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

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.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Natural Res & Env Sciences

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2022

Author dc:creator

• Xu, Suwei

Contributors dc:contributor

• Arai, Yuji
• Chu, Maria Librada
• Martin, Nicolas Federico
• Sparks, Donald

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

Statement dc:rights

• Copyright 2022 Suwei Xu

Language dc:language

en, eng

Handle dc:identifier

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

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F115762