Technological Innovations in Agronomic Iron Biofortification: A Review of Rice and Bean Production Systems in Brazil

Abstract

Iron deficiency is a widespread public health concern, particularly in regions where rice (Oryza sativa) and beans (Phaseolus spp.) are staple foods with naturally low bioavailable iron content. Agronomic biofortification is a practical strategy to increase micronutrient levels in crops through soil, foliar, and seed-based fertilization techniques. This review synthesizes scientific studies published between 2014 and 2024 that evaluated the effectiveness of agronomic iron biofortification methods in rice and beans. The results demonstrate that site-specific interventions, such as the selection of iron sources and application methods, can improve iron concentration in grains and contribute to more nutritious and resilient food systems. However, challenges remain. There is limited information about human iron bioavailability, and the response to fertilization varies depending on soil and environmental conditions. To address these gaps, future research should include bioavailability assessments and field validation. Even so, integrating iron biofortification into standard fertilization practices is a promising approach to improve food quality and combat hidden hunger in vulnerable populations.

1. Introduction

Rice (Oryza sativa) and beans (Phaseolus spp.) are staple foods consumed daily by millions of people, particularly in Latin America, Asia, and Africa. In Brazil, this combination is deeply embedded in the national diet across all socioeconomic strata [1,2]. These crops are critical not only for caloric intake but also as primary sources of plant protein, carbohydrates, and dietary fiber. However, they are naturally low in bioavailable iron (Fe), which is a key limiting factor in efforts to improve nutritional security through staple-based diets [3].

Globally, iron deficiency remains a major public health concern, affecting an estimated 2.2 billion people and resulting in iron deficiency anemia in over 1.6 billion individuals, especially among women and children [4,5]. The consequences are severe and include impaired cognitive development, reduced physical capacity, increased maternal and infant mortality, and diminished economic productivity [6,7]. In addition to dietary limitations, the prevalence of iron deficiency is exacerbated by factors such as soil degradation, nutrient-depleted cropping systems, and reliance on low-diversity food sources, particularly in regions marked by poverty and food insecurity [8,9].

To address these challenges, sustainable agricultural innovations are essential. Engineering-based approaches, such as fertigation, controlled-release fertilizers, or chelated iron formulations, enhance the efficiency of iron uptake while reducing environmental loss. Among them, agronomic biofortification has emerged as a viable solution to increase the concentration of micronutrients—such as iron—in staple crops by applying mineral fertilizers through soil, foliar, or seed-based methods [10]. Unlike genetic modification or conventional breeding, agronomic biofortification offers rapid implementation and compatibility with local farming practices, while promoting more efficient nutrient cycling and soil–plant interactions [11,12].

From an environmental perspective, agronomic biofortification is not merely a nutritional intervention, it also intersects with broader sustainability goals. The success of these strategies depends heavily on soil properties, pH, organic matter content, and the management of edaphoclimatic conditions that govern iron solubility, availability, and plant uptake [13,14]. Thus, the integration of biofortification practices into sustainable soil management plans can improve both crop nutrition and soil health, contributing to long-term agroecosystem resilience. Agronomic biofortification lies at the intersection of plant science, soil health, public health, and sustainability, making it a compelling transdisciplinary solution for the challenges of food and nutrition security in the Anthropocene [10,15,16].

Despite the promising outcomes of agronomic iron biofortification reported in experimental studies, critical challenges remain. Variability in results due to soil conditions, interactions with other nutrients (e.g., phosphorus, manganese, and nickel), and limited translocation of iron to grains highlight the need for site-specific management and interdisciplinary approaches [17,18,19,20]. Moreover, while numerous studies report increased iron content in plant tissues, relatively few evaluate the bioavailability of iron to human consumers, which is essential for the success of public-health-oriented strategies [21,22,23,24,25,26].

Considering the importance of rice and beans in the diet, especially in vulnerable populations, this review analyzes studies from 2014 to 2024 on agronomic biofortification with iron in rice and beans, addressing methods used, interactions with the soil and environment, and impacts on sustainable production and nutritional security. Agronomic biofortification contributes to the United Nations Sustainable Development Goals (SDGs) by enhancing micronutrients in crops and encouraging sustainable soil management, addressing SDGs 2, 3, 12, and 15, promoting more resilient, inclusive and balanced agroecosystems.

2. Methodology of Data Collection

This literature review was conducted based on searches in three academic databases: PubMed, Google Scholar, and Scopus. The search strategy used the same keywords across all platforms: “Rice and bean biofortification with iron.” The searches were limited to scientific articles published from 2014 to 2024.

The inclusion criteria focused on original research articles that investigated iron biofortification in Oryza sativa (rice) and Phaseolus spp. (beans), specifically using agronomic methods. The exclusion criteria were studies involving non-plant organisms (e.g., fungi or animals), studies on plant species other than rice and beans, review articles, and studies for which full-text access was not available.

