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.

Quinoa (Chenopodium quinoa Willd.) is gaining recognition as a pseudocereal due to its nutritional attributes and adaptability to challenging conditions and marginal soils. However, understanding the optimal fertilization for quinoa growth remains a challenge. This study investigates the effects of nitrogen fertilization (0, 90, 120, and 150 kg using urea) on quinoa phenology, growth, and photosynthesis in the Loess Plateau region of China, a critical area facing soil erosion and ecological degradation. The results showed that nitrogen fertilization significantly influenced quinoa phenology, prompting early flowering and shorter growth at an optimum rate of 120 kg ha⁻¹. Nitrogen application enhanced growth traits such as plant height, stem diameter, and chlorophyll content, particularly at the heading and flowering stages. Photosynthesis-related parameters, including net photosynthesis rate, transpiration rate, stomatal conductance, and intercellular CO₂ concentration, were affected by nitrogen application, with higher values observed at 120 kg ha⁻¹. Non-photochemical quenching was significantly increased by nitrogen application, indicating the efficient dissipation of excess energy. The study demonstrated a positive correlation between grain yield and growth traits, photosynthesis-related traits, and chlorophyll content. In conclusion, quinoa yield could be significantly improved at the Loess Plateau region under rainfed conditions by an optimal nitrogen fertilizer rate of 120 kg ha⁻¹, which reduces the growth duration while increasing photosynthesis traits.

The objective of this study was to investigate how nitrogen and slow-release fertilizers affect the traits of leaf senescence and quinoa production in order to explore the optimal slow-release fertilizer and nitrogen fertilizer ratios suitable for quinoa production, as well as to provide theoretical references for the planting of quinoa fertilization methods and fertilizer amount. In this experiment, the main local strain Quinoa 77 was selected as the experimental material, and six treatments were set up: CK: no nitrogen fertilizer; T₁: 100% urea (N); T₂: 100% slow-release fertilizer (C); T₃: 5:5 (C₅N₅); T₄: 3:7 (C₃N₇); and T₅: 7:3 (C₇N₃). This was done in order to investigate how various treatments affect the activities of catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD); malondialdehyde (MDA) content; and yield of quinoa leaves. The findings revealed the following: (1) As the reproductive period progressed, the activities of CAT, POD, and SOD in quinoa leaves treated differently showed a tendency to increase and subsequently decrease, and they reached the peak value at the early stage of filling. The activity of CAT, POD, and SOD in the T₃ treatment was the highest, and the average activities were 3148.74 U·g⁻¹, 2197.84 U·g⁻¹, and 118.51 U·g⁻¹, respectively, which increased by 78.90%, 101.99%, and 108.14%, respectively, compared with CK. The content of MDA continued to increase with the progress of fertility. The average T₃ treatment was 36.41 nmol·g⁻¹, which was 46.87% lower than that of CK. (2) Out of all the treatments, T₃ had the highest yield with an average of 3829.43 kg·hm⁻², T₅ the second with an average of 3313.52 kg·hm⁻², and T₄ the third with 2847.47 kg·hm⁻², which increased yields by 96.18%, 69.75%, and 45.87%, respectively, compared with CK. (3) Yield was highly significantly and positively correlated with thousand kernel weight; number of grains per spike per plant; and the early filling stages of CAT, POD, and SOD sports, and it had a negative, extremely significant correlation with MDA content. Comprehensive analysis showed that slow-release fertilizer and nitrogen fertilizer can improve the antioxidant enzyme activity of quinoa leaves, inhibit MDA content, improve the physiological characteristics of quinoa, and delay the purpose of leaf senescence, with a better effect of yield and income, of which the T₃ treatment had the high-quality impact of increasing yields and was a more scientific and reasonable fertilization method.

Excessive nitrogen fertilization can degrade soil quality by inducing nutrient leaching, disrupting the microbial balance, and impairing plant reproductive growth, ultimately reducing crop yields. Optimizing nitrogen application rates and integrating humic acid fertilizers are promising strategies for enhancing soil fertility and improving agricultural productivity. The experimental design included four nitrogen application rates (N0:0 kg ha⁻¹, N1:120 kg ha⁻¹, N2:150 kg ha⁻¹, and N3:180 kg ha⁻¹) with and without humic acid (H: 1500 kg ha⁻¹). Key findings revealed that: (1) The combined application of humic acid (1500 kg ha⁻¹) and medium nitrogen (150 kg ha⁻¹) significantly increased the contents of soil organic carbon (SOC), total nitrogen (TN), available phosphorus (AP), and available potassium (AK) by an average of 21.7% (p < 0.05), 90.5% (p < 0.01), 59.4% (p < 0.05), and 11.3% (p < 0.05), respectively (two-year mean), with significant interactive effects between nitrogen and humic acid on nutrient accumulation; (2) humic acid supplementation significantly increased soil bacterial abundance and diversity: under the combined treatment of medium nitrogen (150 kg ha⁻¹) and humic acid, the bacterial Ace index (indicating species richness) and Shannon index (indicating community diversity) increased by an average of 0.76% and 0.30%, respectively, compared with the single medium nitrogen treatment (p < 0.05), promoting a more balanced microbial community; and (3) quinoa yields improved by 24.62–66.83% with humic acid application, with the highest yield increase observed under the moderate nitrogen rate (150 kg ha⁻¹) in combination with humic acid. These results demonstrate that integrating humic acid with optimized nitrogen fertilization (150 kg ha⁻¹ N + 1500 kg ha⁻¹ HA) can effectively improve soil nutrients and enhance quinoa productivity. The increases in soil total nitrogen (TN, p < 0.01), available phosphorus (AP, p < 0.05), bacterial Shannon index (p < 0.05), and quinoa yield (p < 0.01) under this combined treatment were all significantly higher than those under single nitrogen fertilization or humic acid application, confirming the synergistic effect of the two fertilizers.