Agrochemical leaching reduction in biochar‐amended tropical soils of Belize.

The aim of this study was to determine the effects of biochar addition on agrochemical leaching in tropical soils of Belize. Biochars were produced from mixed softwood, rice husk and miscanthus straw, each pyrolysed at 700°C. Loam, sandy silt loam and clay loam tropical soils were amended with 0, 1, 2.5 and 5% (w/w) biochar to determine atrazine, diuron, enrofloxacine, oxytetracycline and tetracycline absorption in batch studies following OECD 106 guidelines. FOCUS groundwater modelling was performed with the results of the batch‐sorption study and alterations to the soil profiles to explore the effect of biochar amendment on the leaching of atrazine in a risk assessment context. Results showed that agrochemical sorption was higher in biochar‐amended soils than soils without biochar amendment. Soil organic matter content and biochar amendment contributed to the agrochemical sorption increase in soils. The FOCUS modelling showed a significant reduction in predicted environmental concentration in groundwater (PECgw) of atrazine when biochar was applied as a soil amendment. However, a trade‐off was identified between the sorptive capacity of the biochar and the changes in hydrology in the soil as a result of the biochar incorporation. The amendment of Belizean tropical soils with rice husk biochar was shown to be an effective method to reduce the leaching of the selected agrochemicals, although widespread implementation should be conducted carefully, taking account of the potential trade‐offs with biochar use identified in our modelling. Highlights: Biochar‐amended soil is a feasible method to increase sorption and reduce agrochemical leaching to groundwater.Environmental fate modelling demonstrated that 1% and 2.5% biochar amendment could reduce atrazine leaching in soil.Modelling identified a biochar performance trade‐off: altered soil hydrology could lead to greater leaching.Biochar implementation must account for trade‐offs identified to ensure the mitigation works in each circumstance. [ABSTRACT FROM AUTHOR]