All retrieved articles were independently screened and evaluated by four reviewers. In cases of disagreement, decisions were reached through consensus. The main factors identified as influencing the effectiveness of iron biofortification in rice and bean crops were the genetic material of the plant, the dosage of the applied fertilizer, the chemical form of iron used, and the application method. This review followed the guidelines outlined in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) protocol [27].

3. Results and Discussion

3.1. Selection and Characterization of Studies

A comprehensive literature search was conducted across four major databases, Scopus, PubMed and Google Scholar, using the unified search term “Rice and bean biofortification with iron”. The review covered the period from 2014 to 2024 and focused exclusively on original research articles addressing iron biofortification in Oryza sativa and Phaseolus spp. via agronomic practices.

An initial pool of 107 records was identified: 48 from Scopus, 9 from PubMed, and 50 from Google Scholar. After removing duplicates, 75 articles remained. These were subjected to a rigorous screening process, with inclusion criteria emphasizing experimental studies employing soil, foliar, seed-based, or nutrient solution fertilization. Exclusion criteria involved studies focusing on genetic modification, non-target crops, review articles, or unavailable full texts. Following this process, 17 articles were retained for full review and synthesis. The selection process is detailed in the PRISMA flowchart (Figure 1).

While the number of eligible studies was relatively limited, their geographic and methodological diversity provided valuable insights into how site-specific agronomic interventions affect iron uptake and bioavailability in staple crops. Nevertheless, it is important to acknowledge that many studies lacked comprehensive soil characterization or did not assess human iron bioavailability, which are critical components for translating agronomic findings into nutritional and environmental outcomes.

The methodological rigor applied in this review, in accordance with the PRISMA 2020 guidelines, ensures transparency and reproducibility of study selection. However, the limited number of long-term field studies and the scarcity of interdisciplinary approaches underscore a critical gap in the literature, particularly in linking agronomic biofortification to ecosystem services and public health impacts. These gaps provide direction for future research seeking to enhance the resilience and sustainability of cropping systems through micronutrient-enriched agriculture.

3.2. Iron and Anemia in the Global Population

The articles selected from the databases provided information on food insecurity, the impact of iron deficiency on low-income populations, and the role of biofortification in supporting these groups. The global population has recently reached 8.2 billion people, and projections from population control agencies estimate that in 30 to 40 years this number will exceed 9 billion. With continued population growth, food and nutritional insecurity is becoming progressively more prevalent, particularly in developing countries, where severe socioeconomic deprivation and hunger persist due to inequitable resource distribution. Food insecurity results, among other factors, from malnutrition and the lack of access to healthy diets by a large portion of low-income populations [8].

Iron is a nutrient of vital importance for human health [19]. Iron, zinc (Zn), and vitamin A are essential nutrients in the human diet, and when not consumed in adequate amounts to meet physiological needs, they may cause various health disorders [8]. According to data from the World Health Organization (WHO), micronutrient deficiency—also referred to as hidden hunger—affects approximately 2.2 billion people globally, representing around 30% of the world’s population [4].

Anemia affects approximately 1.6 billion individuals worldwide [5] (Figure 2). WHO data indicate that the most affected groups include women (42% of pregnant women), children aged 0 to 5 years, and men over the age of 15 [6]. Iron deficiency anemia can significantly reduce quality of life by impairing cognitive function, learning capacity, physical development, and work productivity [7]. In children, chronic iron deficiency is a major contributor to stunted growth, a condition characterized by low height-for-age and associated with long-term developmental delays. Approximately 161 million children under the age of five worldwide are affected by stunting [28]. This condition is often linked to diets poor in bioavailable iron, such as those based primarily on rice and beans, without proper nutritional enhancement.

This high prevalence of anemia, particularly iron deficiency anemia, is primarily explained by three underlying factors: increased physiological demand for iron, as occurs during pregnancy; insufficient or inadequate dietary intake; and poor iron absorption by the human body [4]. According to the analyzed studies, food biofortification is one of the strategies currently employed to reduce nutrient deficiencies. However, to be effectively targeted at low-income populations, it is essential that biofortification be implemented in staple and affordable foods for this segment of the population, such as beans and rice [8].

Beyond its well-documented public health implications, iron deficiency also reflects deeper structural weaknesses in the food and agricultural systems. The persistence of anemia in vulnerable populations underscores the urgent need to redesign cropping systems that not only ensure caloric sufficiency but also deliver essential micronutrients through sustainable means [30,31,32]. Agronomic iron biofortification presents a critical opportunity to strengthen the nutritional resilience of agroecosystems, especially when aligned with soil health restoration practices. Iron uptake and translocation in crops are highly dependent on soil properties such as pH, organic matter, microbial activity, and nutrient interactions. Therefore, interventions aimed at enhancing iron bioavailability must be integrated into broader strategies of sustainable soil management, such as the use of organic amendments, precision fertilization, and agroecological practices.

