Soil water distribution and dynamics across prescribed capillary barriers under evaporating surfaces

Engineering soil substrate using a porous composite constructed by a block-structured design (BSD), offers an innovative water-saving approach for high-cash crops in arid regions. We report modeling and experimental studies of the effects of two geometries: a single block (1L) and two stacked blocks (2L) BSD designs on evaporative losses and water distributions in laboratory column experiments involving wetting and evaporation cycles. A reasonable agreement between water content measurements and numerical simulations (HYDRUS 2D/3D code) is demonstrated (7.2E-2<RMSE<1.1E-1, -5.7E-1<NSE< 5.6E-1and 9.4E-1<d < 9.5E-1). The 2L-BSD showed three times slower evaporation rate than 1L-BSD during the drying phases. The presence of a horizontal sand layer at the middle of the 2L-BSD disrupted the hydraulic continuity to the surface, thus inhibiting evaporation from the bottom BSD in the 2L design. Our long term field experiment of 2L-BSD with date palm showed water savings of up to 13.3% to 52% than standard sand mulch soils. Our results illustrate the crucial role of porous media engineering in promoting infiltration after irrigation events or occasional rainfall and sheltering soil water smartly preserved in the root zone from evaporation that is of paramount importance for increasing water use efficiency in desert agriculture.