Agronomic Biofortification of Food Crops: A Sustainable Way to Boost Nutritional Security

Abstract

After the green revolution, there has been a substantial increase in the productivity of food crops. But the nutritional aspect of crops could not keep pace with the growing demand of the population. This has led to a rise in malnutrition problems, especially in developing countries, due to a lack of balanced nutrition. Agronomic biofortification, the process of increasing micronutrient content in food crops through agronomic approaches, is seen as an important process to improve the status of malnutrition in the world. It is seen as a quick, safe, and cost-friendly approach to provide iron, zinc, and other micronutrients in our everyday diet. Unlike molecular/genetic approaches, agronomic biofortification is done on existing crops and varieties and hence the product is easily accepted by the consumers. Approaches like integrated nutrient management (INM) based on soil test values, microbial application, foliar spray of nutrients, can substantially increase the level of micronutrients, vitamins, folic acid, etc. in our food. With sufficient research interventions and awareness programs, agronomic biofortification can serve as a tool to improve the nutritional status of the world.

1. Introduction

Malnutrition, the devil of hidden hunger has already gained its ultimate importance after setting of Millennium Development Goals (MDGs) followed by Sustainable Development Goals (SDGs). The problem of malnutrition is reached in every corner of the Earth. Worldwide, it has been reported that around 2 billion people are affected by malnutrition [1]. Among them, nearly 850 million individuals experience the ill effects of undernourishment on this planet [2]. In low-income countries like Africa where the estimated risk for micronutrient deficiencies is high for Ca (54% of the continental population), Zn (40%), Se (28%), I (19%) and Fe (5%) [3]. Malnutrition mainly affects women and younger children in different forms in developing countries. An abysmal estimate of 151 million children under the age of 5 years are reported to be “stunted” and 51 million falls under the “wasting” category, that is, no proportionate weight as per the height [4]. 79.1% of India’s children between the ages of 3 and 6 years, and 56.2% of married women (15–49 years) are anemic [5]. Vitamin A deficiency affects 169 million preschool children in South and Southeast Asia (33% of all preschool children) and 104 million (32% of all preschool children) in sub-Saharan Africa [6]. Various factors are responsible for malnutrition, but the unavailability of a balanced diet is the prime cause of it. The increasing deficiency of micronutrient in soil reduces the essential elements like minerals, vitamins in food and helps in malnutrition. Micronutrient deficiencies, even mild to moderate ones, can cause serious human health issues, such as impaired metabolic function, decreased immunity, and thus higher susceptibility to infections, growth failure, cognitive impairment, and, eventually, reduced productivity. Micronutrient deficiencies, even mild to moderate ones, can cause serious human health issues, such as impaired metabolic function, decreased immunity, and thus higher susceptibility to infections, growth failure, cognitive impairment, and, eventually, reduced productivity [1]. Hidden hunger can be prevented by direct (nutrition-specific) as well as indirect (nutrition-sensitive) interventions (Figure 1) [7].

Figure 1.

Percentage of the population affected by undernutrition by country, according to United Nations statistics from 2012 (source: Wikipedia).

Direct interventions focus on consumption behavior of humans and include dietary diversification, micronutrient supplementation, modification of food choices and fortification, whereas nutrition-sensitive interventions address the issue of malnutrition and include biofortification.

Fortification is a feasible, cost-effective, and sustainable practice for delivering the content of essential micronutrients, vitamins, and minerals (including trace elements) in the food, that improve the nutritional quality of the food and help to reduce the risk of public health problems. Biofortification, on the other hand, is the process of improving the nutritional quality of food crops using agronomic methods, traditional plant breeding, or modern biotechnology [8]. Biofortification differs from conventional fortification in that it tries to boost nutrient levels in crops during plant growth rather than using manual methods during crop processing. Biofortification may thus be a viable option for reaching populations where supplementation and traditional fortification methods are difficult to implement and/or limited [8]. Biofortification is primarily focused on staple crops which are starchy in nature like rice, wheat, maize, sorghum, millet, sweet potato, and legumes because they dominate diets worldwide, particularly among the groups which are vulnerable to micronutrient deficiencies, and provides a feasible way of reaching malnourished populations with limited access to diverse diets, supplements, and commercially fortified foods [9].

