New Insight into the Influence of Biochar Particle Size and Aging in Soil Sorption of Fluometuron

Application of biochar to soil is considered a sustainable strategy to mitigate pesticide contamination due to its high sorption capacity. This ability depends on several physicochemical properties, including particle size. Thus, this study evaluated the influence of two particle size ranges (0.063–1 mm and 1–2 mm) on the sorption of the herbicide fluometuron (FM) by a commercial biochar (BC) and how this sorption was affected by biochar aging in soil for 12 and 30 months. In a soil with low FM sorption capacity, the addition of fresh BC (2% and 4%) increased the herbicide sorption similarly for both particle sizes. However, this sorption decreased with BC aging, with a greater reduction observed in the soil amended with the smaller BC particles (90% reduction) compared with the larger ones (48% reduction) at the 4% BC rate. The FM sorption on unamended soil was highly reversible, whereas desorption was strongly reduced in soil with fresh BC. In soil amended with smaller-sized BC, the desorption increased with aging, while no FM desorption occurred in soil amended with fresh or aged larger-sized BC. This different sorption–desorption behavior of FM in BC-amended soil depending on particle size and aging emphasizes the importance of considering these parameters, as the effectiveness of BC applied to soil may be compromised.