Calibration of an Al-exchange model in acid soils

Aluminium toxicity is a major constraint for the culture of maize in acid soils. By the mineral uptake, the plant itself contributes to the soil acidification, especially as the nitrogen is taken up in ammoniacal form. This process modifies the composition of the rhizosphere by dissolution of the Al hydroxides. Aluminium in solution reacts with fixed Ca and Mg on the soils and the root walls. The dynamics of the chemical species in rhizosphere results from kinetics of exchange and dissolution, which are functions of the soil properties and the root action. These processes are simulated using a mechanistic model which takes into account the kinetics of the various reactions as well as the reactivity of the chemical species. The analysed soils came from Colombia (Oxisol), Cameroon (Oxisol) and Thailand (Ultisol). The plant was an Al-tolerant maize cultivar coming from Cameroon (Zea mays L. ATP Yellow). The top soils 0-20 cm and the maize roots were analysed in order to evaluate the parameters of the model, i.e. surface charge and intrinsic exchange constants. For the soils, the kinetic parameters of the Al hydroxides dissolution were also studied. A culture device made it possible to study the effect of the roots on a fine soil horizon (rhizosphere). The use of a polyamide mesh 0.2 µm allowed the separate analysis of roots and soil after culture. Fitting of the model required two types of exchange sites, one with permanent charge (soil), the other with variable charge (root and soil). The Al dissolution was fitted with kinetic constants as well as solubility constants of the hydroxides. The results obtained using the culture device showed that the roots release the protons, the Al hydroxides dissolve, Al replaces Ca on the exchanges sites, the Al and Ca concentrations increase in solution and Al content in roots increase. The state of the soil exchange complexes and the soil solutions can be correctly simulated. It appeared that Al concentration in solution near the root is a function of the soil type and the kinetic constants for Al dissolution. The model showed the importance of the Al dissolution kinetics in the dynamics of this element between the soil and the roots, i.e. its toxicity. In prospect, under Al saturation in solution compared to Gibbsite shows the interest of the study of the organic ligands in the processes of Al detoxification by the plants.

Bibliographic Details

Main Authors:	Calba, Henri, Cazevieille, Patrick, Firdaus, Jaillard, Benoît
Format:	conference_item biblioteca
Language:	eng
Published:	WCSS
Subjects:	P33 - Chimie et physique du sol, U10 - Informatique, mathématiques et statistiques, F61 - Physiologie végétale - Nutrition, Zea mays, sol acide, aluminium, dissolution, modèle de simulation, racine, échange d'ion, rhizosphère, http://aims.fao.org/aos/agrovoc/c_8504, http://aims.fao.org/aos/agrovoc/c_89, http://aims.fao.org/aos/agrovoc/c_317, http://aims.fao.org/aos/agrovoc/c_2335, http://aims.fao.org/aos/agrovoc/c_24242, http://aims.fao.org/aos/agrovoc/c_6651, http://aims.fao.org/aos/agrovoc/c_3933, http://aims.fao.org/aos/agrovoc/c_6569, http://aims.fao.org/aos/agrovoc/c_1767, http://aims.fao.org/aos/agrovoc/c_1229, http://aims.fao.org/aos/agrovoc/c_7701,
Online Access:	http://agritrop.cirad.fr/511343/
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