Mobility of Fluopyram in soils under saturated flow conditions

A new generation of non-fumigant nematicides has recently been introduced and is essential to enable efficient and sustainable agricultural production. Fluopyram (FL) is a new compound with a novel mode of action and an improved safety profile. The aim of this study was to quantify the adsorption and transport of FL in 3 soils with different texture under increasing water flows. Initially, equilibrium adsorption isotherms were measured by batch method. Then, FL transport characteristics were analyzed by flowthrough experiments under saturated flow conditions in soil columns. A pulse input of FL was given together with Bromide (Br), used as a conservative tracer. The flowthrough experiments were performed with 3 different soil types, loamy sand, loam and clay under 3 water flow rates, 0.3, 1 and 4 ml min^-1, then analyzed and simulated with the convection–dispersion equation (CDE). Equilibrium and kinetic reaction terms were employed to consider sorption of FL. The adsorption isotherms of FL exhibited linear behavior for all soils, with distribution coefficient (K_d) varying from 0.72 to 1.87 L Kg^-1 for loam and clay respectively. The established breakthrough curves (BTCs) obtained for bromide exhibited a symmetrical pattern, regardless of soil texture and flow rates, with an average of 100% of Br recovered, suggesting that physical equilibrium is prevailing in all columns. The FL BTCs exhibited sharp increase in concentration after pulse input and long tailing during leaching phase, not fully completed after leaching for 17 pore volumes (PV). The experimental mass balance demonstrated a maximum of 90% recovery on sandy soil and a minimum of 79% in clayey texture. This might indicate that FL has fast adsorption on soil and slow desorption kinetics or even some irreversible adsorption. To understand better the processes affecting FL transport in soils, two models of solute transport were used, a Two-sites sorption model (TSM) and Two-kinetic sites model. When irreversibility was assumed, both models underestimated the tailing of BTCs, trending the curve to zero; showing that instead of irreversible desorption, the long-term leaching behavior is due to a very slow desorption rate. All the models could describe well the adsorption process and confirmed that part of FL has quick adsorption in soil which is in agreement with the low mobility observed. Further evaluation on FL transport characteristics and the adequacy of the different numerical model will be discussed.