Presenter: Joel B. Gruver
Advisor(s): Dr. Michael Wagger
Author(s): Joel B. Gruver
Graduate Program: Soil Science

Title: Air Elutriation: a New Method of Isolating Physical Fractions of Soil Organic Matter

Abstract: Many studies have found physical fractions of soil organic matter to be sensitive indicators of soil management and function. Unfortunately, physical fractionation methods tend to be laborious and often modify the biological, chemical and/or physical characteristics of natural soil constituents. Air elutriation, the sorting of particles with respect to terminal velocity in an air stream, is widely used in seed research and the manufacturing of particulate materials but has received little attention by soil scientists. A commercial seed blower was used to sort batches of whole soil, aggregate size fractions and spherical glass beads. The sorting process occurred within a vertical column with elevated shelves for catching low terminal velocity materials. An adjustable aperture at the top of the column allowed control of air flow rate. A strong linear relationship was observed between glass bead and column aperture size. Whole soil from two long term experiments was fractionated by dry sieving and air elutriation. The permanganate oxidizable carbon (POC) content of a low terminal velocity fraction of whole soil was more sensitive to management than the POC content of aggregate size fractions (<0.25mm, 0.5-1mm, 1.0-2.0mm) or whole soil. In addition, aggregate size fractions (1-2 mm, 0.5-1mm) were sorted using air elutriation. The low terminal velocity components of each size fraction contained more POC and less sand than high terminal velocity components. Air elutriation appears to be a promising technique for quickly and gently isolating physical fractions of soil organic matter.