Recently, increasing frequency and severity of drought events have resulted in significant crop yield reductions worldwide, indicating the critical need for innovative agricultural water management strategies to enhance water use efficiency. Addressing this challenge, we present a novel approach involving the strategic placement of highly hydrophobic sand layers below the subrhizosphere. This method utilizes silica sand modified via a facile, single-step surface treatment, yielding a material with strong hydrophobicity, characterized by a static water contact angle of 133.0 ± 1.0°. Importantly, the modified sand demonstrated stability and retained its hydrophobic properties under simulated adverse agricultural conditions. Systematic investigations of the hydraulic properties revealed that the incorporation of these hydrophobic sand layers substantially controlled the vertical infiltration flux of irrigation water. Specifically, a hydrophobic sand layer with an areal density of 796.5 mg/cm extended the water infiltration time by a factor of approximately 5.5 relative to control soil columns, even following 14 days of sustained irrigation. This engineered impedance promotes saturation within the rhizosphere, thereby potentially enhancing the efficiency of root water uptake. Furthermore, experimental observations indicated a positive correlation between the presence of the hydrophobized subsoil layer and the retention of organic matter within the overlying soil matrix, suggesting ancillary benefits for long-term soil fertility maintenance. Consequently, deploying subrhizosphere hydrophobization using organosilanes as a preplanting soil conditioning treatment presents a potentially more applicable strategy for improving water conservation and soil health, particularly in water-scarce agricultural regions.