Nitrogen fertilizers play a critical role in enhancing crop yields; however, excessive application has resulted in significant environmental challenges, including water contamination and increased greenhouse gas emissions. Therefore, improving nitrogen use efficiency is essential for sustainable agriculture. This review based on a systematic search of Web of Science and CNKI for peer-reviewed studies on maize nitrogen efficiency published between 1945 and 2024 (excluding conference abstracts), this review presents the first multiscale synthesis demonstrating how balanced nitrate–ammonium nutrition coordinates N–C metabolism and phytohormone signaling to boost nitrogen use efficiency and stimulate maize growth, with supporting evidence from other crops. By integrating results from hydroponic and field experiments, the review evaluates the influence of mixed nitrogen sources on nitrogen uptake, root morphology, photosynthesis, carbon metabolism, and hormone signaling. Findings indicate that optimal NO₃⁻:NH_4⁺ ratios improve nitrogen absorption through enhanced root development and activation of specific nitrogen transporters. Additionally, mixed nitrogen nutrition increases photosynthetic efficiency, promotes carbon assimilation, reduces energy expenditure, and stimulates auxin-mediated growth. This review shows that balanced nitrate–ammonium co-application synergistically enhances crop nitrogen-use efficiency and yield, provides a theoretical basis for high-efficiency nitrogen-fertilizer development, and helps alleviate environmental pressures, advance sustainable agriculture, and secure food and ecosystem safety. Its efficacy, however, is modulated by soil type, climate, and genotypic variation, necessitating systematic validation and application optimization in future research.

Waterlogging stress has a negative influence on agricultural production, particularly for rapeseed yield in a rice-rape rotation field. To alleviate the profound impacts of waterlogging stress on rapeseed production, a new fertilization with calcium peroxide (CaO₂) was proposed. In this field experiment, with the conventional rape (Brassica napus L.) variety fengyou958 (FY958) and early maturing rape variety xiangyou420 (XY420) as materials, waterlogging was imposed from the bud to flowering stage, and three supplies of CaO₂ (0, C1 for the 594 kg hm^-2 and C2 for the 864 kg hm^-2) were added as basal fertilizer. The results showed that CaO₂ significantly reduced the accumulation of fermentation products in roots and alleviated the peroxidation of leaves. The reduced waterlogging stress promoted the root vigor and agronomic characters, such as branches, plant height and stem diameter, accelerated dry matter and nutrients accumulation, and resulting in 22.7% (C1) to 232.8% (C2) higher grain yields in XY420, and 112.4% (C1) to 291.8% (C2) higher grain yields in FY958, respectively. In conclusion, 594 kg hm^-2 to 864 kg hm^-2 CaO₂ application restored the growth of waterlogged rapeseed leaves, and reduced the anaerobic intensity of root, which enhanced the resistance of plants to waterlogging, and improved crop productivity. In a certain range, the higher CaO₂ application, the more the yield. This study provides a valid method to prevent damage from flooding in crop fields.

Drought represents a paramount constraint on global agricultural productivity, imposing severe limitations on crop yield and quality across diverse agroecosystems. Nitrogen (N), functioning as an indispensable macronutrient fundamental to plant architecture, metabolism, and stress acclimatization, exerts a pivotal influence in modulating plant resilience to water deficit. Substantial evidence accumulated in recent years underscores that optimal N nutrition significantly enhances plant adaptive capacity under drought by improving intrinsic water use efficiency (WUEi), optimizing photosynthetic performance, augmenting antioxidant defense systems, promoting advantageous root architectural modifications, and stabilizing biological N fixation (BNF) symbioses. This comprehensive review synthesizes current knowledge on the intricate physiological and molecular mechanisms underpinning N-mediated drought mitigation. We meticulously examine regulatory roles of N in water relations and hydraulic conductivity, photosynthetic apparatus protection and carbon assimilation efficiency, N metabolic flux and assimilation homeostasis, reactive oxygen species (ROS) scavenging and osmotic adjustment, root system development and resource foraging strategies, BNF system robustness under water stress, and the complex signaling networks integrating N and drought responses. Furthermore, we critically evaluate existing research consensus, identify persisting controversies and knowledge gaps, and delineate future research trajectories and translational challenges. The overarching objective is to furnish a robust theoretical foundation for devising precision N management strategies and advancing the breeding of drought-resilient, nutrient-efficient crop cultivars suited to arid and semi-arid regions facing escalating climate variability.

Purpose Waterlogging stress has a negative influence on agricultural production, particularly for rapeseed yield in a rice-rape rotation field. Calcium peroxide reacts with water to release oxygen, which can serve as an excellent supply. Methods In this field experiment, the conventional rape (Brassica napus L.) variety fengyou958 (FY958) and the early maturing rape variety xiangyou420 (XY420) were used to evaluate the effects of calcium peroxide on waterlogging resistance in a rice-rape rotation field. Waterlogging was imposed from the seedling to flowering stages, and three concentrations of calcium peroxide (0, C1 for the 0.594 kg plot^− 1 and C2 for the 0.864 kg plot^− 1) were added as basal fertilizer. Results Waterlogging decreased the yield of XY420 and FY958 rapeseed by 74.8% and 87.4%, respectively, while the leaf SPAD values decreased significantly by 17.2% and 21.5%. Treatment with calcium peroxide resulted in an increase of 151%-293% in the yield of rapeseed compared with the waterlogged plants. Moreover, calcium peroxide alleviated the peroxidation of leaves and decreased the activities of catalase and superoxide dismutase by 14.2%-44.4% and 10.9%-19.5%. Compared with the waterlogged plants, the contents of abscisic acid and ethylene in the C2 leaves decreased by 37.3% and 33.4%, while the content of gibberellin increased significantly by 44.9%. The belowground parts of the plants were also significantly affected. The treatments with calcium peroxide reduced the activities of fermentation enzymes in the roots, which significantly reduced the accumulation of fermentation products by 25.0%-57.1% and 16.5%-29.4% for lactate and ethanol, respectively. This reduction was owing to the improved levels of oxygen in the root environment that were released by calcium peroxide. Conclusions The application of a suitable concentration of calcium peroxide enhanced the resistance of rapeseed to waterlogging stress, and this study provides a valid method to prevent damage from flooding in rice-rape rotation fields.