3.3. Importance of Beans and Rice in the Diet

Common beans are a dietary staple in many populations and are rich in minerals, carbohydrates, and folic acid and serve as an important source of iron [33]. Beans are widely cultivated and consumed across the globe, particularly in African and Latin American countries [34]. The average daily consumption in these regions ranges from 100 to 180 g per person [34].

Between 2015 and 2017, global bean production reached approximately 28.5 million tons. Of this total, only 13% was traded internationally, with the majority being consumed domestically in the producing countries [1]. Similarly, rice plays a central role in global diets and is currently the most consumed cereal crop worldwide. However, despite its high consumption, polished rice contains low levels of iron [33], which makes it a key target for agronomic biofortification. During the same period, global rice production averaged 757 million tons, with only 8% of this volume being exported [1]. The joint consumption of rice and beans is common in many cultures and has nutritional benefits, as these two staples provide complementary amino acid profiles. While each alone is deficient in certain essential amino acids, their combination improves protein quality and contributes to a more balanced diet [1].

The central role of beans and rice in global diets makes them strategic vehicles for nutrition-sensitive agricultural interventions. However, their contribution to food security must go beyond energy provision to include adequate micronutrient supply. Enhancing the nutritional profile of these crops through agronomic biofortification directly contributes to strengthening dietary quality in low-income populations, while reducing reliance on costly dietary supplements or industrial fortification programs [19,35,36]. From an environmental perspective, the large-scale cultivation of rice and beans offers a unique opportunity to embed sustainable soil and nutrient management practices into food systems. Iron biofortification strategies—particularly those involving soil and foliar fertilization—can be designed to work synergistically with practices that restore soil organic matter, enhance microbial activity, and reduce nutrient runoff, thus reinforcing agroecosystem health [37,38,39].

Integrating nutrient-enrichment goals with agroecological principles ensures that the intensification of rice and bean production does not compromise long-term soil fertility or environmental quality. As staple crops with high cultural, economic, and nutritional value, beans and rice represent ideal platforms for advancing agricultural sustainability agendas while addressing critical public health challenges.

3.4. Agronomic Technologies for Iron Biofortification

All studies cited in

Table 1. The impact of iron application methods and strategies on the biofortification of rice and beans.

Reference	Plant	Long-Term Study	Biofortification Method	Application Technique	Effect
(Dias et al., 2015) [22]	Rice and bean	No	Conventional plant breeding	Not applicable	Increased Fe * bioavailability and antioxidant capacity
(Gupta et al., 2023) [40]	Rice	Yes	Genetic engineering	Genetic transformation	Increased Fe content
(Petry et al., 2014) [34]	Bean	No	Conventional plant breeding	Not applicable	Increased Fe concentration and absorption
(Junqueira-Franco et al., 2018) [23]	Bean	No	Conventional plant breeding	Not applicable	No increase in Fe content
(Yousefi et al., 2023) [41]	Beans	No	Agronomic practices	Foliar application	Increased yield and Fe concentration
(Corrêa et al., 2020) [42]	Cowpea	No	Agronomic practices	Management of biofortified plants	Increased Fe bioavailability
(Liu et al., 2016) [43]	Bean	No	Genetic engineering and agronomic practices	Molecular genetics and hydroponics	Improved Fe absorption and availability
(Binagwa et al., 2020) [44]	Bean	No	Agronomic practices	Soil application	Increased Fe bioavailability
(Zulfiqar et al., 2021) [11]	Rice	No	Agronomic practices	Seed treatment, Fe osmopriming, surface broadcasting, and foliar application	Increased productivity and Fe bioavailability
(De la Cruz Lázaro et al., 2024) [45]	Bean	No	Agronomic practices	Foliar application	Increased Fe bioavailability
(Ramzani et al., 2016) [17]	Rice	No	Agronomic practices	Soil application	Improved plant growth, physiology, rice yield, and nutritional value of the grains
(Patel et al., 2018) [46]	Bean	No	Agronomic practices	Seed treatment	Increased vegetative parameters, Fe content, protein, and carbohydrates
(Márquez-Quiroz et al., 2015) [47]	Bean	No	Agronomic practices	Nutrient solution application	Increased productivity and Fe bioavailability
(Fageria and Santos, 2014) [48]	Rice	No	Agronomic practices	Soil application	Increased yield and Fe concentration
(Trijatmiko et al., 2016) [49]	Rice	No	Genetic engineering	Transgenesis	Increased Fe concentration without compromising productivity
(Prom-U-Thai et al., 2020) [50]	Rice	Yes	Agronomic practices	Foliar application	There were no statistical differences depending on the application of Fe
(Felix et al., 2021) [51]	Bean	No	Agronomic practices	Soil and foliar application	It increased Fe concentrations in the grains, as well as levels of ash, fat, protein, crude fiber, total phenols, and anthocyanins, while decreasing carbohydrate content and energy

* Fe: iron.

investigated iron biofortification in rice and/or bean crops. A significant number of these studies focused on agronomic practices as the primary method, including soil fertilization, foliar application, or the management of pre-biofortified cultivars. Most experiments were short-term and limited to a single growing cycle. Across the studies, agronomic interventions generally led to increased iron bioavailability in grains, and some also reported improvements in crop productivity.

