Effects of pH and cations on phosphate-molecules adsorption into hematite and on P forms in an Oxisol amended with lime and phosphogypsum

• Ano de defesa: 2020
• Autor(a) principal: Firmano, Ruan Francisco
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Calcário; Espectroscopia; Gesso; Gypsum; Latossolo; Lime; Long-term management; Manejo prolongado; Oxisol; Spectroscopy
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/11/11140/tde-13012021-161825/

Phosphorus (P) has intrigued scientists worldwide since its discovery in 1669. The remarkable adsorption of P in soils from intertropical regions, which mostly cover underdeveloped countries, has been continuously studied and makes management with this oxyanion challenging in cultivated areas. The overall objective was to investigate relationships among pH, calcium (Ca) and magnesium (Mg) in a molecular-scale, as well as among P, iron (Fe) and carbon (C) chemistry in soils at field-scale. The thesis begins in chapter two with a molecular-level study between the surface of minerals and phosphate molecules in the face of pH and cations (Ca and Mg) variations, mimicking what commonly occurs in acidic soils after the lime addition. The presence of Mg influenced the adsorption of myo-inositol hexakisphosphate (IHP6), which, like phosphate, exhibited two adsorption mechanisms. Kinetic parameters of IHP6 and inorganic phosphate adsorption were more influenced by pH than by the presence of cations in the colloidal systems. In the following three chapters, the indirect effects of prolonged management with aluminum (Al) suppressors, such as lime or phosphogypsum, are addressed in an Oxisol under no-till system. Chapter three explores the mineralogical and physicochemical properties of Fe forms, especially Fe-(hydr)oxides and phases associated with C. Lime broadcast apparently did not increase the association of Fe-oxides with organic C, but affected the potential adsorption of P in the soil. Crystalline Fe phases were affected by the prolonged use of lime and phosphogypsum, but the phases of lesser structural arrangement were found just in a native forest soil. In chapter four, an associative approach was made between spectroscopy and chemical fractionation techniques in order to clarify how inorganic forms of P (Pi) respond to the prolonged addition of these amendments. Most P species were associated with Fe-(hydr)oxides as hematite and goethite of varied structural orders. Sequential extractions were performed and high proportions of P associated with kaolinite were identified and correlated with residual P concentrations, which indicates storage of non-labile P forms in the phyllosilicate. Finally, in chapter five, the emphasis was on organic forms of P (Po) and their relationships with the activity of enzymes that mineralize P and C in the soil profile, as well as the yield performance of soybeans (Glycine max L.). There was a stratification of certain chemical attributes and enzymes in the soil, but the joint use of Al-suppressors increased the general availability of nutrients and soybean yields. The use of lime and/or phosphogypsum, however, did not promote an increase in Po identified by 31P nuclear magnetic resonance, composed mainly of IHP6.