Summary
This laboratory study investigates how added fulvic acid competes with native soil organic matter for binding sites on metal (hydr)oxide surfaces, and how this competition influences phosphate availability across a range of agricultural soils. Using surface complexation modelling, the authors demonstrate that fulvic acid adsorbs only to external nano-aggregate surfaces and that pH strongly modulates the competitive dynamics: at low pH, both added and native fulvic acid shift towards oxide surfaces, displacing phosphate; at higher pH, this competition weakens and phosphate remains more tightly bound. The findings have implications for organic amendment strategies, suggesting greater phosphate mobilisation potential in acidic soils, though with potential trade-offs for nutrient runoff.
UK applicability
The findings are relevant to UK arable and horticultural systems, particularly on naturally acidic soils common in upland regions where organic amendments are widely used. However, direct applicability depends on whether UK soils fall within the reactive surface area and pH ranges studied; the abstract does not specify the geographical origin of the soil samples or their representativeness to UK conditions.
Key measures
Fulvic acid adsorption; phosphate release; pH-dependent competitive adsorption; nano-aggregate size distribution; surface complexation model parameters (NOM-CD model)
Outcomes reported
The study measured adsorption of added fulvic acid and corresponding phosphate release across agricultural soils with varying properties using surface complexation modelling. It characterised organo-mineral nano-aggregate structures (10–270 nm) and quantified how pH affects the competition between fulvic acid and phosphate for binding sites on soil oxide surfaces.
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