Spectroscopic techniques to evaluate phosphorus species in an Oxisol and soil minerals

• Grant number: 19/01213-4
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate
• Start date: May 24, 2019
• End date: March 27, 2020
• Field of knowledge: Agronomical Sciences - Agronomy - Soil Science
• Principal Investigator: Luís Reynaldo Ferracciú Alleoni
• Grantee: Ruan Francisco Firmano
• Supervisor: Derek Peak
• Host Institution: Escola Superior de Agricultura Luiz de Queiroz (ESALQ). Universidade de São Paulo (USP). Piracicaba , SP, Brazil
• Institution abroad: University of Saskatchewan (USASK), Canada
• Associated to the scholarship: 18/08586-8 - Broadcast application of limestone and phosphogypsum and the phosphorus forms of an oxisol under no-till, BP.DR

Abstract

Phosphorus (P) is present in soil solution as oxyanions. The mineral phase of humid tropical soils generally present high Al- and Fe-(hydr)oxides contents that adsorb high amounts of P. These soils are generally acidic, and liming is necessary to increase calcium (Ca) and magnesium (Mg) contents, to decrease aluminum (Al) contents as a result of increasing pH. Liming also promotes the increase the quality and quantity of organic matter (OM) in a long-term. The most abundant organic form of P in tropical soils is inositol phosphate, especially its polyphosphorylated form, the myo-inositol hexakisphosphate (IHP6). The IHP6 has high affinity for phyllosilicates and Al- and Fe-(hydr)oxides, and this affinity provides a high stabilization of P in soils by sorption. The IHP6 is mineralized by phytases, which can also be adsorbed by the same minerals. However, it is not known how the functionality of phytase will change if metallic cations bind to the adsorbed IHP6 in distinct pH conditions. In addition to influencing carbon (C) dynamics, the pH variation or the presence of cations may also influence the dynamics of P. Many researchers report the contribution of Ca in the stabilization of organic compounds, but the similar effect is not reported for Mg. In this project it is expected: i) to investigate the IHP6 bonding mechanisms on hematite (Hm) and kaolinite (Kt); ii) determine if the formation of ternary systems (mineral-IHP6-cations) reduces the affinity of phytase for its substrate; iii) to ascertain the improvement in phosphate speciation with the use of µ-XANES and µ-XRD in relation to the bulk XANES samples of an Oxisol; and iv) to obtain chemical evidence that Mg can stabilize organic compounds in a way similar to Ca by means of ternary complexation into Hm or Kt.