Surfactants Effects on Water Retention and Flow in Subsurface Drip Irrigated Unsaturated Soils.

Soil surfactants or wetting agents are reported to improve infiltration, water distribution, and retention properties of unsaturated soils in cropping and turfgrass system. A 3-month long greenhouse experiment has been conducted at New Mexico State University to study the soil water retention behaviors and water flow patterns in loamy sand treated with surfactants ACA 1848 and ACA 2994 (Aquatrols Corp., Paulsboro, NJ) and injected at recommended rates from a subsurface drip irrigation system placed at 10 cm soil depth. Containers measuring 60 cm (length) × 60 cm (width) × 60 cm (height) were packed with a loamy sand and irrigated weekly with potable water at 100% of reference evapotranspiration. The study included the following three treatments: (1) control (no surfactant); (2) ACA 1848 applied once monthly at a rate of 0.47 ml m^-2 (0.174 ml per container); and (3) ACA 2994 applied once monthly at a rate of 2.55 ml m^-2 (0.946 ml per container). Temporal variations of the soil water content at depths of 10, 15, 25, 35 and 45 cm indicated a greater water holding capacity for the surfactant treated soil profiles than for the control treatment. However, measurements at 5 cm depth (soil depth above the drip emitters) revealed a lower moisture content in the ACA 2994 treated soil profile compared to the control and ACA 1848. This study demonstrates that surfactants can be used in arid soils to enhance soil water holding capacity. However, more studies are needed, to evaluate the performance of the tested products on crop growth under real field conditions.