From Water Delivery to Root-Zone Engineering: Drip Irrigation Drives Adaptive Root Architectural Plasticity and Enhances Spatiotemporal Root–Water Coupling in Maize

The shift from furrow irrigation (FI) to mulched drip irrigation (DI) drives adaptive restructuring of maize root architecture, strengthening spatiotemporal root-soil water coupling. Conventional FI often leads to a spatial mismatch between root distribution and water supply, constraining water productivity in arid regions. Using a three-year field experiment (2019–2021) in Xinjiang, China, this study examined how DI reshapes maize root architecture in three dimensions and affects grain yield under contrasting hydrological conditions. Results demonstrate that DI systematically reconfigures root spatial deployment, promoting a “fine-and-dense” root phenotype. Compared to FI, DI increased fine and medium root length by 35.0–38.6% in the emitter-proximal zone (0–10 cm) and concentrated 78.2% of absorptive roots within the upper 0–20 cm. Vertical root distribution followed an exponential decay pattern, with significantly steeper gradients under DI-root length at 10 cm depth was 303.4% (2019) and 50.4% (2020) higher than under FI (p < 0.05). In contrast, FI promoted deeper root exploration, showing a 49.1–66.1% advantage at 40 cm depth. Root restructuring proved hydrologically conditional: DI increased root length density (RLD) by 224.6% under drought conditions (2019) but only by 29.1% under ample moisture (2021). This trend reversed at the R3 stage, where FI achieved 117.2% higher RLD than DI (p < 0.05). Importantly, topsoil RLD mediated the pathway from irrigation to yield (R2 = 0.87, p < 0.001), identifying spatial root–water coupling as the dominant mechanism. These findings advance irrigation management by accounting for root architectural responses to localized water delivery, providing theoretical guidance for precision agriculture in arid environments.