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Repeated and long-term application of broiler litter (BL) to agricultural lands can lead to metal leaching into subsurface soil through preferential flow pathways, thereby raising concerns about groundwater quality. The application of BL along with biochar can provide sustainable solutions for agricultural and environmental management. Biochar, a carbon-rich material, can help reduce metal loss in runoff and mitigate metal leaching while enhancing soil quality and crop productivity. Thus, this study aims to quantify the impact of the BL application method (surface vs. subsurface) and investigate the effect of biochar on trace metal loss in leachate in a no-till pasture field dominated by preferential flow pathways located in Alabama, United States. Thus, 15 intact undisturbed soil cores were utilized for column-based successive rainfall simulation experiments. Different treatments consisted of surface and subsurface-banded applied BL, surface and subsurface-banded applied BL with Pinewood pristine biochar (BC), and a control with no BL and BC. Each treatment underwent three rainfall simulations conducted on the 0 th , 5 th , and 10 th days to understand metal leaching in consecutive drying-wetting scenarios. Breakthrough curves (BTCs) of bromide ions (Br‾) confirmed the presence of preferential flow in all soil columns. Metals, such as nickel (Ni) and chromium (Cr), were below the detection limits in leachate samples, whereas copper (Cu), zinc (Zn), aluminum (Al), and iron (Fe) were detected in significant concentrations. In control treatment, leachate samples recorded initial leaching of Cu (0.0002-0.005 mg L −1 ), Zn (0.03-0.04 mg L −1 ), Fe (0.02-0.07 mg L −1 ), and Al (0.19-0.51 mg L −1 ). In surface application of BL, treated columns leached more Cu (0.02-0.11 mg L −1 ) and Zn (0.03-0.12 mg L −1 ) due to soluble metals and changes in soil pH and dissolved organic matter, enhancing metal mobility compared to control columns. No significant difference in Cu and Zn leaching was found for BC application in surface and subsurface BL-applied soil columns. The Al and Fe concentrations in leachate for surface BL application ranged from 0.32 to 0.88 mg L −1 and 0.16 to 1.41 mg L −1 , respectively, which were higher compared to Al and Fe in subsurface BL applications, which ranged from 0.40-0.59 mg L −1 and 0.14-0.35 mg L −1 , respectively. Besides, Fe leaching from surface and subsurface applied BL-amended columns increased in consecutive drying-wetting over time, likely due to reducing conditions. Importantly, BC application leads to reduced Al and Fe leaching in both surface and subsurface-applied BL-amended columns. However, Al and Fe leaching was similar in BL-amended and control columns, as mostly Al and Fe were bound in immobile fractions in soil and BL. Moreover, with successive simulations, leaching of Cu, Zn, and Al decreased with and without BC application. This study demonstrated the practical feasibility of pristine BC, along with BL, in undisturbed soil, reducing metal leaching as a function of BC and BL application methods.
Brar et al. (Sat,) studied this question.