Unraveling clothianidin sorption in tropical agricultural soils enriched with rice straw-based farmyard manure

The widespread use of clothianidin as a pest control agent has led to its contamination in soil and water environments. We conducted an adsorption–desorption study of clothianidin in two different agricultural soils, namely Delhi and Manipur soils, with and without rice straw-based FYM amendments at 0.1, 0.2, 0.5, 1, and 2 μg/ml by using the batch equilibrium method. The results demonstrated that the equilibrium adsorption data conformed well to the Freundlich isotherm model (1/ n < 1), with R 2 values above 0.98 and standard error of estimation (SEE) below 0.60. Additionally, the pseudo-first-order kinetics model provided the best fit for the adsorption of rice straw-based FYM, exhibiting correlation coefficients (R 2 ) greater than or equal to 0.986 and SEE values of 0.41 or higher. Among the tested soils, Manipur soil amended with rice straw-based FYM (59.38–60.55%) exhibited the highest clothianidin adsorption capacity, followed by Delhi soil with rice straw-based FYM (54.75–55.28%), Manipur soil (52.53–53.26%), and Delhi soil (46.26–49.37%). Moreover, artificial neural networks (ANNs) also confirmed the importance of organic carbon and clay content through the adsorption coefficient (Kd) model. Characterization of the FYM using Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS) revealed N-H stretching of aliphatic primary amine and heterogenous surface properties with calcium abundance. The findings indicate that the addition of farmyard manure (FYM) enhanced the adsorption capacity of the soil containing higher organic carbon and clay content, with significant influence of primary amine and heterogeneous surface interactions.