Fertilizer types and nitrogen rates integrated strategy for achieving sustainable quinoa yield and dynamic soil nutrient-water distribution at high altitude

Quinoa (Chenopodium quinoa Willd.) is a crop particularly adapted to high-altitude environments characterized by significant variability in climate and soil conditions Fertilization is essential for providing nutrients and influencing soil nutrient cycling and hydrological dynamics. This study aimed to optimize fertilizer type and nitrogen (N) application rates to improve soil nutrient availability, moisture retention, and quinoa yield. We examined three fertilizer types: compound fertilizer (NPK), bio-microbial fertilizer (BM), and slow-release fertilizer (SRF), with nitrogen application rates of 90, 120, and 150 kg ha^{- 1}, compared to a control group (CK) with no fertilization. Our results revealed that applying 120 kg ha^{- 1} of nitrogen with SRF significantly reduced soil bulk density, improved water retention beyond 60 cm depth, and enhanced water use efficiency by 9.2-16.2%, alleviating water stress. In conjunction with BM, this nitrogen application increased soil organic matter, alkali-hydrolyzed nitrogen, and the availability of phosphorus and potassium, especially during the grain-filling stage, promoting quinoa growth. Elevated nitrogen rates (120 and 150 kg ha^{- 1}) with BM maximized soil urease and sucrase activities, correlating positively with key soil chemical parameters. Additionally, 120 kg ha^{- 1} of SRF notably boosted quinoa biomass and yield components. Economic analysis indicated that SRF at 120 kg ha^{- 1} nitrogen provided the highest productivity. These results highlight the importance of fertilizer type and nitrogen rates in enhancing soil nutrient status and optimizing water infiltration in high-altitude soils, offering a drought-resistant strategy for quinoa cultivation.