Evaluation Of Infiltration Into Artificial Hydrophobic Sand Influenced By Wetting Agents.

Soil hydrophobicity is a common problem especially for sand-based greens in golf courses across the country.  Wetting agent application is the major method used to reduce the damage caused by the hydrophobic layers on turf.  Despite the tremendous amount of interest among superintendents and academics on this topic, the following question remains unanswered: “Which wetting agent is the best?”  Our inability to resolve this issue is due to a number of factors including use of wetting agents for a wide-range of purposes, highly variable environmental conditions, varying management intensities, and variable degrees of hydrophobicity among different locations and/or rootzone depths.  The objective of this study was to establish a lab-based system to utilize artificial hydrophobic sand for investigation of water infiltration as influenced by wetting agents.  Fresh USGA grade sand was treated with octadecylamine with various rinsing and mixing steps before testing the hydrophobicity of the sand.  Water droplet penetration tests revealed the extreme (> 1hr) hydrophobic nature of the hydrophobic sand at a bulk density of 1.7 g/cm³.  A second method, the ethanol droplet test (MED), revealed that the hydrophobic sand had an MED value of 7.2 M, which is far beyond the level 4 extreme water-repellency category with a threshold MED of 5.2 M.  To test the influence of various wetting agents on water infiltration, artificial hydrophobic sand was packed to a bulk density of 1.7 g/cm³ in PVC tubes (5.08 cm diameter by 20 cm length).  A Mariotte bottle was connected to the PVC tubes and placed on a scale at a proper height to maintain a consistent 4.4 cm hydraulic pressure head.  Six selected wetting agents were applied under a consistent lab temperature of 22 °C at reduced rates (25% of the labeled rates).  Infiltration was recorded for 30 min after wetting agent application, and the saturated hydraulic conductivity (Ksat) was calculated under steady infiltration rates.  Seepage timing was recorded as the required time for solution to exit the sand column.  After the infiltration experiment, the sand columns were disconnected and dried in an oven at 55^o C until a constant weight was reached.  The tubes were then reconnected to the Mariotte bottle with tap water only as treatment, and infiltration rate was re-measured.  This experiment was designed as a complete randomized design with three replications, and repeated once.  Results show a significant difference amongst the different wetting agents in terms of seepage, infiltration, Ksat, and their effects on re-wettability with water only.  Details of the infiltration and re-wettability as influenced by various wetting agents will be presented.