Gary Lehrsch1, Robert Sojka1, Josh Reed1, and Stanley Kostka2. (1) USDA-ARS, Northwest Irrigation & Soils Research Laboratory, 3793 N. 3600 E., Kimberly, ID 83341-5076, (2) Aquatrols Corporation, 1273 Imperial Way, Paulsboro, NJ 08066-1808
Surfactants affect the water relations of water repellent soils but may or may not affect those of wettable soils. We studied the effects of three surfactants, i) Aquatrols IrrigAid Gold®, ii) an ethylene oxide/propylene oxide block copolymer, and iii) an alkyl polyglycoside, along with untreated tap water as a control, each applied two ways, on the water relations of two wettable silt loams, Rad (Xeric Haplocambid) and Latahco (Xeric Argialboll). Each soil was packed 76 mm deep at 1.1 Mg m-3 atop 76 mm of fine gravel in 1.2-m (W) x 1.5-m (L) x 0.2-m (D) soil boxes, with four replicates per treatment. At 46.8 L ha-1, each surfactant was either sprayed onto the soil as a chemigation with the first of two simulated, tap-water irrigations or was sprayed by hand onto the packed soil prior to the first irrigation. Runoff with time and sediment losses from boxes sloped at 2.5% were then measured from a 29-mm irrigation, followed one week later by a 22-mm irrigation, each at 88 mm h-1 intensity. Additional post-irrigation measurements included bulk density, aggregate stability, surface penetration resistance, water content, water retention (at potentials from -100 to 0 kPa), and ponded and tension infiltration at three potentials. In short, the surfactants we studied did not affect the parameters we measured, with one exception. As supply potential decreased from -20 to -60 mm H2O, the Rad’s hydraulic conductivity after the first irrigation decreased more sharply (p < 0.047) for hand-sprayed IrrigAid Gold than for the remaining surfactants or the control, revealing that IrrigAid Gold increased flow through larger pores but decreased flow through pores with diameters ≤ 0.5 mm in the recently treated, nearly saturated Rad silt loam. A better understanding of surfactant effects on water relations of “normal” soils could improve our management of herbicides, fertilizers, and other agrochemicals.