Expanding the Soil Water Characteristic Curve to Feed the World with Less Water.

Soil water matric potential in the plant root zone is frequently modified by natural and anthropogenic modifications of pore size distribution and connectivity. Soil water retention curves predict greater water loss, by drainage, as the texture of root zone regions contain larger pores typical of sandy soils requiring more frequent supplemental irrigation. Occasionally the soil water retention of highly permeable coarse textured sands exhibit greater water holding capacity, due primarily to the presence of accumulated thin layers of alluvial clay exhibiting very low saturated hydraulic conductivity. When these Bt clay layers are present at depths less than 60 cm, volumetric water contents (VWC) are doubled in plant root zones, converting heterogeneously distributed regions of sand soils into sustainable agricultural lands. As global populations increase there are greater demands for identifying arable soils while water supply becomes more limited. We engineered a spatially distributed array of U-shaped subsurface water retention membranes that transform the soil water characteristic graph of naturally highly permeable sand. These new subsurface water retention technology (SWRT) membranes double VWC at 45 to 15 cm soil depths.  Three dimensional spacings of SWRT water-saving membranes are designed for overflow during excessive rainfall events, yet they intercept and retain nearly 100% of precipitation and irrigation water volumes required for maximum plant production. This paper reports how a water impermeable polymer membrane converts marginal sands into sustainable agricultural production lands. Using slopes of these enhanced soil water retention graphs we calculated accelerated water diffusivities along gradients of matric water potentials at multiple soil distances above the spatially distributed array of U-shaped water retention membranes in the root zones. These higher flux rates improved shoot to root ratios of corn plants 2.3-fold and grain yield 243%. In Iraq, soil salinity was reduced within irrigated U-shaped water retaining membranes increasing tomato production by 89% while requiring only 61% of irrigation water. We believe sustainable plant production on these modified sandy soils will continue to improve as more water, nutrients, and organic carbon are retained in plant root zones for longer periods of time. It is anticipated these new SWRT membranes will generate additional innovative opportunities for increasing water and fertilizer use efficiencies that promote plant growth while reducing deep leaching of plant nutrients, pesticides, heavy metals, salts, and other toxic substances in humid, arid and semiarid soils globally.