Recent studies in plant molecular physiology emphasize that the success of agronomic biofortification depends not only on the iron source or application method, but also on the plant’s intrinsic regulatory capacity to absorb, allocate, and store iron. As highlighted by Kroh and Pilon (2019) [52], the transcription factor ILR3 (bHLH105) plays a dual role in iron homeostasis, simultaneously activating root iron uptake and repressing ferritin gene expression under deficiency conditions. This coordination ensures that iron is directed toward vital cellular functions—such as chloroplast activity—while minimizing oxidative stress.

Furthermore, the systemic regulation of iron involves signaling peptides (FEP/IMA), membrane transporters (OPT3, YSL1/3), and ubiquitin ligases (BTS/BTSL) that modulate transcriptional responses based on the plant’s iron status. These findings underscore that agronomic interventions must be aligned with the plant’s physiological mechanisms to ensure effective uptake and translocation of iron to edible tissues. Therefore, understanding the molecular networks that control iron homeostasis is essential to enhance the efficiency and sustainability of iron biofortification strategies in rice and beans [53,54,55].

Biofortification is the process of increasing the content and availability of essential micronutrients, such as minerals and vitamins, in staple food crops intended for human nutrition [56]. This can be achieved through three main approaches: conventional plant breeding, agronomic practices, and genetic engineering in crop improvement [10] (Figure 3).

Among these approaches, agronomic biofortification stands out for its practicality, cost-effectiveness, and ability to deliver results within a single growing season, without requiring genetic modification [10,12]. Additionally, iron-containing fertilizers can be easily adapted to diverse cultivation conditions and specific plant needs. These advantages likely explain why several of the studies analyzed opted for agronomic practices as the primary method of iron biofortification.

This approach includes various techniques, such as soil fertilization, seed treatment, foliar nutrient application, and complementary practices like inoculation with mycorrhizal fungi, crop rotation, and controlled irrigation [57]. Among these techniques, the application of iron-containing fertilizers—either through soil or foliar routes—is one of the most common and effective strategies. However, the efficiency of this practice may vary depending on soil type, fertilizer formulation, and application method [58].

Among the different application routes, soil fertilization is the most widely adopted technique, especially when higher nutrient inputs are required. In contrast, foliar application is often preferred in situations where nutrient deficiency symptoms are already visible or when the goal is to enhance micronutrient content directly in the edible parts of the plant, particularly when the minerals are not effectively translocated or accumulated [14].

According to the data presented in Table 1, among the studies that adopted agronomic practices, some opted for soil application, likely due to the low native nutrient availability in the experimental soils. In contrast, foliar application demonstrated effectiveness [41], which was reported as increased iron bioavailability in common bean grains. Additionally, studies that applied iron via seed treatment also observed positive results [11,46], as detailed in Table 1.

Agronomic biofortification with iron requires specific considerations due to the limited mobility of this nutrient within plant tissues. The use of metal chelating agents in fertilizers has shown potential to improve iron uptake and translocation [41,43]. Various iron sources, such as FeSO₄·7H₂O, Fe-EDTA, Fe-EDDHA, and Fe nanoparticles, have also been extensively used as fertilizers in rice and bean crops [19,23,42].

Nevertheless, the application of iron must be carried out with caution, as excessive levels may impair plant growth and cause adverse environmental impacts [14]. This risk is particularly elevated in acidic soils, where iron availability is already naturally high [19].

To better understand these risks, it is important to consider the optimal concentration ranges of Fe²⁺ ions in the soil. For most plants, the suitable range varies from 5.6 to 300 ppm throughout the development cycle. Concentrations above 300 ppm may induce toxicity, while levels below 60 ppm are considered insufficient to meet the plant’s nutritional demands and may lead to deficiency symptoms [13].

These critical values are particularly relevant in rice cultivation areas, where iron toxicity is commonly observed and is generally associated with conditions such as poor drainage, highly reducing environments, and elevated sulfide levels [19]. Iron availability is influenced by soil pH, redox potential, water saturation, and aeration status. Poorly drained and waterlogged soils tend to reduce iron to its ferrous form (Fe²⁺), which can reach toxic concentrations above 300 ppm, especially in acid sulfate soils with pH values below 5. In contrast, in well-drained and aerated soils, Fe²⁺ is rapidly oxidized to Fe³⁺, a form that is less available for plant uptake.

Moreover, soil organic matter and microbial activity can influence iron mobilization, as microorganisms facilitate the reduction of Fe³⁺ to Fe²⁺ [13]. Therefore, agronomic practices such as maintaining effective drainage systems, correcting soil pH, and managing organic matter are of critical importance in the iron biofortification process. However, among the articles reviewed on iron biofortification in rice and beans, these factors were not consistently addressed. Only the issue of soil pH maintenance was adequately discussed [17].

