Surfactant Effect on Artificially Induced Repellent Sand.

The efficacy of surfactants (SURF) on soil water repellency (SWR) is difficult to study in the field due to the spatial variability within the soil profile. To study the effects of SWR, stearic acid (SA), a naturally occurring organic acid, has been used to make sand hydrophobic. The effect of SURF on SWR in soils hydrophobized with SA has not been evaluated. The objective of this trial was to determine if a SURF would reduce contact angle (CA) of a SA treated sand. A greenhouse trial was conducted to determine the effect of a single SURF application on an SA induced water repellent sand (HSS). Prior to surfactant application, the contact angle of a 100% HSS, a 90:10 SAND:HSS, a 50:50 SAND:HSS v/v and 100% SAND (SAND) was 115, 93.3, 98.3 and 0, respectively.  Soils were placed in containers in a greenhouse and either irrigated or remained dry before a one-time application of an alkyl terminated block copolymer SURF. After 48 hours, soil columns were divided into 4 depths: 0-2.5 cm, 2.5-5 cm, 5-7.5 cm and 7.5-10 cm and hydrophobicity was measured as CA using a tensiometer. Hydrophobicity increased in SAND (25°-64°) after SURF application. However, in previous research, water alone increased CA in SAND therefore it is difficult to determine if SURF or water increased the CA on SAND. Contact angle was significantly reduced in SAND at all depths after SURF application if dry prior to application.  Contact angle in a 90:10 HSS:SAND, was reduced by SURF only at the 0-2.5 cm depth and remained unaffected by SURF in the 50:50 SAND:HSS and 100% substrates. This research demonstrates that SA is an effective means of inducing severe SWR on sand. However, once sand is hydrophobized, it was difficult to make it hydrophilic again with a one-time SURF application. This data also suggests that this SURF was more successful if applied when sand was dry rather than wet. Future research should investigate the role treated municipal water has on a hydrophilic soil.