Molecular Soil Biology 2025, Vol.16, No.4, 162-174 http://bioscipublisher.com/index.php/msb 167 environmental footprint of rice cultivation but also lowers input costs, making the practice more sustainable and economically viable for farmers. 4.3 Integrated nutrient management (INM) Integrated Nutrient Management (INM) combines the use of organic fertilizers, biological inoculants, and chemical fertilizers to optimize nitrogen availability and improve NUE. This holistic approach leverages the strengths of different nutrient sources to enhance soil fertility and crop productivity. Organic fertilizers, such as compost and manure, improve soil structure and microbial activity, which in turn enhances N mineralization and availability to plants (Novair et al., 2021). Biological inoculants, including nitrogen-fixing bacteria and mycorrhizal fungi, further contribute to N uptake and utilization by the rice plants. Combining these organic and biological inputs with chemical fertilizers ensures a balanced nutrient supply throughout the growing season. For instance, the use of controlled-release N fertilizers in conjunction with organic amendments has been shown to significantly improve NUE and reduce N losses (Novair et al., 2021). Field experiments have demonstrated that deep placement of briquetted urea, a form of controlled-release fertilizer, increased grain yields by 21%~23% and improved various NUE metrics compared to traditional broadcast methods (Baral et al., 2020). This integrated approach not only enhances NUE but also promotes sustainable agricultural practices by reducing reliance on chemical fertilizers and mitigating environmental pollution. 5 Microbial and Rhizosphere Interventions for Enhancing NUE 5.1 Role of soil microorganisms Soil bacteria and fungi play a crucial role in influencing nitrogen availability and uptake in rice plants. The rhizosphere, the narrow region of soil influenced by root secretions and associated soil microorganisms, is a hotspot for microbial activity that significantly impacts nitrogen cycling. Soil microorganisms, including bacteria and fungi, contribute to various nitrogen transformations such as ammonification, nitrification, and nitrogen fixation. For instance, the inoculation of rice plants with Azospirillum brasilense and Pseudomonas fluorescens has been shown to enhance ammonification and nitrogenase activities in the rhizosphere, thereby increasing the nitrogen supply capacity and improving rice grain yields (Junhua et al., 2021). Additionally, the application of nitrogen fertilizers can alter the microbial community structure in the rhizosphere, affecting the balance between nitrifying and denitrifying bacteria, which in turn influences nitrogen availability for plant uptake (Chen et al., 2019). Moreover, soil microorganisms can modulate the rhizosphere priming effect (RPE), a phenomenon where root exudates stimulate microbial turnover and the decomposition of soil organic matter, thereby affecting nitrogen dynamics. Nitrogen fertilization has been found to reduce microbial carbon-to-nitrogen (C:N) imbalance and soil pH, which can influence microbial metabolic efficiency and turnover time, ultimately regulating the RPE and nitrogen availability in paddy soils (Chen et al., 2021). These interactions highlight the importance of understanding and managing soil microbial communities to enhance nitrogen use efficiency (NUE) in rice cultivation. 5.2 Inoculants for nitrogen fixation The use of nitrogen-fixing bacteria, such as Azospirillum and Rhizobium, holds significant potential for improving NUE in rice. These bacteria can convert atmospheric nitrogen into a form that plants can readily absorb, reducing the need for chemical nitrogen fertilizers. Inoculation with nitrogen-fixing bacteria like Azospirillum brasilense has been shown to enhance nitrogenase activity in the rhizosphere, particularly under lower nitrogen application rates, thereby contributing to a more sustainable nitrogen supply for rice plants (Junhua et al., 2021). Similarly, Pseudomonas stutzeri A1501 has been demonstrated to improve plant growth and nitrogen content in maize by increasing the population of indigenous diazotrophs and ammonia oxidizers in the rhizosphere (Ke et al., 2019). The application of these inoculants not only enhances nitrogen fixation but also positively influences the overall microbial community structure in the rhizosphere. For example, inoculation with nitrogen-fixing bacteria can lead
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