The major drawbacks in biofortification through traditional plant breeding or genetic engineering is not only it require a long gestation period, adequate fund but also the products are not accepted in every country. Whereas agronomic biofortification is the easiest, fastest, and widely accepted way to reach the poorest of the poor rural masses and make foods rich in micronutrients, vitamins, Folic acids, etc. For example, Integrated application of AMF, P, and irrigation regimes on okra have given an increase in average total N, P, K, Ca, B and Mo uptake by 8, 24, 5, 14, 8 and 40%, respectively, over their non-AMF treatments [10].

2. Need for biofortification

Micro-nutrients are vitamins and minerals needed by our bodies in small quantities. However, their impact is critical, and its deficiencies create serious ill-health (WHO) like chronic diseases and stunting, weakening of immune system and reproductive systems and reducing our physical and mental abilities. More than 2 billion people suffer from micronutrient malnutrition and >20 million mortalities annually [11, 12]. It is also referred to as “hidden hunger”. Among which Zn and Fe deficiencies rank 5th and 6th and mostly persisting in low-income countries (Ten leading causes of illness and disease in low-income countries, [13]. Children and women are most susceptible to micronutrient deficiencies. WHO estimates that, in 2017, over 6.3 million children under 15 years old and 5.4 million of them under 5, died as a result of malnutrition), particularly micronutrients [14]. This is mainly due to poor intake of proteins and micro-nutrients like Iodine, iron, Zinc, or monotonous food habit, lack of access to high-quality micro-nutrient-rich foods. Poor intake of micronutrient enriched food by pregnant mother’ results in stunting of children when they were in the womb of the mother. Malnutrition is estimated to affect more than half of the world’s population, making it one of humanity’s most critical global concerns. Conventionally industrial fortification and pharmaceutical supplementation are major steps for alleviating malnutrition issues. But these things are low reachability to poor income countries sometimes they reluctant to intakes of this tablet. So, the efficiencies of these strategies are low. So as an innovative step Biofortification introduced, it is an act of breeding nutrients into food crops, is a relatively low-cost, long-term way of increasing micronutrient delivery. This strategy not only reduces the number of severely malnourished persons who need complementary therapy but will also assist them in maintaining their improved nutritional condition. Moreover, Biofortification is a practical way to address impoverished rural people who may not have access to commercially available fortified foods and supplements. They have cereal-based food habit which has less protein and vitamin and soils of this region are low in Zn (50%), Fe (30%), and iodine, most of the soil is degraded due to alkalinity and salt issues [15]. Micro-nutrient deficiencies affect yield, the various metabolic functions of crops like seed formation, flowering, and quality of foodstuffs. Some micronutrients, especially B, Mg, and Cu are involved in cell wall stability and strength and thus increase plant resistance against pathogen penetration. So agronomic fortification is also a major concern of biofortification. fortification not only insists on intensifying micro-nutrient content but also increase the bioavailability of micronutrient and reduce the quantity of anti-nutritional factors.

Three main difficulties that must be addressed in order for biofortification to be successful:

1. A biofortified crop must be high yielding and profitable for the farmer;

2. A biofortified crop must be efficacious and effective in reducing micronutrient malnutrition in humans; and

3. A biofortified crop must be acceptable to both farmers and consumers in target regions [16].

3. Ways of biofortification

Because traditional therapies are ineffective, biofortification has been advocated as a long-term alternative for increasing mineral nutrition [17]. Biofortification is a method that improves both mineral content and bioavailability in the edible parts of staple crops. The former can be accomplished through agronomic intervention, plant breeding, or genetic engineering, whereas mineral bioavailability can only be influenced through plant breeding and genetic engineering (Figure 2).

Figure 2.

Biofortified crops produced by different approaches-Breeding, Transgenic and Agronomic.

