Sorption and Transport of Phosphorus and Nitrogen in Soils from Florida and Nigeria in a Mixture of Fertilizers and Pesticides.

Most studies on sorption and transport of plant nutrients and pesticides are conducted by studying the chemicals individually. In this study, we compared sorption and transport of some agro-chemicals both individually and in mixture. Phosphorus (P) sorption kinetics and equilibrium (SKE) were studied from a mixture (Mix#1) of pesticides (Atrazine, Imidacloprid and Imidacloprid-urea) and a tracer (Pentafluorobenzoic acid, PFBA), with fertilizer sources (NH₄NO₃ + KH₂PO₄ + KCl, 8 mM) as the supporting electrolyte. Mix#1 was prepared based on recommended application rates for fertilizers and pesticides in crop commodities common to Florida, such as citrus and sorghum. In addition, P sorption was studied using a conventional supporting electrolyte: 8 mM KCl (Mix#2). Surface soils from two soil series (Candler sand, and Immokalee fine sand) from subtropical Florida, and a Tulluwa upland series (TUP3), which is a soil collected from the crest of a topo-sequence from semi-arid northern Nigeria, were used in this study. The SKE data show that parameters for P determined from Mix#1 and Mix#2 are essentially equal. Results from P kinetics were fitted with the two-site kinetic model for the Candler sand and TUP3, while the Immokalee A horizon was best described by the one-site kinetic model. SKE parameters obtained in Mix#1 and Mix#2 were compared and also used to simulate P transport through soil columns of the three soils. Mix#1 was also applied as a pulse input in soil columns under steady state saturated flow. PFBA and NO₃^- breakthrough curves (BTCs) were described by the convective-dispersive model, while P BTCs was described by two-site nonequilibrium transport model. The study showed that SKE and P transport parameters determined with the conventional method and the fertilizer-pesticide mixture can be used to describe P sorption and transport in these soils.