Modern agriculture, the basis of our civilization, provides sustenance for over 7.9 billion people. However, considering the increasing global population and rising living standards, our food production must to grow by ~50% by 2050. Further constraints of limited arable land, freshwater resources, and the threatening effects of climate change, put our food security at risk and call for multifaceted technological intervention. Currently, irrigated agriculture, while only accounting for 20% of cultivated land, contributes 33%-40% of the total food production. Therefore, irrigated agriculture in arid and semi-arid lands can help us address this complex food–water–climate challenge. However, aridlands are characterized by low precipitation, immense evapotranspiration losses, which is often compensated unsustainably by colossal amounts of freshwater. Evaporation from the topsoil in aridlands remains inadequately tackled. For instance, while plastic mulches have been demonstrated to restrict evaporation, their cost, fragility, lack of reuse, and eventual disposal in landfills limit widespread acceptance. In response, we have conceptualized, developed, and field-tested superhydrophobic sand (SHS), a bio-inspired enhancement of common sand with a nanoscale coating of wax. When a 5-10 mm mulch of SHS is applied on top of subsurface-irrigated soil, the evaporation is dramatically reduced; higher soil moisture boosts plant health, biomass, and yields. Our multi-year field trials of SHS application on tomato (Solanum lycopersicum), barley (Hordeum vulgare), and wheat (Triticum aestivum) crops have consistently demonstrated significant enhancement in grain yields ranging from 17%–73%. In this dissertation, we present our translational surface science research spanning materials development and characterization, mass transfer studies and mathematical modeling, and greenhouse and field experiments. To gain insights into the mulching capacity of water-repellent granular media such as SHS, we present an encompassing novel modeling approach based on particle–particle and liquid–particle forces to accurately capture the fate of evaporating liquid marbles. Then, we explain the origins of SHS superhydrophobicity and provide mechanistic insights into SHS mulching action. Subsequently, we present the data from the field trials to demonstrate how SHS shifts the water balance towards higher crop yields. We close the dissertation with SHS lifecycle analysis and environmental impact and practicality considerations.

The importance of several factors in limiting recovery from defoliation was investigated in field-grown plants of Agropyron desertorum and Agropyron spicatum exposed to drought , natural or irrigated conditions. Leaf extension rate, components of leaf area production, number of metabolically active axillary buds and carbohydrate availability were examined on the same plants immediately after defoliation and/or in the following spring from 1984 until 1986. The diurnal course of leaf growth did not relate to turgor pressure in the expanded portion of leaf laminae. Rather growth was apparently associated with air temperature. Leaf extension rate was lower under drought than under better moisture levels during 1984 to 1986. For both species, reduced growth rates and shorter growth periods resulted in reduced tiller height, leaf number and leaf size under drought compared with natural or irrigated conditions in 1985 and 1986, but not in 1984. As a result, leaf area and/or yields were also lower under drought in 1985 and 1986, and lowest under drought plus defoliation in 1986. Production of daughter tillers immediately after defoliation was also lowest under drought. Regrowth capacity of both species was not limited by axillary bud number, size or viability immediately after defoliation under any water level in 1986. In early spring, however, tiller number and growth were lower on clipped than on unclipped plants of both species under drought and irrigated conditions in 1986, and under all water levels in 1987; this resulted in considerably reduced photosynthetic canopies on clipped plants. Crown and root total nonstructural carbohydrate (TNC) pools were higher under drought than under better moisture levels in A. desertorum and A. spicatum in early spring 1986. These high pools of TNC apparently enhanced the production of etiolated regrowth in both species when meristematic limitations did not exist in early spring. The productive potential of both Agropyron species will probably not be affected following a late and severe defoliation under drought. However, vegetative growth and/or productivity, and probably the persistence of these species in the community, will be reduced after two or more years of late and heavy defoliations under drought.