Differential water and imidacloprid transport under unsaturated Florida citrus field conditions

Citrus production in Florida declined in the past 20 years by >72% due to citrus greening disease which is vectored by Asian citrus psyllid (ACP). Extensive use of pesticides such as imidacloprid (IDP) to manage ACP raises concerns of environmental pollution to shallow groundwater in citrus orchards dominated by sandy soils. We investigated water and IDP transport and its processes under saturated and unsaturated conditions using a combination of experimental data and advective−dispersive and Water and Agrochemicals in the Soil, Crop, and Vadose Environment (WAVE) models, respectively, to provide best management decisions for water and IDP movement in the citrus critical root zone (CCRZ). Monte Carlo and global multilevel coordinate search combined with Nelder−Mead Simplex methods were used for parameter optimization. The variance decomposition method was used to determine global sensitivity of the parameters. Mechanical dispersion and molecular diffusion processes equally influenced the movement of IDP at 0−30 cm, while mechanical dispersion predominantly governed IDP transport process at 30–60 cm under saturated conditions. Leaching of IDP beyond CCRZ was after a consistent and ≥4 h rain. Soil turbation following hurricane impacted soil water dynamics. Although field soil moisture content ( θ ) remained above field capacity, precipitation spike resulted in about 25% increase in θ . WAVE explained variation in θ time series with Nash–Sutcliffe efficiency ≥ 0.5 across soil depths and matched the IDP chemographs during the pesticide application periods. Global sensitivity analysis showed that saturated θ was the dominant factor controlling hydraulic response variation in the CCRZ.