Enhancing maize yield and water productivity through coordinated root-shoot growth under mild water stress in dense planting

Context: For a long time, the ultimate objective in arid and semi-arid agricultural production areas has been to optimize yield while ensuring efficient utilization of agricultural water resources. This objective can be realized through a judicious integration of dense planting and regulated deficit irrigation (RDI). Currently, it is not clear how these two agronomic measures regulate maize yield by affecting root-shoot coordination. Objective: This study aimed to examine the impacts of planting density (PD) and RDI on leaf area index (LAI), fractional interception of photosynthetically active radiation (FIPAR), radiation use efficiency (RUE), root growth, dry matter distribution, root-shoot ratio (RSR), water productivity (WP), nitrogen partial factor productivity (PFPN), and maize yield. Elucidated the relationship between soil water content (SWC) and root development within different soil layers and to quantify how root characteristics correlate with WUE and yield. Methods: A two-year field trial (2020-2021) was conducted on Xianyu 335 for this study. Set two PD treatments (D1: 70,000 plants/ha, D2: 90,000 plants/ha) and three water treatments, (W1: full irrigation, W2: mild water deficit 2/3W1, W3: moderate water deficit 1/2W1). Results: Dense planting significantly increased the LAI of the population. The FIPAR and RUE of the middle canopy were enhanced, optimizing the canopy structure. Under the D2 treatment, a greater distribution of roots occurred in the topsoil (0-20 cm). Sufficient water availability augmented both the proportion of root mass and the absorption area in deeper soil, thereby promoting the accumulation of dry matter above ground. The RSR decreased with increasing water stress. Under the D2W2 treatment, a positive correlation was observed between SWC and root characteristics across all soil layers, particularly at depths of 60-100 cm. This suggests that moderate water stress application improves water utilization by roots in the deeper soil. Over the two growing seasons, D2W1 resulted in the highest yield and PFPN. Although the yield under the D2W2 treatment decreased marginally by approximately 2.43-3.90 % compared to D2W1, this treatment significantly enhanced WUE (2020: 11.80 %, 2021: 14.29 %) and middle canopy RUE (2020: 13.85 %, 2021: 17.07 %). Conclusions and implications: D2W2 is a planting pattern suitable for maize production in Northwest China (NWC). This approach promotes root-shoot coordination and enhances the use of soil moisture by the root system.