Application of Semi-Hydrophobic Layers to Decrease Bare Soil Evaporation

Evaporative water loss from bare agricultural soils is a primary area of water conservation research. Mulching is the commonly utilized method to decrease evaporative water loss. The most commonly utilized mulch is nonbiodegradable polyethylene sheeting because it tends to decrease evaporative water loss and increase crop yields more than environmentally friendly mulches. This study aimed to test the utility of sand coated with polymerized soybean oil (i.e., hydrophobic sand) as a treatment to reduce bare soil evaporation and an alternative to current practices. Evaporation rates were measured in laboratory soil columns containing both treated and untreated soils. Treatment parameters were varied systematically (i.e., ~1 cm and ~2 cm layer thicknesses, medium and coarse grain sizes of treated soil). Treated soil was Water Drop Penetration Time (WDPT) tested before and after degradation testing, and physical properties of the treated soil including hydraulic conductivity and porosity were also measured. Pre degradation WDPT tests showed that the polymerized soybean oil slightly hydrophobized the sands, and the treated sands significantly decreased evaporative water loss (>90%) prior to the bare soil's Stage 2 evaporation. Furthermore, the coarser hydrophobized sands were minorly less effective at decreasing evaporation as the medium grain hydrophobic sands, but the coarser grains had a WDPT of less than ~3 seconds (less after wetting) and could therefore theoretically allow for water infiltration.