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 communities. One possible soil settling control measure is the application of polyacrylamide (PAM). Little is known about the interaction of specific PAMs with soils of differing characteristics. This study was conducted to examine the relationship between different PAMs and soils of varying characteristics. 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 were 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)) was sprayed onto the soil in liquid form. Soil material was exposed to rainfall simulation in the laboratory. Infiltration rate was used as an indicator of soil surface sealing. Polyacrylamide increased infiltration rates on all three soils relative to the control. Twenty and 30% CD PARE performed best in maintaining high infiltration rates on Heiden clay. The 12 Mg mol(-1) MW formulations worked best for Cecil sandy loam. Fincastle silt loam showed no preference for a particular PAM formulation. Polyacrylamide increased final infiltration rate by as much as 3- to 5-fold for these soils. Different PAM formulations provided differing degrees of soil protection, varying between soils. Understanding the interaction of different soils with various PAM formulations will enable PAM users to select the best PAM product for their soil conditions.