Submitted to: Soil & Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 3, 2006
Publication Date: January 15, 2007
Citation: Busscher, W.J., Novak, J.M., Caesar, T. 2007. Organic matter and polyacrylamide amendment of Norfolk loamy sand. Soil & Tillage Research 93:171-178. Interpretive Summary: Because productive sandy coastal soils have poor physical properties, we added environmentally friendly anionic polyacrylamide (PAM) to the soil to foster aggregation. Though PAM had been tried in the 1950’s and was found too expensive, new formulations and techniques might make it feasible today. Two rates of PAM (12 Mg/mole, anionic, and 35% charge density) and five rates of organic matter (OM) were added to a coastal sandy soil to improve soil aggregation and compared to a control. Treatments were incubated in pots in a lab. PAM decreased bulk density and held more water against evaporation than the control; both rates of PAM decreased the amount of water needed to maintain treatments at 10% soil water content. This was heartening because the lower rate of PAM application would be cheaper. Soil strength and aggregation increased with increasing amounts of PAM but showed mixed results when both PAM and OM were added to the soil. PAM increased aggregation in these coastal soils; but more work needs to be done to determine an effective mix of PAM and OM.
Technical Abstract: Loamy sand soils of the SE Coastal Plain often have poor physical properties because they contain cemented subsurface hard layers that restrict root development and infiltration. Physical properties can be improved by adding amendments. Organic residues (OM) and/or polyacrylamide (PAM) were mixed into a blend of 90% E horizon and 10% Ap horizon (to assure microbial activity) obtained from a Norfolk soil (Acrisol or fine-loamy, siliceous, thermic Typic Kandiudult). We hypothesized that incorporation of these amendments would improve physical properties. Pots containing 450 g of soil, OM, and amendment mixtures of 30 and 120 mg/kg of PAM (12 Mg/mole, anionic, and 35% charge density) were incubated for 90 d at 10% (w/w) water content. The pots were leached with 1.3 pore volumes of deionized water. After leaching and equilibrating to stable water contents, cone indices were measured with a 5-mm diameter flat-tipped bench-top penetrometer. Cone indices increased with increasing amounts of PAM but showed no significance when both PAM and OM were added to the soil. When compared to controls, soil mixes with PAM at 120 mg/kg had decreased bulk densities. Soil mixes with both rates of PAM had decreased requirements for water needed to maintain treatments at 10% water contents. Aggregation increased with increasing amounts of PAM but showed mixed results when both PAM and OM were added to the soil. Though PAM improved soil physical properties in these coastal soils, more work needs to be done to determine an effective mix of PAM and OM.