Polyacrylamide molecular weight and charge effects on infiltration under simulated rainfall

Soil sealing is a severe problem worldwide. Increased runoff and decreased seedling emergence cause on- and off-site problems affecting farmers and co mmunities. One possible soil settling control measure is the application of polyacrylamide (PAM). Little is known about the interaction of specific PA Ms with soils of differing characteristics. This study was conducted to exa mine the relationship between different PAMs and soils of varying character istics. We examined PAM charge densities (CD) of 20, 30, and 40% hydrolysis with molecular weights (MW) of 6, 12, and 18 Mg mol(-1). The soils used we re Heiden clay (fine, smectitic, thermic Udic Haplustert), Cecil sandy loam (clayey, kaolinitic, thermic Typic Kanhapludult), and Fincastle silt loam (fine silty, mixed, mesic Aeric Epiaqualf). Polyacrylamide (20 kg ha(-1)) w as sprayed onto the soil in liquid form. Soil material was exposed to rainf all simulation in the laboratory. Infiltration rate was used as an indicato r of soil surface sealing. Polyacrylamide increased infiltration rates on a ll three soils relative to the control. Twenty and 30% CD PARE performed be st in maintaining high infiltration rates on Heiden clay. The 12 Mg mol(-1) MW formulations worked best for Cecil sandy loam. Fincastle silt loam show ed no preference for a particular PAM formulation. Polyacrylamide increased final infiltration rate by as much as 3- to 5-fold for these soils. Differ ent PAM formulations provided differing degrees of soil protection, varying between soils. Understanding the interaction of different soils with vario us PAM formulations will enable PAM users to select the best PAM product fo r their soil conditions.