Soil Phosphorus Biogeochemistry

The distribution and speciation of phosphorus (P) in the environment has implications for agriculture, water quality, and terrestrial and marine ecosystem processes (e.g. Feely et al. 1991; Kruse et al. 2007).  Recent advances in our understanding of P biogeochemistry in heterogeneous natural materials have been fueled by synchrotron radiation X-ray spectromicroscopy (Brandes et al. 2007; Diaz et al. 2008). In soils, P speciation research is primarily based on operationally defined methodologies.  At UMN, we are identifying the speciation of P in soils with a long history of P amendments and controlled agricultural management. This project is being led by postdoctoral researcher Dr. Shahida Quazi, and is a collaboration between Paul Bloom and Brandy Toner.    

Spring 2009

We traveled to the Advanced Photon Source at Argonne National Laboratory in Illinois twice this spring to collect P XANES data for soils at a 50 nanometer spatial scale. The beamline we use is 2-ID-B, and we work with Dr. Ian McNulty. The first trip was made by Brandy Toner, Shahida Quazi, and Nick Pester. During this first visit to beamline 2-ID-B, we had a goal of testing the compatibility of our samples with the instrument capabilities. We successfully collected X-ray fluorescence (XRF) maps for our surface soils, and confirmed that P is not evenly distributed among soil aggregates.

Nick Pester and Shahida Quazi at the X-ray microscope controls (APS 2-ID-B)

The Advanced Photon Source - outside

On our second visit to 2-ID-B, Shahida brought Paul Bloom and visiting Ph.D. student Sofia Oufqir. This time, our goal was to collect P XANES spectra for the P amended soils with management histories of corn, grass, and a control. The XANES (X-ray absorption near edge structure) spectra will be used to decipher the form of P present in soil aggregates.

Ian McNulty at setting up the microscope

Soil suspensions

The sample preparation requires a steady hand. A very small volume of soil suspension is placed on an extremely fragile membrane window.

Shahida in the laboratory prepping samples

Sofia at the ligh microscope in the lab

Ian and Shahida working

...for her turn to drive

X-ray absorption spectromicroscopy is an exciting tool for the study of soil biogeochemistry, but it takes a lot of training to use this tool effectively.