Phosphorus desorption from typical Oxisol clay components: effect of low weight organic anions

• Grant number: 12/17098-0
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: December 01, 2012
• End date: November 30, 2013
• Field of knowledge: Physical Sciences and Mathematics - Geosciences
• Principal Investigator: Marcelo Eduardo Alves
• Grantee: André Luis de Moraes Penteado
• Host Institution: Escola Superior de Agricultura Luiz de Queiroz (ESALQ). Universidade de São Paulo (USP). Piracicaba , SP, Brazil

Abstract

Phosphorus adsorption is more intense in tropical soils than in those of temperate regions. This difference can be ascribed mainly to the clay mineralogical composition of the first ones which comprises greater amounts of kaolinite, gibbsite, hematite and goethite than those found in the soils of north hemisphere. This mineralogical composition is usually found in the clay fraction of Oxisols, a class of deeply weathered soils spreaded over great part of Brazilian terrritory. Although the adsorption contributes to the phosphorus storage in the soil region explored by the plant roots, the aging of this retention and the precipitation of calcium, iron and aluminum phosphates contribute for the so-called fixation of this nutrient to the soil solid phase. Therefore, the decrease in the strenght of P adsorption could contribute to increase its plant availability. According to the literature some anions derived from the ionization of organic acids such as acetic, citric, formic, malic and oxalic contribute to reduce the amount of P adsorbed by minerals and so, at least in a temporary way, to retard the more intense P retention that take place in tropical soils. In this context, the present research aims to evaluate if, besides the well-known decreasing effect on P adsorption, the coadsoprtion of organic anions also weaken the phosphorus retention by the minerals kaolinite, gibbsite, hematite, and goethite. For this, studies will be carried out about the individual effects of the anions acetate, citrate, formate, malate and oxalate on the kinetics desorption of a same P amount adsorbed on each above-mentioned mineral considering that to a faster desorption can be associated a greater weakening organic anion effect on the P retention.