The success of agronomic biofortification strategies is intricately tied to the sustainability of soil management practices [10,15,16]. The choice of iron source, application method, and timing must consider not only agronomic efficiency, but also the potential impacts on soil chemical balance, biological activity, and long-term fertility. For instance, the repeated application of synthetic iron fertilizers without regard to soil buffering capacity may lead to nutrient imbalances or even toxicity in sensitive environments, particularly in acidic or poorly drained soils [17,36,59]. To maximize both effectiveness and sustainability, site-specific fertilization protocols should be integrated into broader nutrient cycling strategies that account for organic matter management, microbial support, pH correction, and nutrient interaction [60]. Such integration reinforces the dual function of agronomic biofortification: improving crop nutritional quality while enhancing soil functionality and ecosystem services.

Moreover, foliar application, while efficient for nutrient delivery to edible tissues, should be aligned with environmental safeguards to minimize drift and waste. Similarly, seed treatments and fertigation systems offer the potential for precise and environmentally responsible nutrient delivery, particularly when combined with conservation agriculture techniques.

Although the data in Table 1 demonstrate the positive effects of agronomic interventions, a critical evaluation indicates limitations in the experimental design of the analyzed studies. Most consisted of short-term experiments, often limited to a single growing cycle and conducted under controlled or semi-controlled environments, such as greenhouses or pots. Furthermore, many studies did not include detailed soil characterization, such as pH, organic matter content, or nutrient concentrations, which are fundamental aspects for interpreting the efficiency of iron uptake. The absence of field validation limits applicability under real agricultural conditions, where soil heterogeneity and environmental variability influence nutrient dynamics. Therefore, it is important that studies prioritize long-term, field-based trials that include soil analyses in order to strengthen the validity and practical relevance of agronomic iron biofortification strategies.

3.5. Technical Performance of Iron Biofortification Strategies

Among the various management strategies aimed at improving iron biofortification, the reviewed articles demonstrated that agronomic iron biofortification in rice and beans has yielded positive outcomes, regardless of the cultivation region (

Table 2. Effectiveness of the iron biofortification strategies in rice and beans across different countries.

Reference	Plant	Biofortification Level (%)	Country
(Yousefi et al., 2023) [41]	Bean	22	Iran
(Corrêa et al., 2020) [42]	Bean	29	Brazil
(Liu et al., 2016) [43]	Bean	31	China
(Binagwa et al., 2020) [44]	Bean	60	Africa
(Zulfiqar et al., 2021) [11]	Rice	37	Pakistan
(De la Cruz Lázaro et al., 2024) [45]	Bean	76	Mexico
(Ramzani et al., 2016) [17]	Rice	60	Pakistan
(Patel et al., 2018) [46]	Bean	34	India
(Márquez-Quiroz et al., 2015) [47]	Bean	29	Mexico
(Fageria and Santos, 2014) [48]	Rice	27	Brazil
(Trijatmiko et al., 2016) [49]	Rice	60	The Philippines and Colombia
(Felix et al., 2021) [51]	Bean	40	Mexico

).

It is worth noting that although 17 studies were included in the review, only a subset of them provided sufficient data to be included in Table 2, which is limited to articles that presented clear information on the effectiveness of the iron biofortification strategies.

The process of nutrient translocation from soil to plant, and subsequently to human consumption, is complex and intrinsically related to the bioavailability of iron. Several factors influence the effectiveness of biofortification strategies, as nutrient losses may occur at each transition: from soil to plant, from plant to food, and finally from food to human metabolism. For biofortification to be successful, iron must be available for plant uptake and effectively mobilized into the harvested grains. Additionally, the bioavailability of iron in food products and the health status of individuals significantly influence the final absorption and utilization of iron, ultimately determining the nutritional impact of biofortified crops [19].

Iron uptake by plant roots is a critical step in the biofortification process. Efficient root absorption can follow two main strategies: the reduction strategy (Strategy I) and the chelation strategy (Strategy II) (Figure 4). In Strategy I, proton-ATPases are excreted into the rhizosphere, lowering the pH of the soil and enhancing the solubility of Fe³⁺ ions, facilitating their uptake by plant roots. Ferric-chelate reductases dependent on NADPH convert Fe³⁺ to Fe²⁺, which is then transported across the epidermal plasma membrane by ZIP family transporters, such as IRT1. In contrast, iron uptake in grasses primarily follows Strategy II, which involves four key steps: (1) biosynthesis of mugineic acid family phytosiderophores; (2) release of the phytosiderophores into the rhizosphere; (3) solubilization and chelation of iron by phytosiderophores; and (4) uptake of Fe³⁺–phytosiderophore complexes into the plant. Rice is capable of using both strategies, absorbing both Fe²⁺ and Fe³⁺–phytosiderophore complexes. However, unlike beans, rice lacks the ability to reduce Fe³⁺ to Fe²⁺, thus it depends predominantly on chelation-based uptake [61].

