Polymer effects on water infiltration and soil aggregation

The effectiveness of synthetic polymers as soil conditioners was found to depend on polymer properties. We hypothesized that the polymer penetration and movement into the aggregate are important factors in reduction of surface sealing. The effect of nonionic (P-101), cationic (CP-14), and anionic [Complete Green (CG)] commercial polymers on infiltration rate (IR) and aggregate formation was studied in a sandy loam (Typic Rhodoxeralf). Amounts of 25, 50, and 75 kg ha^-1 of each polymer were spread across the soil surface. After air drying, the surface was subjected to 68 mm of distilled water with impact energy of 18.1 J mm^-1 m^-2 using a rainfall simulator. Soil particle association was studied in 10% (w/v) soil suspension with polymer concentration ranging from 0 to 50 g m^-3. Viscosity values 3.3 109, and 165 mPa s were determined in 5 g L^-1 of P-101, CP-14, and CG solutions at shear rate of 27 s^-1, respectively. The final IR values were 63 to 30 mm h^-1 at P-101, 18 to 24 mm h^-1 at CP-14, and 18 to 30 mm h^-1 at CG, compared with 8 mm h^-1 in untreated soil. The critical time values in suspensions with different concentrations of polymer were 4.3 to 2.7 min for P-101, 1.0 to 3.4 min for CP-14, and 1.0 min for CG. The critical time indicates the size of the aggregate formed in a suspension; the lower the critical time, the larger the aggregates. It was suggested that because the particle surfaces are exposed to polymer molecules in suspension, the large molecule of CG could tie more suspended particles to form aggregates. The greater effectiveness of P-101 in preventing sealing was probably due to its ability to penetrate into aggregates, because of its small molecular size and low viscosity in solution.