Competitive sorption of phytic acid and phosphate in agricultural soils and at the amorphous aluminum oxyhydroxide-water interface

Xu, Suwei

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https://hdl.handle.net/2142/115762 Copy

Description

Title

Competitive sorption of phytic acid and phosphate in agricultural soils and at the amorphous aluminum oxyhydroxide-water interface

Author(s)

Xu, Suwei

Issue Date

2022-04-21

Director of Research (if dissertation) or Advisor (if thesis)

Arai, Yuji

Doctoral Committee Chair(s)

Chu, Maria Librada

Committee Member(s)

• Martin, Nicolas Federico
• Sparks, Donald

Department of Study

Natural Res & Env Sci

Discipline

Natural Res & Env Sciences

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• organic phosphorus
• IHP
• aluminum hydroxide
• adsorption
• in situ
• solution NMR
• ratio

Abstract

Phosphorus (P) loss from agricultural land is one of the major causes of water quality degradation in fresh water and seawater. Numerous studies documented phosphate transport from intensively managed agricultural soils to water but disregarded the fate of organic P (Po) in the soil-water environment. Although phosphate and Po are known to accumulate in soils, the Po adsorption process in P-rich soils is poorly understood, especially the effects of reaction conditions (e.g., a ratio between Po and phosphate) on the Po adsorption mechanisms in soil minerals. The objective of this study was to understand the effects of reaction conditions (e.g., phosphate and the ratio of Po and phosphate, addition sequence of phosphate and Po) on the Po adsorption in soils and soil minerals. In the first chapter, the ratio between Po and phosphate was investigated in various agricultural management systems (e.g., manure and fertilizer applied). The goal of this chapter was to understand the realistic Po/phosphate ratio in agricultural systems. Overall, the accumulation of Po and phosphate was agricultural management specific. The Po/phosphate ratio was significantly greater in the manure-amended pasture (~ 0.54) than the fertilizer applied cropland (~ 0.42). Using the Po/phosphate ratio that is relevant to conventional agricultural systems, in the second and third chapter, the competitive adsorption of a common Po species, inositol hexakisphosphate (myo-IHP), and phosphate was investigated in a model soil mineral, amorphous aluminum hydroxide (AAH), using batch adsorption experiments and solution 31-P Nuclear Magnetic Resonance spectroscopy (NMR). In the absence of phosphate, myo-IHP adsorbed strongly in AAH with adsorption maxima of IHP ~ 312.50 mmol/kg and formed inner-sphere surface complexes via three of six phosphate functional groups (i.e., mainly with P4,6, P2, and P1,3) coordination on the mineral surfaces. Using both phosphate and myo-IHP, the effects of simultaneous addition and addition sequence on the adsorption mechanism of myo-IHP in AAH were also evaluated. When two ligands were simultaneously added, two functional groups (P2 and P1,3) mainly interacted with the mineral surface and competed for the surface site with phosphate. An increase in the Po/phosphate ratio resulted in the new coordination of P4,6 and P5 functional groups. When myo-IHP was pre-adsorbed before the phosphate addition, several functional groups (P1,3, P2, P5, and P4,6) were coordinated on the AAH surface. This surface coordination was insensitive to changes in the ratio. Interestingly, when phosphate was added first, the coordination of the P functional group was sensitive to the ratio. The surface coordination changed from P2/P5 to P2 and P1,3 with increasing the ratio. This study found that the Po and phosphate ratio and the addition sequence were important factors influencing the surface coordination of myo-IHP in soil minerals. The soil conditions alter the adsorption affinity of Po in soil minerals affecting phosphate bioavailability. This understanding provides insight into describing the degree of Po and phosphate accumulation and predicting P bioavailability in different agricultural systems.

Graduation Semester

2022-05

Type of Resource

Thesis

Copyright and License Information

Copyright 2022 Suwei Xu

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