Submitted to: Soil Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/2/2004
Publication Date: 8/15/2004
Citation: Green, V.S., Stott, D.E., Graveel, J.G., Norton, L.D. 2004. Stability analysis of soil aggregates treated with anionic polyacrylamides of different molecular formation. Soil Science. p. 573. Interpretive Summary: Soil sealing and erosion on agricultural fields is a severe problem resulting in decreased infiltration rates, increased runoff, and difficulties with seedling emergence, and decreased soil quality. There has been considerable interest, especially in the western part of the United States, in using polyacrylamide (PAM) to control soil sealing and reduce erosion. The molecular weight of PAM can be manipulated, ranging between a few thousand to 20 million grams per mole. The degree (%) of polymer hydrolysis can also differ by the controlling the number of side group substitutions. Little work has been done to determine which PAM formulation is the most effective for controlling problems related to surface sealing on various soil types. Since the first step in surface sealing is the breakdown of surface aggregates into fine soil particles, we chose to examine the ability of a range of PAM formulations to stabilize soil aggregates. Early work showed that low molecular weight PAMs were ineffective, as were PAMS with no charge substitutions. We used commercially available PAM formulations ranging from 6 million to 18 million daltons and 20-40% charge substitution (>40% is not readily available). Three soils were used that varied in both texture and mineralogy: Heiden clay from Texas, Cecil sandy loam from Georgia, and Fincastle silt loam, from Indiana. Treated samples were analyzed for their ability to withstand slaking and dispersion, which are two processes that break apart aggregates. PAM treated aggregates were more stable than the non-treated aggregates for all tested soils. For the clay soil, charge density was the critical factor for selecting a PAM that worked, while both criteria were important in selecting an effective PAM for the sandy loam. The Fincastle silt loam, which had poor initial structure, responded equally well to all tested PAM formulations. It is clear that a single PAM formulation will not be the most effective on all soils, and that a variety of PAMs need to be considered before selecting the best one for use on a given field.
Technical Abstract: Soil sealing and erosion on agricultural fields is a severe problem resulting in increased runoff and decreased soil quality. Much research has been conducted using polyacrylamide (PAM) to control soil sealing and reduce erosion, yet little has been done to determine the most effective molecular formulation. Our objective was to examine the ability of a range of PAM formulations to stabilize soil aggregates. We hypothesized that PAM would perform differently on an assortment of soil types with varying optimum formulations and effectiveness. The PAMs studied included combinations of three molecular weights (MW: 6, 12, and 18 Mg mol-1) and three charge densities (CD: 20, 30, and 40% hydrolysis). Three soils were used that varied in both texture and mineralogy: Heiden clay (fine, smectitic, thermic Udic Haplusterts), Cecil sandy loam (clayey, kaolinitic, thermic Typic Kanhapludults), and Fincastle silt loam (fine-silty mixed, mesic Aeric Epiaqualfs). Treated samples were analyzed using a fall velocity settling tube. A slaking index (SI) and an aggregate stabilization index (ASI) were used to compare the treatments. Polyacrylamide enhanced resistance to slaking of Fincastle silt loam, but not Heiden clay or Cecil sandy loam. Furthermore, differences between PAM treatments were only observed for the Fincastle silt loam. When combining slaking and dispersion components, PAM treated aggregates were more stable than the control for all tested soils. For Heiden clay, CD was the main factor influencing aggregate stability while CD x MW controlled the stability of Cecil sandy loam. Fincastle silt loam exhibited no preference to a specific PAM formulation factor.