Field Crop 2024, Vol.7, No.5, 278-286 http://cropscipublisher.com/index.php/fc 280 3 Agronomic Biofortification: Concept and Approaches Agronomic biofortification is a sustainable agricultural strategy aimed at increasing the concentration of essential micronutrients in crops through various agronomic practices. This approach is particularly significant in addressing micronutrient deficiencies, often referred to as “hidden hunger”, which affect a large portion of the global population, especially in developing countries (Dhaliwal et al., 2022b). 3.1 Definition and principles of agronomic biofortification Agronomic biofortification involves the application of mineral fertilizers to the soil or directly to the plant leaves (foliar application) to enhance the nutrient content of crops. The primary principle behind this approach is to increase the bioavailability of essential micronutrients such as zinc (Zn), iron (Fe), and selenium (Se) in the edible parts of the plant, thereby improving the nutritional quality of the food produced (Dhaliwal et al., 2022a). This method is considered a quick and cost-effective solution to improve crop nutrient content and is particularly useful in regions where soil nutrient deficiencies are prevalent. 3.2 Overview of strategies for biofortifying maize Several strategies are employed to biofortify maize, a staple crop for many populations worldwide. These strategies include soil amendment, foliar application, and the use of advanced fertilizers such as chelated and nano-fertilizers. Soil amendment involves the addition of micronutrient-rich fertilizers to the soil, which enhances the nutrient uptake by maize plants. Foliar application, on the other hand, involves spraying nutrient solutions directly onto the leaves, allowing for quicker absorption and utilization by the plant (Bhardwaj et al., 2022). Additionally, the use of plant growth-promoting rhizobacteria (PGPR) has shown promise in enhancing the bioavailability of nutrients like Zn and Fe in maize, further improving its nutritional quality (Ahmad et al., 2023). 3.3 Genetic enhancement versus agronomic biofortification: comparative analysis While both genetic enhancement and agronomic biofortification aim to increase the nutrient content of crops, they differ in their approaches and outcomes. Genetic enhancement involves the breeding of crop varieties with higher nutrient content through conventional breeding or transgenic techniques. This method provides a long-term solution but requires significant time and resources to develop and commercialize nutrient-rich varieties (Bouis and Welch, 2010; Garg et al., 2018). In contrast, agronomic biofortification offers a more immediate solution by directly supplying nutrients to the plants through soil and foliar applications. This method can be quickly implemented and adjusted based on the specific nutrient deficiencies of the soil and crop (Avnee et al., 2023). However, genetic enhancement has the advantage of being a one-time investment that can provide sustained benefits over multiple growing seasons, whereas agronomic biofortification may require repeated applications of fertilizers. Additionally, genetically enhanced crops can be bred to possess multiple beneficial traits, such as increased resistance to pests and diseases, alongside improved nutrient content (Goredema-Matongera et al., 2021). Despite these differences, both approaches are complementary and can be integrated to achieve the best outcomes in combating micronutrient deficiencies and improving global nutritional security (Nuss and Tanumihardjo, 2010; Kiran et al., 2022). 4 Methods for Enhancing Micronutrient Content in Maize 4.1 Soil-based approaches (e.g., micronutrient fertilization, soil amendment) Soil-based approaches for enhancing micronutrient content in maize primarily involve the application of micronutrient fertilizers and soil amendments. These methods are effective in addressing deficiencies in essential nutrients such as zinc (Zn), iron (Fe), and selenium (Se). For instance, the application of zinc sulfate to soil has been shown to increase Zn concentration in crops like cabbage and canola (Mao et al., 2014). Similarly, nitrogen fertilization can improve the uptake of Zn and Fe in maize, enhancing the overall nutritional quality of the crop (Grujcic et al., 2021). Soil amendments, including the use of chelated fertilizers and nanoparticles, have also been found to improve nutrient uptake efficiency and translocation to consumable parts of the plant (Figure 2). The study of Bhardwaj et al. (2022) illustrates a holistic approach to agronomic biofortification, integrating crop improvement, soil management, fertilizer management, and agronomic practices. Strategies such as enhancing
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