4. Agronomic approaches for bio-fortification

A sufficient and balanced diet that supply the energy pathways and essential amino acids (lysine, methionine), vitamins (A, B, C, D and E), minerals, folic acids, ionic elements (Fe, Zn, I and Se) is possibly the most important contribution to human health and prophylaxis. Micronutrient deficiencies such as iron (Fe), zinc (Zn), iodine (I) and deficiency of vitamin A in soil and plants, which eventually appear as malnutrition in humans are one of the major causes of human disease burden in the developing world. This results in severe impairments of human health and development and affects physical growth, immune system, cognitive development, maternal mortality, etc. A huge increase in food production must be achieved to feed the ever-increasing world population and to sustain human well-being. To meet the challenge of food security, agricultural production must be increased on the existing land, and therefore crop production must be intensified per unit of land.

There are 17 essential plant nutrients that are required by plants for their proper growth and development. Carbon (C), hydrogen (H), and oxygen (O) are not considered mineral nutrients but are the most abundant elements in plants and can be obtained from water and air. The remaining 14 are classified as macronutrients and micronutrients based on the relative requirement of these nutrients by plants. The macronutrients are nitrogen (N), phosphorus (P), potassium (K), sulfur (S), calcium (Ca), and magnesium (Mg). Compared with the macronutrients, the concentrations of the eight micronutrients iron (Fe), zinc (Zn), manganese (Mn), copper (Cu), boron (B), chloride (Cl), molybdenum (Mo), and nickel (Ni) are very small. Four additional elements sodium (Na), cobalt (Co), vanadium (V), and silicon (Si) have been established as beneficial micronutrients in some plants. If a single essential plant nutrient is available in insufficient quantity, it affects plant growth and thus the yield. Micronutrients are often referred to as minor elements, but this label does not mean that they are less important than macronutrients. Micronutrient deficiency or toxicity can reduce plant yield just like macronutrient deficiency or toxicity does, as they serve many important and critical functions in plant metabolism, growth and overall development of the plant.

Agronomic biofortification is the process of increasing the density of nutrients, vitamins and minerals in a crop by means of adopting proper agronomic practices and can be considered as an effective strategy for supplementation of micronutrients powders and enhancing dietary diversity.

The major advantages of agronomic biofortification are:

1. It is practiced on crop cultivars already being cultivated by the farmers and have good consumer acceptability of the produce

2. Enhanced micronutrient concentration in grain and other parts of the crop can be achieved in the same year

3. Very less amount of micronutrient is needed when the foliar application is followed

4. No investment is needed for new seed

5. Agronomic biofortification always creates a win–win approach for developing countries.

The agronomic practices by which we can increase nutrient concentration in edible part:

1. Maintaining soil health physical, chemical, and biological properties

2. Proper cultivation practices

3. Balanced and integrated nutrient management

4. Other practices

4.1 Maintaining soil health physical, chemical, and biological properties

Soil health is one of the important factors regulating plant health by providing optimum conditions like proper root growth, increasing availability of nutrients, moisture-holding capacity and biological activity, optimum aeration, etc. for plants to grow which helps to increase nutrients concentration on edible parts.

4.1.1 Soil physical properties

The availability of micronutrients significantly depends on soil texture. Sandy soil has fewer micronutrients compared to fine-textured soils, because of its high water and nutrient holding capacity. In case of reduced moisture condition rates of dissolution and diffusion of nutrients get reduced and root activity is also reduced. Good soil structures like loose, crumby, and granular possess good porosity, less compaction, high nutrient, and moisture-holding capacity, increase nutrient uptake compared to platy and blocky structured soils, which helps proper root growth hence providing more qualitative yield. Application of organic matter, amendments, press mud, tank silt, bentonite clay can improve soil structure, as well as they increase water and nutrient holding capacity which helps to increase nutrients, folic acid, vitamins in crops.

Though submergence can increase Fe, Mn increases but the uptake of other macro and micronutrients are reduced. So proper drainage facilities are also essential for nutrient uptake and translocation to grains, bulbs, stems, fruits, etc.

