Interactive effects of salinity and nitrogen fertilization on soil ion accumulation and ion uptake in quinoa

Salinity is a major constraint in arid-region agriculture, where selecting appropriate irrigation water quality and optimizing nitrogen (N) fertilization are critical for maintaining soil health and sustaining quinoa production. This two-year field lysimeter experiment evaluated how different salinity levels (5, 10, 20, and 25 dS m⁻ 1 ) and N application rates (0, 150, and 300 kg N ha⁻ 1 ) affect ion dynamics in soil, nutrient uptake, and crop performance. Results showed a clear management-relevant threshold: quinoa maintained acceptable seed yield at EC e of 13 dS m⁻ 1 under adequate N supply as 150 kg N ha⁻ 1 . Under irrigation water salinity up to 10 dS m⁻ 1 , 150 kg N ha⁻ 1 is recommended to maximize seed yield. However, for highly saline water (20–25 dS m⁻ 1 ), 300 kg N ha⁻ 1 is required to mitigate salt stress and maintain acceptable yield. Increasing irrigation water salinity from 5 to 25 dS m⁻ 1 sharply elevated soil Na⁺ and Cl⁻ (227% increase), and altered the K⁺/Na⁺ balance; however, higher N rates improved plant K⁺/Na⁺ ratios, supporting better ionic homeostasis under salt stress. High salinity reduced N translocation to seeds, shifting more N to vegetative tissues. Overall, the study demonstrates that integrating moderate irrigation water salinity with optimal N fertilization can enhance ionic balance and maintain quinoa productivity under saline conditions, offering practical guidelines for irrigation and nutrient management in salt-affected cropping systems.