Multiple factors affect iron uptake by plants. One is the excessive application of phosphorus (p), which can interfere with iron absorption due to the chemical affinity between these elements [62,63,64]. Under high ionic solubility conditions, p can precipitate as iron phosphate, reducing iron availability in the soil solution and its uptake by plants [65]. Additionally, manganese (Mn) interacts with iron in acidic soils, where high Mn concentrations can induce iron deficiency. Agricultural practices, such as liming, that raise the soil pH can also limit iron solubility, as iron solubility increases by approximately 1000-fold with each unit decrease in pH [18]. To address iron deficiencies, foliar application of iron sulfate (FeSO₄) or iron chelates (e.g., Fe-EDTA, Fe-EDPA) is recommended. Soil application may also be suitable depending on specific cultivation conditions and soil characteristics [8].

A strategy to enhance iron biofortification is organic matter management in soils [66]. Soils with low organic matter content often exhibit iron deficiency, as humic substances aid in releasing iron ions into the soil solution and contain phenolic groups that facilitate the reduction of Fe³⁺ to Fe^2+. These reduced forms of iron can remain in the soil solution or be adsorbed to exchange sites, increasing iron availability to plants. Moreover, amino acids and fulvic acids may complex iron, preventing its precipitation and thus preserving its solubility [19].

Another promising approach involves beneficial soil microorganisms, known as plant-growth-promoting rhizobacteria (PGPR), which may enhance the effectiveness of biofortification strategies. Certain strains, such as Bacillus subtilis GB03 and Paenibacillus polymyxa BFKC01, have shown potential to improve iron uptake by increasing nutrient availability and mobilization in the soil [18]. However, none of the articles analyzed on iron biofortification in rice and beans addressed the microbial aspect.

While the reviewed studies demonstrate significant increases in iron accumulation across diverse environments, true effectiveness must also account for ecological, nutritional, and social dimensions. The variability observed among countries and cultivars indicates that local soil conditions, climate, and management practices play a decisive role in biofortification success [24,67,68]. This reinforces the importance of regionally adapted strategies that optimize not only yield and nutrient density, but also environmental integrity. Moreover, enhancing nutrient concentrations in grains must be complemented by actions that safeguard soil health and biodiversity, particularly in systems already facing degradation or input intensification.

The development and dissemination of biofortified cultivars should occur within frameworks that promote low-impact fertilization, integrated pest management, organic amendments, and water-use efficiency. These approaches ensure that the benefits of iron biofortification are achieved without compromising the ecological sustainability of production systems. In addition to agronomic efficiency, the nutritional and social effectiveness of biofortification depends on crop accessibility, cultural acceptance, and equitable distribution, particularly in rural and food-insecure communities [69,70]. Therefore, biofortification should be embedded within inclusive agricultural policies and public health programs that prioritize food sovereignty and nutrition-sensitive value chains.

3.6. Iron Delivery Technologies in Biofortification

Based on the selected articles, studies on iron biofortification in plants can only be considered complete when they include analyses of the nutrient’s bioavailability in the human body [22], emphasizing that an increase in iron concentration in plants does not necessarily translate to greater absorption in humans, as iron metabolism in plants and humans follows different mechanisms. Similar findings were reported by [23], who found no significant differences in iron absorption between individuals who consumed common beans and those who consumed iron-biofortified beans.

The reviewed studies evaluated different iron sources, with a particular focus on ferrous sulfate and iron chelates, as summarized in

Table 3. Iron forms evaluated in studies on biofortified rice and bean plants.

Reference	Plant	Iron form Evaluated	Impact on Nutritional Quality
(Junqueira-Franco et al., 2018) [23]	Bean	Ferrous sulfate	No significant effect
(Dias et al., 2015) [22]	Rice and bean	Ferrous sulfate	Increases
(Yousefi et al., 2023) [41]	Bean	Iron chelate	Increases
(Liu et al., 2016) [43]	Bean	Iron chelate	Increases
(Corrêa et al., 2020) [42]	Cowpea	Ferrous sulfate	Increases
(Márquez-Quiroz et al., 2015) [47]	Bean	Iron chelate and ferrous sulfate	Increases
(De la Cruz Lázaro et al., 2024) [45]	Bean	Iron chelate and ferrous sulfate	Increases
(Zulfiqar et al., 2021) [11]	Rice	Ferrous sulfate	Increases
(Ramzani et al., 2016) [17]	Rice	Ferrous sulfate	Increases
(Prom-U-Thai et al., 2020) [50]	Rice	micronutrient cocktail solution	No significant effect
(Felix et al., 2021) [51]	Bean	Iron chelate and ferrous sulfate	Increases

. These studies generally reported positive effects on iron content or bioavailability in grains [41,42,43]. However, only two studies directly assessed iron absorption in humans, and both found little or no significant improvement [22,23].

The main iron forms investigated across the studies were ferrous sulfate and iron chelates, either applied individually or in combination (3). This reflects the common use of these compounds in agronomic biofortification programs due to their relative availability and effectiveness.

