Stability analysis of soil aggregates treated with anionic polyacrylamides of different molecular formulations

Soil sealing and erosion on agricultural fields is a severe problem that often leads to increased runoff and decreased soil quality. Much research has been conducted using polyacrylamide (PAM) to control soil sealing and reduce erosion, yet few studies have attempted to determine the most effective molecular formulation(s) of PAM. 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 PAM solutions 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). The soils used varied in both texture and mineralogy: Heiden clay (fine, smectitic, thermic Udic Haplusterts), Cecil sandy loam (fine, kaolinitic, thermic Typic Kanhapludults), and Fincastle silt loam (fine-silty mixed, superactive, mesic Aeric Epiaqualfs). Soil samples treated with PAMs of different formulations 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 among PAM treatments were observed only for the Fincastle silt loam. When examining slaking and dispersion components together, PAM treated aggregates were more stable than the control for Heiden clay and Fincastle silt loam soils. For Heiden clay, CD was the main factor influencing aggregate stability, whereas CD x MW controlled the stability of Cecil sandy loam. Fincastle silt loam exhibited no preference to a specific PAM formulation factor. Polyacrylamide was effective in enhancing the stability of aggregates; however, it may not be as important in controlling the slaking component specifically.