Effects of wetting agents on water infiltration into poorly wettable sand, dry sod and wettable soils

Summary

Six commercial wetting agents (three nonionic and three anionic compounds) were tested for their effects on water infiltration into poorly wettable sand, a layer of dry bermudagrass sod, and two wettable soils. The poorly wettable sand and the sod of dormant bermudagrass were obtained from an old lawn area, and the wettable soils (silty clay, and saline sodic silty clay loam) from a pecan orchard and a cotton field. The infiltration of tap water (salinity of 0.8 dS m⁻¹ and a sodium adsorption ratio of 5) was measured in laboratory columns using air-dried soil (or sod) samples after initial soil application of wetting agents at rates equivalent to 12 and 24 L ha⁻¹. The stem of the dormant bermudagrass exuded a brownish substance, and was found to be strongly water-repellent. Application of wetting agents markedly improved initial water infiltration into both the poorly wettable sand and the sod. The effect persisted for the entire test period of four irrigations using a total of 10 cm of water. Effectiveness, however, varied significantly among the tested compounds: polyoxyethylene glycol, polyethylene glycol ether and sulfosuccinate compounds were more effective than linear sulfonate or ethoxolated alcohol. The water-repellency of the poorly wettable sand was reduced substantially without wetting agents after two irrigations (using 5 cm of water), and that of the dormant sod after three irrigations (7.5 cm of water). Water infiltration into the air-dried wettable soils also increased significantly in the 1st irrigation (using 10 cm of water) showing 10 to 25% reductions in infiltration time with the application of polyoxyethylene glycol and polyethylene glycol ether.