4.1.2 Soil chemical properties

Soil chemical properties also possess their impact on maintaining quality and quantity crop products. If the soil has a high buffering capacity, it can provide or resupply more nutrients to the crops. Soil CEC and AEC also possess a great impact on both micro and macronutrient availability. Soils with high CEC hold more nutrients and provide them when the crop needs them. Increased base saturation in soils increases the availability of nutrients like Ca, Mg, K and other cations. Nutrients also become less available to crops in too acidic or too alkaline conditions. In acidic conditions availability of calcium magnesium potassium declined but in alkaline conditions Mn, Zn, Cu may become less available. Availability of Phosphorus is less at too low or too high pH.

Proper soil chemical and physical properties are needed for successful biofortification. Application of gypsum, sulphur compounds on alkaline soil, and lime on acid soils can help to maintain soil chemical properties.

4.1.3 Soil biological properties

Optimum biological activity is needed for faster mineralization of the nutrients. An increasing number of microorganisms like PGPR, AMF, and mycorrhiza act as an extension of the root system and can mobilize or solubilize both mobile and immobile nutrients and make them available to plants. Some macro-organisms like an earthworm, mole cricket, ants make the soil more porous and help the roots to penetrate deeply. So biological activity plays a crucial role in biofortification in a sustainable way. Application of organic matter, the addition of legume crops in the cropping system, less use of pesticides can increase biological activity in the soil.

4.2 Proper cultivation practices

4.2.1 Tillage

Tillage is an important practice for most crops. Proper tillage can provide the most suitable soil conditions where crops can germinate, grow up and complete the life cycle. Tillage eliminates weeds, disease inoculants and provides a competitive advantage to the crops. Tillage at optimum moisture conditions (i.e., 50–75% MHC) is crucial for tillage operation as more or less moisture can create hardpan in subsoil which restricts root growth and hence reduce nutrient uptake and yield. Now a days reduced tillage, or zero tillage is gaining its importance, but soil compaction is the main problem for them as it creates problems in root proliferation [18]. Stipesevic et al. [19] reported that in winter wheat Zn concentration in the plant tissue at the beginning of heading did not differ due to tillage treatments in the first 2 years, but in the third year it was 11.7 mg kg⁻¹ in the conventional tillage plots and only 6.4 mg kg⁻¹ in the zero-till plots. Subsoil or Chisel plow once in 3–4 years is a solution for them. Some improved tillage practices like a ridge and furrow planting, Furrow irrigated raised bed planting (FIRB) also help to increase the nutrient uptake by the crops.

4.2.2 Water management

As most of the nutrient uptake is done by mass flow and diffusion so soil moisture is the main factor that affects nutrient concentration in crop products. Optimum moisture helps in better root growth, increases the solubility of nutrients, and makes it available to the plants. Both excess and deficit water reduce nutrient concentration from the root zone by leaching or restricting mobilization. Sometimes mild stress can increase nutrient concentration in grains. Water deficit during grain filling can decrease lipid content in wheat grains but mild water deficit would be beneficial to the grain filling and starch compositions, significantly improving bread-making quality [20]. Proper management of water in the wheat field at the post-harvest stage was helpful both to improve protein content and composition of wheat grain, but water deficit/water stress at the pre-anthesis stage can increase P, Ca, Mg, K, and Zn. Proper management of water in all the critical stages is important for improving the quality of the product. Continuous flooding throughout the rice-growing season reduces Cu and Zn plant availability while increasing B, Fe, and Mn availability in both limed and un-limed acid laterite and alluvial soils. In comparison to continuous flooding under above-ground soil conditions, alternate flooding and drying were shown to be favorable to rice because it considerably enhances the availability of B, Cu, and Zn nutrients to plants while decreasing the availability of Fe and Mn nutrients.

4.3 Balanced and integrated nutrient management

Nutrient application is the most important step for the agronomic ways of biofortification. Integrated use of compost, manure, organic and inorganic fertilizer, microorganisms is the best way for a sustainable way of biofortification. Here we will discuss these things.