Some authors have assessed iron absorption efficiency in the human body through ferritin quantification, which is a protein responsible for storing iron in human cells [61]. In this context, within an optimal diet, the consumption of iron-biofortified rice and beans should be accompanied by foods rich in carotenoids and vitamin A—such as pumpkin and sweet potatoes—which enhance the expression of genes involved in iron metabolism, thereby improving iron bioavailability and absorption in the human body [22].

The chemical form of iron used in biofortification programs is a key factor in nutrient uptake and grain enrichment, but it also affects soil chemistry, environmental safety, and economic feasibility. Compounds such as ferrous sulfate and synthetic chelates (Fe-EDTA, Fe-EDDHA) should be assessed not only for plant response but also for their persistence in the soil, leaching potential, and impacts on native microbial communities [61,71]. In this context, the use of silicate rocks has emerged as a promising strategy, with studies by Conceição et al. (2022) [72] and Oliveira et al. (2025) [73] reporting increased iron content in bean grains following their application to the soil. The integration of low-impact iron sources such as natural chelators, organic matter complexes, nanoenabled systems, or soil amendments (e.g., compost, biochar, rock powder, humic substances) can enhance iron bioavailability while supporting soil health [74,75]. The selection of iron sources should thus reflect a balance between agronomic efficacy, nutritional outcomes, and long-term sustainability.

3.7. The Impact of Iron Biofortification on Public Health

The reviewed studies suggest that the widespread consumption of beans has led this crop to be one of the earliest targets of agronomic biofortification research in the early 21st century [76]. Rice, in turn, is considered the most consumed cereal in various parts of the world, particularly in Asia, and together with beans, forms the dietary foundation of the Brazilian population [33]. Despite their nutritional value in terms of energy and vitamins, the low iron and Zn content in these crops motivated research into their biofortification.

This review indicates that most agronomic biofortification studies are driven by concern over malnutrition and health issues caused by micronutrient deficiencies in the global population. In this context, low-income populations are the most vulnerable, particularly due to limited access to nutrient-dense food [4,8,28,34].

In Nigeria, 75% of children and 67% of pregnant women are anemic [28]. Unequal income distribution, food waste, and poor dietary habits are key factors contributing to the global figure of 870 million malnourished individuals [4]. In light of the recommended daily iron intake levels (

Table 4. Recommended dietary iron intake levels for the population (mg/day).

Age	Men	Women	Pregnant	Lactating
Up to 6 months	0.27	0.27	-	-
7–12 months	11	11	-	-
1–3 years	7	7	-	-
4–8 years	10	10	-	-
9–13 years	8	8	-	-
14–18 years	11	15	27	10
19–50 years	8	18	27	9
50+ years	8	8	-	-

), it becomes evident that meeting these nutritional demands is particularly challenging for low-income populations with limited access to iron-rich foods.

As a response to these nutritional challenges, biofortification has emerged as a promising strategy to enhance the iron content of staple crops and improve dietary intake in vulnerable populations. To meet the recommended daily iron intake, it is important to advance biofortification research focused on plant nutrition, aiming to increase iron content through soil or foliar fertilization [8]. However, such efforts must also incorporate genetic improvement strategies in order to reach the estimated 2 billion individuals affected by iron deficiency globally within the next decade.

In this context, iron biofortification research—especially in rice and beans—is critical, considering their central role in the diets of many countries. These efforts may contribute to increasing micronutrient intake and mitigating health issues linked to nutritional deficiencies worldwide.

The potential of iron biofortification to reduce anemia and related health burdens is significant, especially in regions where rice and beans are dietary staples. However, public health impacts will only be fully realized if biofortified crops are produced sustainably, distributed equitably, and integrated into broader food and health systems. This calls for close collaboration between agricultural scientists, soil experts, nutritionists, and policymakers [61,77].

Beyond improving iron intake, biofortified staple crops can act as vehicles for transforming agricultural practices, shifting production systems toward more climate-resilient, nutrient-efficient, and socially inclusive models. When supported by appropriate incentives and extension services, these systems can empower smallholder farmers, increase local food sovereignty, and reduce reliance on costly supplementation programs [24,74].

3.8. Limitations and Engineering-Based Solutions for Iron Biofortification

Agronomic iron biofortification in rice and beans is a promising strategy to improve the nutritional quality of staple foods consumed by vulnerable populations. In addition to increasing iron concentrations in grains, this approach offers practical advantages for farmers, including low cost, immediate applicability, and compatibility with diverse agricultural systems. However, several challenges and limitations remain that hinder the widespread implementation and scalability of these strategies.

Among the most significant challenges are edaphoclimatic variability, limited translocation of iron to edible tissues, and the frequent presence of antagonistic nutrient interactions, particularly with phosphorus and manganese, which reduce iron solubility and uptake [11,48]. Furthermore, the efficiency of iron fertilization is affected by soil pH, organic matter content, and redox conditions, especially in flooded rice cultivation systems where iron toxicity is also a concern [13].

