Interaction of Organic Phosphorus With Clays Extracted From Oxisols

Abstract

In highly weathered soils, such as tropical soils, organic phosphorus (P) may decline together with total P and could be represented by a relatively lower amount of inositol phosphates compared with temperate soils. The aim of this work was to understand the abiotic processes leading to inositol phosphate retention in highly weathered soils. Sorption of myo-inositol hexakisphosphate and inorganic phosphate (Pi) on two clay fractions (A and B) extracted from Brazilian oxisols was studied, examining both the extent of P retention and surface property modifications induced by anion sorption. The two clays were characterized by a high amount of crystalline iron oxides and kaolinite. In clay A, gibbsite was also present, plus a higher amount of organic matter. The two clays presented a similar specific surface area, but clay A had a lower microporosity. The amount of Pi sorbed on the two clays was similar, reaching a plateau at about 1.35 2mol m j2 , whereas the amount of myo-inositol hexakisphosphate was higher on clay A, 0.67 2mol m j2 , than clay B, 0.49 2mol m j2 . The retention of both P forms on the two clays was linked to the large presence of crystalline Fe and Al oxides. Whereas Pi adsorbed on the external surfaces and diffused into micropores, myo-inositol hexakisphosphate likely adsorbed only on the external surfaces. The precipitation of Al and Fe myo-inositol hexakisphosphate was also limited because of the small amounts of soluble Al and Fe forms. All these phenomena may contribute to justify the relatively low accumulation of these organic P compounds found in some highly weathered soils. (Soil Science 2008;173:694-706)

Identification of inositol hexakisphosphate binding sites in soils by selective extraction and solution 31P NMR spectroscopy

“…Several studies have reported correlations between IP 6 and amorphous metal oxides in acidic soils (Anderson et al, 1974;Giaveno et al, 2008;McKercher and Anderson, 1968;Turner et al, 2003). In addition, IP 6 concentrations have been shown to fluctuate in parallel with changes in amorphous Al and Fe hydroxides during long-term pedogenesis .…”

Soil organic phosphorus in lowland tropical rain forests

“…), leading to their stabilization and protection from biological attack (Celi and Barberis 2007). However, there is evidence that inositol hexakisphosphate interacts relatively weakly with clay surfaces in strongly-weathered soils, due to a reduction in the number of phosphate groups involved in its stabilization on crystalline mineral surfaces (Giaveno et al 2008). Indeed, studies of soil chronosequences in New Zealand indicated that inositol phosphate concentrations decline in old, strongly-weathered soils in parallel with a reduction in the concentration of amorphous metal oxides (McDowell et al 2007;Turner et al 2007).…”

Cargas superficiais da fração argila de solos influenciadas pela vinhaça e fósforo

“…Os valores de PCZ encontrados neste trabalho para o LVdf e gibbsita corroboram aqueles propostos para materiais ricos em óxidos de ferro e de alumínio, que variam entre 7,8 e 9,5. 7 Giaveno et al 21 avaliaram o potencial zeta de hematita e gibbsita sintéticas e da fração argila de dois Latossolos do Mato Grosso do Sul sob diferentes ambientes, Cerrado nativo e pastagem. Para hematita, o potencial zeta variou de +30 mV em pH próximo de 3,0 até -20 mV em pH 11,0, alcançando o PCZ em pH 7,0.…”

“…34 A adsorção de fósforo afetou o potencial zeta da fração argila dos solos (Figura 1), corroborando estudos prévios, nos quais se verificou que a adsorção específica do ânion fosfato torna a superfí-cie carregada mais negativamente e também reduz o PCZ. 16,17,20,21 A adsorção de P tornou a superfície da fração argila de ambos os solos mais eletronegativa e reduziu seu PCZ, sendo essas alterações mais pronunciadas quando as amostras foram previamente tratadas com vinhaça. Para o LVdf, sem vinhaça, na menor concentração inicial de P (0,08 mM), observa-se uma redução do potencial zeta, alcançando o PCZ em 3,6 e apresentando uma carga líquida negativa acima desse valor.…”

“…Além de sua elevada adsorção, o P causa significativas mudanças nas cargas superficiais das partículas do solo, tornando-as mais eletronegativas e reduzindo o PCZ. 16,17,21 Tais alterações, além dos benefícios da adubação fosfatada, podem contribuir para o aumento da capacidade de troca de cátions no solo, 3 importante no manejo da fertilidade do solo e, também, influenciar o comportamento sortivo de metais pesados e pesticidas.22,23 Por outro lado, o aumento da carga líquida negativa dos coloides pode facilitar a dispersão das partículas do solo. …”