4.3.1 Application of organic matter

Soil organic matter influences greatly soil physical, chemical, and biological properties. It improves soil structure, soil porosity, bulk density, helps in stabilizing soil aggregates and other soil physical properties. For alkaline and saline soils, it also acts as a reclaiming agent. Besides improving soil health, it also has the capacity to supply all other nutrients to plants. Fe which is largely present in the insoluble form as Fe³⁺, organic matter can increase its solubility through the effect of redox potential [21]. Fulvic acids, humic acids which are formed during the decomposition of organic matter help to increase Fe solubility and its availability to plants. Whereas other nutrients like Cu, Ni are tightly bonded with the organic fraction of soil which makes them less available. The addition of green manure, compost, biosolids, and biocharcauses more uptake of soil-bound Zn and other nutrients and intensifies the plant availability of zinc [22]. These amendments also decrease heavy metal uptakes like Cd in rice [23]. The addition of organic matter shows a considerable increase in microbial biomass carbon, microbial community diversity. These biological properties of soils may help to maintain nutrient cycling and soil quality. The foods grown in organic conditions have greater nutrient content including minerals and vitamins [24]. So, we can blindly say that if we want successful biofortified crop products by the agronomic way, organic matter is the only solution.

4.3.2 Application of synthetic fertilizers

Application of macronutrients like N, P, and K is recommended based on soil test values and nitrogen should be applied in split doses. These nutrients promote root and shoot growth and increase uptake of all nutrients by the plants. Intensive use of macronutrient fertilizers sometimes supplies micronutrients as micronutrients are added with these during manufacturing process or present as impurities. High doses of nutrients like N, P, and K reduce the uptake of nutrients which has low phloem mobility like Ca, as Ca is prone to dilution effects [25]. Over-reliance on ammonium-based fertilizers limits cation nutrient uptake and decreases the carbohydrate content of root vegetables by increasing root respiration [26]. Excess soil P causes more phytate content and can promote Zn deficiencies. Whereas excess consumption of K intervenes Ca and Mg uptake [26]. So, judicious use of macronutrients is most important to help in the proper uptake of other nutrients.

4.3.3 Micronutrient application and bioavailability

Micronutrients simply follow a straight pathway to reach into the human body from the soil through the crop and food. The success of agronomic biofortification in alleviating micronutrient deficits in humans is determined by several important parameters. The parameters are mostly influenced by nutritional bioavailability at various stages (Figure 3).

Figure 3.

Ways of biofortification.

Soil application of micro-nutrients can increase grain nutrient content like soil application of Zn increase Zn concentration in cereal crops for 2–3 times depending on crop species [27] and crop genotype [28]. In basmati rice grain and straw, green manure and Zn-coated fertilizers enhanced nutritional content and absorption. Foliar fertilization of 0.2 % zinc sulfate recorded a higher Zn concentration in rice, whereas Zn-coated urea (ZCU) as ZnSO₄.H₂O registered the highest total Zn uptake [29]. Kaur [30] found a considerable increase in micronutrient uptake (Zn, Fe, Mn, Cu, and B) in wheat after applying 100 percent P, 10 kg Zn, and 1 kg B ha⁻¹. Kumar et al. [31] reported that increasing the application of boron levels from 0.5 to 1.5 kg ha⁻¹ should reduce B use efficiency and the highest value (9.2%) was obtained at a lower level of applied B (0.5 kg ha⁻¹), whereas the lowest was found (4.2%) with B applied at 1.5 kg ha⁻¹. The foliar spray helps to transport the nutrients from the site of application to the site of utilization in a rapid way. Fe, Zn, and Mn are applied in chelated form and translocation within the plants was found greater [32]. Foliar fertilization with ZnSO₄ and Zn EDTA and other chelates has been used in fruits and vegetable production. From these vegetative parts, nutrients will translocate to the edible parts.

In rice, Zn and Fe are localized in protein bodies in the outer layer of the grains, which is often removed during processing (de-husking, milling) leaving less Zn and Fe in the consumed rice [33, 34]. Rice parboiling is an effective method to increase nutrient contents especially when micronutrients are added to the soak water during the parboiling, as the process drives nutrients from the bran and germ layer to the endosperm [35, 36].

