Molecular Soil Biology 2024, Vol.15, No.4, 163-171 http://bioscipublisher.com/index.php/msb 166 affect NUE. Optimal rates can enhance uptake, while excessive application can lead to nitrogen leaching and reduced efficiency (Akhtar et al., 2023a). Tillage practices, such as rotary tillage and plow tillage, impact root distribution and soil properties, thereby affecting nitrogen uptake (Sui et al., 2020). Mulching with straw can regulate soil temperature and moisture, improving the physiological conditions for nitrogen uptake (Guo et al., 2021; Akhtar et al., 2023a). Nitrogen source and timing, including the type of nitrogen fertilizer and the timing of its application, play a crucial role in how effectively maize plants absorb nitrogen. Split applications and the use of slow-release fertilizers have been shown to improve NUE (Abbasi et al., 2013). 4.3 Measurement techniques Measuring nitrogen uptake efficiency involves several methods, including nitrogen recovery efficiency (NRE), nitrogen use efficiency (NUE), the ¹⁵N tracer technique, and soil and plant analysis. Nitrogen Recovery Efficiency (NRE) measures the proportion of applied nitrogen that is taken up by the plant. It is calculated by comparing the nitrogen content in the plant with the amount of nitrogen applied (Zhang et al., 2020; Meng et al., 2021). Nitrogen Use Efficiency (NUE) is a broader measure that includes both the uptake and utilization of nitrogen by the plant. It is often assessed by evaluating the grain yield per unit of nitrogen applied (Guo et al., 2021; Akhtar et al., 2023a). The ¹⁵N Tracer Technique involves using nitrogen isotopes to trace and quantify the uptake and distribution of nitrogen within the plant and soil system. It provides detailed insights into nitrogen dynamics and efficiency (Lin et al., 2022). Soil and Plant Analysis, through regular sampling and analysis of soil and plant tissues for nitrogen content, helps in monitoring and assessing nitrogen uptake and utilization over the growing season (Lei et al., 2020; Sui et al., 2020). By understanding and optimizing these factors and measurement techniques, farmers and researchers can improve nitrogen uptake efficiency in maize, leading to better crop performance and sustainability. 5 Quality Improvement in Maize 5.1 Indicators of maize quality Maize quality is typically assessed through various indicators, including grain yield, nitrogen use efficiency (NUE), and the biochemical composition of the grain such as starch and soluble sugar content. For instance, the incorporation of straw and nitrogen fertilization has been shown to significantly enhance these quality indicators (Su et al., 2020). In a study conducted in the semi-arid region of China, the combination of full wheat straw mulch and nitrogen fertilization (FS+N) resulted in a 29% increase in grain yield, 9.6% improvement in NUE, and substantial increases in soluble sugar and starch content by 80% and 59%, respectively (Yu et al., 2019; Akhtar et al., 2023a; Hu et al., 2023). 5.2 Effects of nitrogen on grain quality Nitrogen plays a crucial role in improving the grain quality of maize. Adequate nitrogen application enhances photosynthetic efficiency, which in turn boosts grain yield and quality. For example, a study found that nitrogen application at 225 kg/ha significantly improved photosynthetic traits and nitrogen accumulation in grains, leading to higher grain yield and improved nitrogen absorption efficiency (Wang et al., 2022). However, excessive nitrogen application can lead to environmental issues such as nitrate leaching, which underscores the importance of optimizing nitrogen levels (Meng et al., 2021). 5.3 Role of straw and fertilizer interaction The interaction between straw incorporation and nitrogen fertilization has been shown to have a synergistic effect on maize quality. Straw incorporation not only improves soil fertility but also enhances nitrogen uptake and utilization. For instance, a six-year study in Northeast China demonstrated that straw incorporation at higher rates consistently improved soil fertility indices, which in turn elevated grain yield and nitrogen use efficiency over time (Ma et al., 2021). Additionally, the combination of straw incorporation with deep placement of nitrogen fertilizer significantly increased grain yield and nitrogen recovery efficiency in direct-seeded rice, suggesting similar benefits could be expected in maize (Chen et al., 2020). Another study highlighted that straw incorporation coupled with optimized nitrogen fertilization could improve maize yield and nitrogen balance, thereby enhancing overall crop quality (Lei et al., 2020; Wang et al., 2024) (Figure 2).
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