Duputel M., Van Hoye F., Toucet Joële, Gerard F. (2013). Citrate adsorption can decrease soluble phosphate concentration in soil : experimental and modeling evidence. Applied Geochemistry, 39, p. 85-92. ISSN 0883-2927.
Titre du document
Citrate adsorption can decrease soluble phosphate concentration in soil : experimental and modeling evidence
Applied Geochemistry, 2013,
39, p. 85-92 ISSN 0883-2927
The adsorption/desorption of phosphate (PO4) on soil minerals is a major process regulating soluble phosphate concentrations (i.e. phosphorus availability) and ultimately PO4 bio-availability. Release of citrate by roots is widely recognized as an effective biological mechanism for increasing available phosphorus (P) in soil. However, interactions between citrate and PO4 are poorly understood and little investigated in soils. Using surface complexation modeling we recently predicted that citrate adsorption can decrease available P in soils depending mainly on soil type and on citrate, exchangeable calcium, and soil organic carbon concentrations. The most pronounced decrease was predicted in chromic cambisols. The intention of the present study was to verify the accuracy of our predictions against experimental data measured in a real chromic cambisol, and to improve our understanding of PO4-controlling processes through surface complexation modeling. The addition of a low to moderate citrate concentration (<50 mu M) effectively decreased available P. In contrast, a concentration of 100 mu M produced an increase of available P. The maximum decline of available P was observed at 20 mu M of citrate. The agreement between simulated and measured values of P availability and total dissolved Ca concentrations was excellent at a citrate concentration ranging from 0 to 50 mu M. Our model substantially underestimated the increase of available P measured at 100 mu M of citrate. This discrepancy showed the presence of another PO4-controlling process, which revealed to be the dissolution of P-containing minerals, most probably illite. This study confirmed that the release of citrate in soils and its subsequent adsorption onto minerals can produce the decrease of P availability. Such citrate-induced decreases of available P can be observed after addition of a relatively low concentration. The threshold concentration was 20 mu M in the chromic cambisol investigated here. This validation should have serious implications in the prospect of rhizosphere management for a better PO4 acquisition by plants through citrate release, as an adverse effect of citrate can be expected, depending on soil properties and citrate concentration. This study also further demonstrated the ability of surface complexation models to reproduce and predict dissolved concentrations of various ions in soil solutions as a function of environmental conditions.
