Impact of biochar coated with magnesium (hydr)oxide on phosphorus leaching from organic and mineral soils

Abstract

Purpose Recent research suggests that Swedish organic arable soils have been under-recognized as a potential source of phosphorus (P) loading to water bodies. The aim of this study was to compare P losses through leaching from organic and highfertility mineral soils. In addition, the effectiveness of a magnesium-salt-coated biochar applied below the topsoil as a mitigation strategy for reducing P losses was evaluated. Materials and methods Phosphorus leaching was measured from four medium-to high-P arable soils, two Typic Haplosaprists (organic 1 and 2), a Typic Hapludalf (sand), and an unclassified loam textured soil (loam), in a 17-month field study utilizing 90cm-long lysimeters. A magnesium-salt-coated biochar was produced and characterized using X-ray powder diffraction (XPD), scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), and X-ray adsorption (XANES) spectroscopy, and its phosphate adsorption capacity was determined at laboratory scale. It was also applied as a 3-cm layer, 27 cm below the soil surface of the same lysimeters and examined as a mitigation measure to reduce P leaching. Results and discussion Total-P loads from the 17-month, unamended lysimeters were in the order of organic 2 (1.2 kg ha −1) > organic 1 (1.0 kg ha −1) > sand (0.3 kg ha −1) > loam (0.2 kg ha −1). Macropore flow, humic matter competition for sorption sites, and fewer sorption sites likely caused higher P losses from the organic soils. Analysis by XRD and SEM revealed magnesium was primarily deposited as periclase (MgO) on the biochar surface but hydrated to brucite (Mg(OH) 2) in water. The Langmuir maximum adsorption capacity (Q max) of the coated biochar was 65.4 mg P g −1. Lysimeters produced mixed results, with a 74% (P < 0.05), 51% (NS), and 30% (NS) reduction in phosphate-P from the organic 1, organic 2, and sand, respectively, while P leaching increased by 230% (NS) from the loam. Conclusions The findings of this study indicate that P leached from organic arable soils can be greater than from mineral soils, and therefore, these organic soils require further investigation into reducing their P losses. Metal-enriched biochar, applied as an adsorptive layer below the topsoil, has the potential to reduce P losses from medium-to high-P organic soils but appear to be less useful in mineral soils.

Agricultural Water Quality in Cold Climates: Processes, Drivers, Management Options, and Research Needs

“…They find that gypsum amendment is very effective in reducing P release under both cold and warm conditions, but biochar is not. In a field lysimeter study conducted in Sweden, however, Riddle et al (2019) showed that biochar coated with magnesium (hydr) oxide reduced P leaching in both organic and mineral soils. The contrasting biochar results of Dharmakeerthi et al (2019) and Riddle et al (2019) suggest the potential influence of climate and soil conditions and biochar type on P turnover.…”

Repurposing distillation waste biomass and low-value mineral resources through biochar-mineral-complex for sustainable production of high-value medicinal plants and soil quality improvement

“…The SSA of BMC was comparatively lower than a bamboo-based biochar-montmorillonite composite (156 m 2 g -1 ) (Viglasova et al, 2018), but higher than a municipal solid waste biochar-montmorillonite composite (6.51 m 2 g -1 ) (Ashiq et al, 2019). Riddle et al (2019) reported that the reduction of SSA in biochar-mineral composite compared to pristine biochar could be due to the coating of biochar with metal hydr(oxide)s (e.g., magnesium hydroxide).…”

Magnesium-Palm Kernel Shell Biochar Composite for Effective Methylene Blue Removal: Optimization via Response Surface Methodology

“…However, a few studies displayed different results where the surface area of Mg-PKS biochar composite is smaller than the PKS biochar due to the accumulation of Mg elements on the surface of biochar (Fang et al, 2014;Riddle et al, 2019). Mg-PKS biochar composite made from PKS displayed a relatively large surface area compared to other feedstocks such as corncob and wood chips, where at least numerous of them are below < 500 m 2 g -1 (Shen et al, 2018;Zhao et al, 2018).…”