The functional role of organic acid anions in soil has been intensively investigated, with special focus on (i) microbial respiration and soil carbon dynamics, (ii) nutrient solubilization or (iii) metal detoxification and reduction of plant metal uptake. Little is known about the interaction dynamics of organic acid anions with the soil matrix and the potential impact of adsorption and desorption processes on the functional significance of these effects. The aim of this study was to characterize experimentally the adsorption and desorption dynamics of organic acid anions in five agricultural soils differing in iron and aluminium oxide contents and using citrate as a model carboxylate. Results showed that both adsorption and desorption processes were fast in all soils, reaching a steady state within approximately 1 hour. However, for a given total soil citrate concentration (ct) the steady state was critically dependent on the starting conditions of the experiment, whether most of the citrate was initially present in solution (cl) or held on the solid phase (cs). Specifically, desorption-led processes resulted in significantly smaller steady-state solution concentrations than adsorption-led processes, indicating that hysteresis occurred. As it is not possible to distinguish between different adsorption and desorption pools in soil experimentally, a new dynamic hysteresis model that relies only on measured soil solution concentrations was developed. The model satisfactorily explained experimental data and was able to predict dynamic adsorption and desorption behaviour. To demonstrate its use, we applied the model to two relevant situations involving exudation and microbial degradation. The study highlighted the complex nature of citrate adsorption and desorption dynamics in soil. We conclude that existing models need to incorporate both temporal and hysteresis components to describe realistically the role and fate of organic acids in soil processes. © 2011 The Authors. Journal compilation © 2011 British Society of Soil Science.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledged KAUST grant number(s): KUKC1-013-04
Acknowledgements: This work was supported by the Vienna Science and Technology Fund (WWTF, Grant No MA07-008), the Austrian Science Fund (FWF, Grant No P20069) and the UK Biotechnology and Biological Sciences Research Council. K.C. Zygalakis was supported by Award No KUKC1-013-04, made by the King Abdullah University of Science and Technology (KAUST). Andrea Schnepf is a Hertha-Firnberg Research Fellow. Tiina Roose is a Royal Society University Research Fellow. We thank Professor Gerhard Adam for providing the laboratory facilities for radioisotope experiments and measurements.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.