excess phosphorus through water sources can lead to accelerated eutrophication, increased nutrients in water bodies. Eutrophication leads to toxic algal blooms, decreased dissolved oxygen, and other water problems. According to commercially available BiocharNow, biochar can adsorb up to 99.9% of phosphorus from solution. Many studies on the release and retention of P in biochar amended soils have produced varying results. Showing that the soil conditions and biochar characteristics, including, feedstock and pyrolysis temperatures, determine the retention and adsorption rates of P. The goal of this study was to determine the effects of phosphorus retention when commercially available softwood BiocharNow or treated iron-coated softwood BiocharNow were added to various soils. In other studies, iron-coating biochar has been shown to increase P adsorption. Each biochar was added to soils to create mixtures that were 5% by weight. To create an isotherm, 2 g of soil/biochar mixture was combined with 20 ml of extractant solution made of 0.01M KCl with varying concentrations of P made from KH₂PO₄. There were 7 phosphorus concentrations ranging from 0 to 100 mg P/L. The samples mixed for 24 hours to equilibrate, were centrifuged, and filtered through 0.45 um filters before being analyzed by Murphy-Riley colorimetric and ICP. Overall, the addition of biochar to the soils increased P sorption seen by a decrease in P in solution. Higher phosphorus retention was seen in all soils types when biochar was added. The iron-coated biochar increased retention the most in sandy soil, which retained very little without a soil amendment. At high phosphorus concentrations, there was more adsorption. This study shows that biochar and engineered biochar have many potential uses that can improve water quality issues, including phosphorus retention in soils.