Many studies fail to address long-term impacts, focusing instead on short-term trials without evaluating the cumulative effects on soil health, nutrient cycling, or environmental safety [12]. The lack of region-specific recommendations, especially in smallholder contexts, often leads to low adoption rates. Social barriers such as limited farmer training, inadequate access to chelated iron sources, and poor integration with extension services further constrain the effectiveness of biofortification strategies [8,9].

Moreover, most studies prioritize agronomic outcomes (e.g., yield, grain iron content) without assessing the bioavailability of iron in human diets, which is a critical determinant of public health impact [23,34]. The use of iron forms such as ferrous sulfate and Fe-EDTA has shown positive agronomic responses, but their real benefit to human nutrition depends on their interaction with anti-nutritional factors and the broader dietary context [22,51].

To overcome these challenges and enhance the applicability of iron biofortification, engineering approaches must be incorporated into the design and implementation of fertilization systems. Agricultural engineering provides a set of tools and technologies that can optimize nutrient use efficiency, reduce environmental risks, and facilitate the large-scale adoption of biofortification strategies in diverse production systems.

Agronomic iron biofortification offers not only nutritional benefits but also opportunities for technological innovation and integration into modern crop production systems. The use of advanced fertilization techniques, such as fertigation, controlled-release formulations, and micronutrient chelates, can significantly enhance the efficiency of iron uptake and translocation to edible tissues. These tools allow precise nutrient delivery, reduce environmental losses, and are compatible with mechanized and large-scale farming systems [24,59].

Modern precision agriculture tools, including georeferenced soil mapping, proximal sensors, and variable rate application (VRA) technologies, allow site-specific diagnosis of iron availability and deficiency zones. These data-driven systems support targeted interventions, minimizing nutrient waste and enhancing the response to iron fertilization. Integration with remote sensing and crop modeling platforms can further optimize timing and dosage based on crop development and climatic conditions [61,75].

Controlled-release fertilizers and nano-enabled iron formulations, such as iron oxide nanoparticles or chelated compounds (e.g., Fe-EDDHA), offer superior solubility and root availability, especially in alkaline or phosphorus-rich soils [11,32]. These technologies reduce fixation losses and prolong iron availability in the rhizosphere, aligning nutrient supply with plant demand.

In irrigated systems, fertigation provides an efficient method for applying soluble iron directly to the root zone, with uniform distribution and minimal waste. The engineering design of fertigation systems, including emitters, injection devices, and flow control, plays a central role in adapting this technology to diverse cropping systems, particularly in tropical agriculture [50]. Additionally, mechanized foliar spraying, aided by electrostatic or low-volume equipment, allows the application of iron directly to photosynthetically active tissues, bypassing soil constraints and improving grain enrichment.

Emerging trends in agricultural automation, including the use of IoT (Internet of Things), sensor networks, and machine learning, enable real-time monitoring and adaptive iron management. These innovations support the development of decision support systems (DSS) that integrate crop models, weather data, and sensor feedback to generate dynamic iron application recommendations [28,60].

Lastly, engineering economic tools such as cost–benefit analysis and life cycle assessment (LCA) can evaluate the viability and sustainability of different iron biofortification methods under local conditions. These assessments support the design of efficient systems that are both technically sound and economically feasible for smallholder and commercial farming contexts [57,58].

In summary, the integration of agricultural engineering into iron biofortification initiatives has the potential to transform this strategy into a precision-based, resource-efficient, and scalable solution. By bridging agronomic knowledge with technological innovation, it is possible to overcome current limitations and achieve broader impacts on food security, soil sustainability, and public health.

4. Conclusions

Agronomic biofortification is a technically feasible and scalable strategy to improve the nutritional quality of staple food crops such as rice and beans, especially in regions affected by iron deficiency. The reviewed studies showed that iron concentrations in grains increased by up to 76% in beans and 60% in rice, depending on the application method, the iron source used, and local conditions. Foliar spraying and soil fertilization with ferrous sulfate and iron chelates were the most commonly used and effective techniques.

The success of biofortification is influenced by various factors such as soil pH, organic matter content, and nutrient interactions, particularly with phosphorus and manganese. However, most studies were short-term and lacked field validation or assessments of iron bioavailability for human consumption. Only two studies directly evaluated iron absorption in humans, with limited results.

From an engineering perspective, technologies such as controlled-release fertilizers, fertigation, and precision agriculture tools can improve iron uptake efficiency while minimizing environmental risks. Integrating these technologies into biofortification programs can enhance both nutritional outcomes and resource-use efficiency.

In addition to contributing to the SDGs, iron biofortification is a practical approach to improve public health and promote the sustainability of food systems. Future research should prioritize long-term field studies, evaluate iron bioavailability in diets, and refine application methods tailored to local agricultural realities.

In conclusion, iron biofortification in rice and beans is not only a nutritional intervention but also an opportunity to embed engineering innovation into food production systems, promoting resilient, sustainable, and health-oriented agriculture.