Optimizing water–nitrogen coupling for quinoa yield, quality, and resource use efficiency in arid regions

Results indicated that under the <i>W</i>1 irrigation level, increasing nitrogen application enhanced dry matter accumulation. However, under <i>W</i>2 and <i>W</i>3 conditions, dry matter declined when nitrogen exceeded 150 kg/ha, indicating a significant nitrogen threshold effect. A yield response model (<i>R</i>² = 0.945) predicted a maximum theoretical yield of 4,363.91 kg/ha at an irrigation volume of 2,931.59 m³/ha and a nitrogen application rate of 149.24 kg/ha. Optimal grain quality-characterized by fat content of 51.47-55.90 g/kg, protein content of 189.68-199.05 g/kg, and starch content of 581.23-585.96 g/kg-was observed under <i>W</i>2 and <i>W</i>3 combined with <i>N</i>2 and <i>N</i>3 treatments. Regression analyses indicated peak values for water use efficiency (WUE), nitrogen agronomic efficiency (NAE), and nitrogen partial factor productivity (NPFP) at 1.64, 29.72, and 31.92 kg/kg, respectively. Based on these findings, a recommended water-nitrogen management strategy for quinoa production in southern Xinjiang is 2,700 m³/ha of drip irrigation water combined with 150 kg/ha of nitrogen fertilizer, achieving a balance among high yield, resource efficiency, and environmental sustainability.