Sorption, leaching, and degradation of dicamba in two Brazilian soils: A study into soil layers

Abstract

Understanding the behavior in soil of soluble and mobile herbicides, such as dicamba, is essential for efficient weed management. Thus, the objective of the research was to understand the sorption, leaching and degradation processes of dicamba along the profile of two Brazilian soils (Oxisol and Ultisol). The Oxisol collected is a very deep soil, the A horizon was collected in a layer of 0.10 m deep, the B horizon 2.0 m and the C horizon ranging from 5.0 to 6.0 m. In contrast, the Ultisol presents a difference between the most superficial horizons, the A horizon was collected at a depth of 0.10 m, the B horizon at around 1.0 m depth and the C horizon at a depth of 2.0–3.0 m. A High-Performance Liquid Chromatography (HPLC) was used to determine the herbicide in the soil solution. The Freundlich sorption coefficient (Kf) values of dicamba ranged from 0.53 to 0.88 mg (1-1/n) L1/n kg−1 in Oxisol and 0.25–0.69 mg (1-1/n) L1/n kg−1 in Ultisol, indicating a low sorption capacity of the herbicide in all profiles. The dicamba mobility index was higher in the Ultisol, ranging from 4.22 to 65.8 compared to the Oxisol, which ranged from 0.46 to 8.10. The degradation half-life time (DT50) of dicamba was short (∼4 days) in the A horizon of both soils compared to the other horizons. Moreover, persistence in the B and C horizons was higher in Oxisol (182 and > 250 days) compared to Ultisol (85.6 and 52.1 days, respectively). The sorption and mobility index of dicamba showed a correlation with soil pH and DT50 values, depending on the organic matter (OM) content. The recommendation of use of dicamba should consider the physical and chemical attributes of the soil as an alternative to reduce the risk of environmental contamination.