Effect of biochar and superhydrophobic sand mulches on evaporation and water holding capacity in sandy soils

Realizing high irrigation efficiency in hot and arid lands is a daunting challenge due to the significant percolation and evaporation losses. Sandy soils exacerbate the situation due to their low water holding capacity that also leads to nutrients leaching. In response, we have developed two soil amendment technologies, namely SandX and Biochar, for boosting soil’s water-holding capacity and curtailing evaporative losses, respectively. Specifically, SandX is a superhydrophobic material comprised of silica sand grains coated with ~20 nm-thick paraffin wax, and the biochar was derived from the pyrolysis of date palm leaves at ~500 °C. We investigate the effects of these materials on the hydraulic properties of a sandy soil (A3 - fine sand ASTM D3282) via pot studies. Experiments revealed that when SandX is applied as a 5-10 mm-tick mulch over the sandy soil in pot studies (transient state; initial soil moisture 22wt%; final soil moisture 10wt%), the evaporation loss was reduced by 54% and 70% respectively relative to the sandy soil (8.35 mmH₂O/day) under an average of 40 °C and 60% relative humidity. Pot-holding capacities (PHC) for water were determined gravimetrically for sandy soil (23.63% gH₂O/g of dry soil) and BC at (a) 2 and (b) 5wt% in sandy soil. PHC increased by (a) 11% and (b) 51%, respectively for the biochar treatments. The synergic effects of SandX and biochar as a function of biochar particle size and mass fraction in the soil will be presented. Our presentation will demonstrate the potential of SandX and datepalm biochar in curtailing high evaporation rates and percolation, respectively, in sandy soils in arid lands.