|GREEN, V - PURDUE UNIVERSITY
|GRAVEEL, J - PURDUE UNIVERSITY
Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2000
Publication Date: 9/1/2000
Citation: Green, V.S., Stott, D.E., Norton, L.D., Graveel, J.G. 2000. Polyacrylamide molecular weight and charge effects on infiltration under simulated rainfall. Soil Science Society of America Journal. 64:1786-1791.
Interpretive Summary: Surface sealing and erosion on agricultural fields is a severe problem resulting in decreased infiltration, increased runoff, and difficulties with seedling emergence. There is considerable interest in using polyacrylamide (PAM) to control sealing and erosion. Early work showed that low molecular weight PAMs were ineffective, as were PAMs with no charge substitutions. We believe that the effectiveness of different PAM formulation is dependent on the soil type. In this study, we tested PAMs with different molecular weights and degrees of charge substitution (i.e., hydrolysis) for three different soils. We used commercially available PAM formulations ranging from 6-18 million daltons and 20-40% charge substitution. Three soils were used: 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, two processes that break apart aggregates. PAM treated aggregates were more stable than the non-treated aggregates for all three soils. For the Heiden clay, charge density was the critical factor for selecting a PAM that worked, while molecular weight and charge density were equally important in selecting an effective PAM for the Cecil sandy loam. The Fincastle silt loam, which had poor initial structure, responded equally well to all tested PAM formulations. The impact of the research is that a properly selected PAM will allow improved performance and economic savings for land managers and conservationists.
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. We examined 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). PAM treated soil samples were analyzed using a fall velocity settling tube. A slaking index and an aggregate stabilization index were used to compare the treatments. PAM 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. Our results showed the need to select proper PAM formulations for best performance.