Application of 120 kg Si ha⁻¹ increased rice yield to the tune of 17.1%, 7.1% and 2.0%, respectively, over 0, 40 and 80 kg Si ha⁻¹ [37]. So, we can say that only application of micronutrients is not sufficient for successful biofortification, its bioavailability also needs to take into consideration.

4.3.4 Through the application of Microorganisms

The most active site for the soil microorganisms in the rhizosphere where the nutrients are sequestrated, mobilized, and made available to plants. Bio-fortification of the crops can be done by using bio-fertilizer or microbial inoculants which mobilize or solubilize the essential nutrients and possess a positive impact on plants’ health.

Most organisms possess both direct and indirect effects for improving plant health and nutrient concentration on grain and biomass. The microorganisms like PGPR, AMF fungi, Cyanobacteria, Actinomycetes are the major drivers.

4.3.4.1 Role of PGPR

PGPR helps to increase the nutrient concentration in the rhizosphere in different ways:

1. They release growth-promoting compounds and mineral solubilizing enzymes which play an important role in the cycling of nutrients

2. They modify root morphology and thereby increase the root surface area which helps in more nutrient uptake

3. Sometimes they secret Phyto-siderophores which increases micronutrient availability in soil

Inoculation of bacterial strains like Pseudomonas putida, Pseudomonas fluorescens, Azospirillum lipoferum increase iron concentration up to two to three times in rice [38]. Rana et al. [39] observed that the treatment involves Providencia sp. bacteria can increase zinc copper Ion concentration in wheat grain. Santiago et al. [40] found that Fe concentration in the biomass of wheat could increase up to 1.5-fold when the plot is treated with a siderophore-producing strain Trichoderma asperellum. Tariq et al. [41] reported that commercial application of Pseudomonas sp. in rice soil improve Zn concentration up to 157% in rice. Pseudomonas sp. and Actinobacteria sp. inoculation improve uptake of Fe, Mg, Ca, K and P by crop plants [42].

4.3.4.2 Role of Fungi

Most of the fungi are being heterotroph (saprotrophs, biotrophs and necrotrophs) in nature so they play an important role in regulating soil fertility by decomposing and cycling of organic matter and minerals.

Arbuscular mycorrhiza has an extensive hyphal network that spread both internally and externally in the roots. They explore the soil more efficiently as their hyphae have some specific characteristics like faster growth rate, thin and extensive branches. AM fungi can increase forage area up to 100 times as compared the root length of the crop. AMS has the ability to improve the supply of N, P, Cu, Zn, Fe, Ca, B, Mn, Ni, K, etc. [43].

Some Ecto-mycorrhizal fungi also produce low molecular weight organic acids that help more nutrient mobilization.

Due to the application of AMF+ P+ Proper irrigation in okra total N, P, K, Ca, B and Mo uptake was increased 8, 24, 5, 14, 8 and 40%, respectively whereas in the case of pea, an increasing amount of total N (8%), P (19%), K (12%), Mg (12%), Ca (22%), Zn (22%), Fe (10%), Cu (28%), Mn (10%), B (11%) and Mo (38%) uptake was also addressed in AMF imbedded treatments over non-AMF counterparts [10].

4.3.4.3 Role of Cyanobacteria

Cyanobacteria or blue green algae is the plant growth-promoting agent which is also a major player in nutrient uptake and improving user efficiency. They increase nutrient concentration in plants by:

1. The counter deleterious pathogenic activity and maintain good plant health.

2. They produce allelochemicals like IAA, extracellular polysaccharides which stabilize the soil and increase N and C in the rhizosphere regions.

3. They help in sequestering nutrients and improving their mobilization into plants.

When Anabaena-based biofilm inoculants were used in rice soils under flooded and SRI methods of rice cultivation that increases 13–46% iron and 15–41% zinc in rice grains respectively. In Anabaena-Pseudomonas-based biofilm treatments, rice grains showed an increase in copper accumulation.

