Research Articles Can agronomic biofortification boost nutrition in maize?

Maize is the second largest crop of the world after wheat, but the most produced globally in terms of total volume, with 1.2 billion tons annually. Along with wheat and rice, these staple cereals represent near half of world’s food calories, especially in developing countries. Its importance as a source of food and income is not in question, but its potential to nourish better is an exciting field of study for many agronomy and nutrition researchers worldwide. 

Zinc (Zn) and iron (Fe), two main micronutrients that are fundamental for human development are naturally present in maize grain, but not at the levels that can fulfill nutritional requirements. Biofortification is one of the key strategies to offset low levels of Zn and Fe in maize grain. However, this is not the only strategy to consider. Agronomical practices such as fertilizers inputs and soil health are also critical variables that directly affects not only yields, but the levels of those micronutrients and therefore, consequences on poor health, stunted growth, and economic losses. 

A comprehensive review paper Maize-grain zinc and iron concentrations as influenced by agronomic management and biophysical factors: a meta-analysis, published recently in the prestigious journal Food Security addresses these issues by analyzing the factors influencing Zn and Fe concentrations in maize grain. The study aimed to establish the global distribution of Zn and Fe concentrations in maize grain, by assessing the effectiveness of different agronomic practices, particularly the use of Zn fertilizers, in increasing maize grain yields and Zn and Fe levels. It also aimed to identify key biophysical factors that could guide agronomic biofortification efforts. 

For the first time, the distributions and the expected values of Zn and Fe concentrations in maize grain at the global level are provided at the highest level of accuracy, based on available literature: Using 5,874 data points from 138 published papers across 34 countries, the researchers estimated that there is a 7.5% probability of maize grain-Zn concentrations exceeding the benchmark target of 38 mg/kg. For grain-Fe concentrations, 3,187 data points from 65 studies across 27 countries showed an estimation of 8.5% probability of exceeding the target of 60 mg/kg. The meta-analysis, which included 70 papers, revealed that applying Zn and/or Fe in combination with inorganic NPK (nitrogen, phosphorous and potassium) fertilizer can significantly increase maize grain-Zn and Fe concentrations by 31% compared to the control (NPK only). 

The study also highlighted several key findings, like higher soil organic matter and optimal pH levels improve nutrient availability and uptake by plants; Applying Zn, particularly through combined soil and foliar applications, was found to be most effective in increasing grain-Zn and Fe concentrations,while the application of organic inputs, such as manure and crop residues, significantly increased grain Zn and Fe levels.  

Despite these insights, the study identified significant data gaps and limitations: For instance, there is a lack of data on other micronutrients like selenium (Se) and antinutritional factors such as phytate, which affects Zn bioavailability. On the other hand, the optimal Zn concentration in soil for increasing grain-Zn concentration may differ from the concentration required for high yields, highlighting the need for more research.  Agronomic biofortification could provide a solution to nutritional deficiencies, but more information is needed in this area. The research has revealed regional imbalances in the representativeness of studies , with most research conducted in India and Pakistan and limited representation from Africa. 

The study recommends routine measurement and reporting of grain-Zn and Fe content and the standardization of research protocols to capture produce quality data in agronomy and breeding programs. It also emphasizes the importance of monitoring long-term changes in Zn and Fe concentrations in grain and soil. Also, the findings of this meta-analysis have significant implications for national fertilizer recommendations and agricultural policies: The potential of Zn-enriched fertilizers to alleviate human dietary Zn deficiency highlights the need for policies that support the use of these fertilizers. Additionally, the study underscores the importance of optimizing nutrient management to improve Zn and Fe concentrations in maize grain. 

To unlock the full potential of maize as a nutritional powerhouse, a collaborative approach is essential. Farmers, researchers, policymakers, and the private sector must work together to implement sustainable and effective strategies. Key recommendations include Investing in research to deepen our understanding of the complex factors influencing maize nutrient content; Disseminating knowledge about optimal agronomic practices to farmers, encouraging the development of nutrient-rich maize varieties and innovative farming technologies and building robust food systems that ensure the production, distribution, and consumption of nutrient-rich foods. A concerted effort in research and policy to optimize nutrient management and improve crop micronutrient content is needed, thereby enhancing global food security and public health. 

Read the paper: Maize-grain zinc and iron concentrations as influenced by agronomic management and biophysical factors: a meta-analysis

This study was supported  various donors through the CGIAR Trust Fund in relation to the CGIAR Initiative Excellence in Agronomy (EiA), and It included the participation of researchers from Addis Ababa University and the CGIAR centers Alliance of Bioversity & CIAT, AfricaRIce, ICARDA and IRRI. Job Kihara, Principal scientist of the Alliance is the corresponding author. Job also leads the Agronomic Biofortification community of practice of the CGIAR.