TITLE OF THESIS: Non-Destructive Solid-State Investigation Of PEI Agricultural Soils

Date: Monday August 24th, 2020, 1:00 p.m.

ABSTRACT:

Prince Edward Island is a province commonly known for its visually notable red sandy soil, and their prominence in agricultural growth; most notably, potato farming. Potato growth in PEI has become stagnant over the past 10 years. Phosphorus, one of the three main plant macronutrients, can mineralize through interactions with iron and aluminium in PEI soil. While the distinctive red colour of PEI soil is due to large iron content (hematite), aluminium is our prime focus for fixation of phosphorus due to the pH of PEI soil. Default analytical methods, including NMR, for the analysis of phosphorus speciation within soil typically includes extraction protocols and analyses, which only partially represent interactions within a soil matrix in the natural environment. Understanding the mineral profile of PEI soil is crucial in understanding how phosphorus can interact in the solid state, potentially affecting its bioavailability. Thus, we have taken a non-destructive, solid-state chemistry approach in order to analyze soil. Soil samples were analyzed using 31P and 27Al solid-state nuclear magnetic resonance (NMR) spectroscopy. A 27Al chemical environment was discovered in PEI soil that was not reported in literature as a substantial spectral region,for similar soil types. 27Al nuclear relaxation data was observed to gain further insight into aluminium speciation within PEI soil. Powder x-ray diffraction (PXRD) was successfully utilized to characterize the mineral material structure of PEI soil. The aluminium mineral forms detected by PXRD were assigned to their respective 27Al chemical shift. The effect of default extraction methodology, namely the Mehlich-3 extraction, was also explored using ssNMR and PXRD. Synchotron techniques were also used to analyze the solid-state structure of PEI soil. Namely, x-ray absorption of near edge structure (XANES) and scanning transmission x-ray microscopy (STXM) experiments were conducted at the Canadian Light Source in Saskatoon, Saskatchewan. Al K-edge XANES experiments allowed us to examine the overall bulk speciation of aluminium in PEI soil. Al, Fe, and P STXM experiments provided a visual perception to the mineral speciation of PEI soil, allowing us to draw on associations between Al, Fe, and P species present. Our non-destructive analysis of PEI soil allowed us to broaden our perspective of the solid-state structure of PEI soil, while also identifying potential irregularities occurring within it

The presentation and examination will be presented via a web conference. Anyone who wishes to attend the public presentation should contact the grad studies coordinator at gsc@upei.ca to receive the link to the meeting.