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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.

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 utilization of low-N tolerant and N-efficifent varieties offers significant benefits in terms of reducing the need for excessive N fertilizer input. Quinoa, a resilient crop for agroecological transition, possesses a wide genetic diversity, making it suitable for selecting genotypes that require less N fertilizer. In this study, the growth and physiological characteristics of nine quinoa genotypes were assessed to determine their low-N tolerance using the fuzzy membership function. Based on comprehensive evaluation indices, three genotypes were identified: low-N tolerant (BL22), intermediately tolerant (A29), and sensitive (G68). These genotypes were exposed to varying N concentrations, including normal (4 mM), low (0.8 mM), and deficient N (no N) conditions. The results indicate that low-N conditions altered root phenotype, with reduced biomass, total protein, and chlorophyll content; increased soluble sugar levels; and inhibited N-metabolizing enzymes (nitrate reductase, glutamine synthetase, glutamate synthase) and N uptake. Under low-N conditions, the tolerant genotype exhibited higher maximal efficiency of photosystem II (Fv/Fm), root vitality, and N content compared to the sensitive genotype. Interestingly, the sensitive genotype displayed elongated and thinner shoots and roots in response to low-N, suggesting that plant height and root length are unreliable indicators of low-N tolerance in quinoa. In contrast, shoot and root dry biomass, Fv/Fm, chlorophyll content, N-metabolizing enzymes, and N content proved to be reliable indicators of low-N tolerance during the early growth stage of quinoa. Overall, these findings highlight the potential of utilizing specific growth and physiological parameters as indicators for screening low-N tolerant quinoa genotypes, thereby reducing dependence on N fertilizers.