Synergistic optimization of water and nitrogen use efficiency in quinoa (Chenopodium quinoa Willd.): Interplay of nitrogen fertilization and plant spacing

Row spacing and nitrogen rates have a significant impact on nitrogen-water interactions in crops, potentially mitigating drought stress through reduced evapotranspiration. The goal is to assess the effect of row spacing and nitrogen levels on water and nitrogen dynamics in quinoa and the surrounding soil. We conducted a two-year field experiment in Niangzishen Township, Jingle County, Xinzhou City, Shanxi Province to evaluate three nitrogen fertilizer levels (N1: 90 kg/ha; N2: 120 kg/ha; N3: 150 kg/ha) and three row spacing configurations (R1: 20 cm; R2: 40 cm; R3: 60 cm). Results revealed wider row spacings notably boosted quinoa yield and components, with R3 outyielding others by 3.22–87.17 % (2023) and 3.97–113.68 % (2024); low row spacing (R1) had the best water-holding capacity, especially in 2023, up 7.29–21.7 % (ear emergence) and 7.13–19.54 % (maturity) vs. others; at maturity, R3 had the highest deep soil water under all nitrogen levels, averaging 6.37–23.47 % (2023) and 12.25–15.13 % (2024) above R1 and R2; the medium row spacing (R2) and nitrogen level (N2) had the most significant effect on increasing plant dry matter and nitrogen accumulation, with the highest nitrogen allocation to grains (49.26 %); plant water use efficiency (WUEp) and water productivity (WPC) also reached the same effect at R2N2, significantly increasing WUEp (34.93 %); N2R2 improved nitrogen uptake efficiency (NUPE, 54.17 %), production efficiency (PFP, 67.04 %), and nitrogen harvest index (NHI, 52.5 %) compared to other treatments. This study elucidates the regulatory mechanism of row spacing and nitrogen coupling on soil water-nitrogen dynamics and quinoa growth, providing a scientific basis for high-efficiency and water-saving quinoa cultivation in semi-arid regions. • Optimal N and row spacing enhance water and N use and distribution. • Narrow row spacing benefits soil water storage but reduces N uptake. • Proper water shortage benefits quinoa's N uptake and water use efficiency. • Increasing row spacing can promote the transfer of N from stems or leaves to seeds. • Extra nitrogen boosts soil moisture uptake and enhances water use efficiency.