Maize Genomics and Genetics 2025, Vol.16, No.1, 20-33 http://cropscipublisher.com/index.php/mgg 27 with NPK+hydrolyzed animal epithelium and micronutrients (NPK+Hae+micro) and PK+Ascophyllum nodosum extracts (PK+An) increased root dry biomass and volumetric root length density, leading to a higher number of commercial seeds produced and reduced seed disposal rates (Boscaro et al., 2023). Furthermore, the foliar application of molybdenum (Mo) has been found to enhance photosynthetic metabolism and grain yields in maize. Mo application increased leaf nitrate reductase activity, nitrogen and protein content, Rubisco activity, net photosynthesis, and grain yield, indicating its efficiency in improving nitrogen metabolism and carbon fixation (Oliveira et al., 2022). Similarly, the combined foliar application of iron (Fe) and Mo with nitrogen fertilization improved the shade tolerance of soybean in maize-soybean intercropping systems by enhancing chlorophyll content, photosynthetic activities, and associated enzymatic activities, ultimately leading to better growth and yield (Nasar et al., 2022). These studies underscore the benefits of foliar fertilization as a supplementary strategy to boost maize productivity. 7.3 Promotion of fertigation (combined fertilization and irrigation) and its advantages in high-density planting Fertigation, the combined application of fertilizers and irrigation, offers several advantages in high-density planting of maize. This method ensures the efficient delivery of nutrients directly to the root zone, enhancing nutrient uptake and utilization. A study on the interaction of irrigation management and nitrogen fertilization revealed that controlled-release urea (CRU) combined with optimal irrigation significantly improved maize yield, nitrogen uptake, and growth. Under conventional irrigation, CRU application at 210 and 315 kg N/ha resulted in similar yields, which were significantly higher than those obtained with common urea. In areas with mild water stress, increasing the CRU rate to 315 kg N/ha further improved yield by counteracting the adverse effects of drought (Li et al., 2020). Additionally, the application of nitrogen fertilizer and plant growth regulators in high-density planting has been shown to enhance root-bleeding sap rate, nutrient absorption, and grain yield. The combination of nitrogen application at 200 kg/ha with chemical control improved the delivery rates of amino acids and mineral nutrients in root-bleeding sap, leading to higher phosphorus and potassium uptake and translocation. This treatment also maintained high levels of key enzymatic activities in leaves and grains, ultimately increasing maize yield and quality (Liu et al., 2022). These findings highlight the potential of fertigation to optimize nutrient and water management, thereby improving maize productivity in high-density planting systems. 8 Environmental and Economic Considerations 8.1 Potential environmental impacts of over-fertilization and sustainable management practices Over-fertilization in maize cultivation has significant environmental repercussions, including soil degradation, water pollution, and increased greenhouse gas emissions. Excessive nitrogen (N) fertilization, in particular, has been linked to severe pollution issues, such as nitrate leaching into groundwater and the emission of nitrous oxide, a potent greenhouse gas (Li et al., 2020; Nasar et al., 2021). Studies have shown that the fertilization phase has the most detrimental influence on ecosystems, followed by the harvesting period (Kumar et al., 2022). Sustainable management practices, such as optimizing N application rates and employing N-transformation inhibitors, have been developed to mitigate these impacts. These practices not only improve crop yield and nitrogen use efficiency (NUE) but also reduce N losses, thereby minimizing environmental pollution (Quan et al., 2021). Sustainable management practices also include the use of organic-inorganic fertilizer combinations, which have been shown to significantly increase water use efficiency (WUE) and reduce the environmental footprint of maize production (Shi et al., 2023). For instance, the Nutrient Expert (NE) management system, which combines optimized nutrient management with improved plant density, has demonstrated the potential to sustain maize yields while reducing reactive nitrogen losses and greenhouse gas emissions (Huang et al., 2021). These practices are crucial for achieving climate-smart agricultural production with minimal environmental damage. 8.2 Cost-benefit analysis of different planting density and fertilization combinations The economic benefits of different planting density and fertilization combinations in maize cultivation can vary significantly. For example, a study conducted in northwest China found that the optimal combination of irrigation
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