Abstract
Context Ferralsols, which cover approximately 6% of the Earth’s continental surface, have unique phosphorus (P) retention properties.Aims The research investigates P adsorption properties under non-controlled conditions on lateritic soil samples, combining different methodological approaches.Methods Ferralsol samples were analysed using (1) adsorption kinetics and capacities (wet chemical experiment methods), (2) scanning electron microscopy (SEM) and transmission electron microscopy and (3) attenuated transmission reflectance-Fourier transform infrared spectroscopy (ATR-FTIR).Key results Wet chemical experiments accord with previous studies on lateritic soils where chemisorption mechanisms govern P adsorption. Further, P adsorption appears to affect soil particles’ structural stability and release of iron (Fe) species in solution. SEM mapping confirmed the location of P compounds in Fe-rich areas. ATR-FTIR identified two inner-sphere complexes: monodentate (FeO)PO2(OH) and bidentate (FeO)2PO(OH) at wavenumber positions 958±5, 1042±5 and 1095±8cm−1; and 930±5, 983±10, 1005±5 and 1122±9cm−1, respectively. Also, a band centred at 1030±4cm−1 suggested evidence of ternary complexes for P concentrations above 500mgP/L. Combined methods suggested the potential involvement of redox mechanisms and other ionic species in the formation and types of phosphate surface complexes.Conclusions Our approach builds on previous work in this field by showing evidence of complex ionic interactions governing P retention on lateritic soils. Novel insights are evidence of fluctuations in physical and chemical factors with phosphate adsorption and suggestion of inner-sphere and ternary surface complexation mechanisms.Implications Given the wide global distribution of lateritic Ferralsols, our findings have important implications for key emerging challenges relating to P cycling for crop production and environmental impact.
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