Mildly hydrophobic biobased mulch: A sustainable approach to controlling bare soil evaporation

Mulching with polyethylene film is the conventional approach to decrease evaporative water loss from agricultural soils, but it is not environmentally sustainable. In this study, a laboratory experiment was conducted to test the potential utility of partially polymerized soybean oil (PSO) coated sands as a surface treatment to reduce bare soil evaporation. Evaporation was tracked for 23.8 d from saturated sand columns treated with a surface layer (1 or 2 cm) of either coated medium sand (MS‐PSO) or coated coarse sand (CS‐PSO). The water drop penetration time (WDPT) was used to assess the hydrophobicity of fresh PSO‐coated sands; the saturated hydraulic conductivity ( K s ) and particle density (ρ s ) were measured as well. The WDPT was also tested on MS‐PSO and CS‐PSO samples aged in four separate environmental conditions for 20–21 d. Both PSO‐coated sands were mildly hydrophobic, and the surface treatment layers reduced evaporative loss by 83–96% over bare soil, which is similar to previous work using extremely hydrophobic chemically treated sands. Freshly coated MS‐PSO had a higher WDPT score and lower K s than CS‐PSO. After the environmental aging tests, the MS‐PSO and CS‐PSO samples remained mildly hydrophobic. Notably, CS‐PSO had a low initial WDPT (∼1.09 to ∼2.58 s) and a high K s (2.66 × 10 −1  cm s −1 ), suggesting coarse PSO‐coated sands will permit infiltration. Given these findings, PSO‐coated sand has the potential to be developed into a sustainable alternative to polyethylene film mulch.