Cyanobacterial inoculation helps to increase rice crop yields (grain yields) to the extent of 10–24% in diverse locations in the world, especially in South Asia [44].

4.3.4.4 Role of Actinomycetes

Actinomycetes can play a significant role to dissolve the primary rock-forming minerals to obtain essential nutrients and act as nucleation sites for the precipitation of secondary minerals. In this way, it helps to uptake nutrients by plants (Figure 4).

Figure 4.

Agronomic biofortification is the application of micronutrient-containing mineral fertilizer (blue circles) to the soil and/or plant leaves (foliar), to increase micronutrient contents of the edible part of food crops.

5. Other practices

5.1 Crop rotation

The beneficial effects of crop rotation include improved soil chemical and physical fertility, reduced weed infestation and diseases. Karlen et al. [45] concluded that crop rotation and cover crops may increase the availability of Fe, Cu and Zn.

In rice-wheat rotation use of FYM and green manurer maintained the available fraction of soil micronutrients like Fe, Zn, Cu and Mn compared to the same rotation fertilized with inorganic fertilizer alone [46].

The addition of pulse crops in the cropping system is the best option after cereals for improving eating quality, not only because of their importance for humans and animals but also due to their soil ameliorative values and their ability to thrive under harsh and fragile environments (Table 1).

Pulses	Energy (kcal/100 g)	Vitamin (mg/100 g)				Nutrient (mg/100 g dry weight)
		Thiamine (mg)	Riboflavin (mg)	Niacin (mg)	Vitamin C (mg)	Fe	Zn	Ca	Mg	K
Chickpea (Cicer arietinum L.)	368	0.5	0.2	1.5	4	6.2	3.4	105	115	875
Pigeon pea (Cajanus cajan L.)	342	0.6	0.18	2.9	—	5.2	2.7	130	183	1392
Lentil (Lens culinaris)	346	0.8	0.2	2.6	4.4	7.5	4.7	56	122	955
Mung bean (Vigna radiata L.)	345	0.6	0.2	2.2	4.8	6.7	2.7	110	189	1246
Urdbean (Vigna mungo L.)	347	0.6	0.2	2.3	4.8	8.4	3.5	55	—	—
Field pea (Pisum sativum L.)	345	0.7	0.2	2.9	—	4.4	3.0	186	115	981
Rajmash (Phaseolus vulgaris L.)	345	0.53	0.22	2.08	1.8	3.4	1.9	80.3	188	1316
Cowpea (Vigna unguiculata)	346	0.94	0.22	2.36	4.6	7.54	3.77	287	250	1450
Horse gram (Macrotyloma uniflorum)	321	0.4	0.2	1.5	—	7.0	—	202	—	—
Moth bean (Vigna aconitifolia)	330	0.4	0.09	1.5	—	9.6	—	—	—	—

Table 1.

Nutritional profile of pulse grains.

5.2 Intercropping

Intercropping between soil exhaustive crop and the regenerative crop can create a complementary relationship and helps to reduce weed and disease infestation, protect the soil from nutrient mining, maintain soil physical, biological health and helps to increase nutrient density on them.

5.3 Proper pest management

Pests like insects, weeds, disease inoculants possess a great impact on the quality as well as quantity of the product. They restrict the growth of the crops, sometimes can kill the plants. They also create a bitter taste in plants by producing some toxins. So proper management of them is of utmost importance. Integrated pest management is the best option to control their infestation as well as to maintain the quality of the product.

5.4 Proper drying and storage

During post-harvest season grains that are not properly dried can sometimes develop mold and also some toxic substances like aflatoxins, ochratoxins, so proper drying is necessary. The grains like rice and wheat are exposed to contaminants, pests and diseases and prone to nutrient losses. So proper storage is important after harvest (Figure 5 and Table 2).

Figure 5.

Overview of mechanisms involved in microbe-mediated biofortification.

Crops		Type of biofortification done through agronomic approaches
Cereals	Rice	Fe, Zn, Se
	Wheat	Fe, Zn, Se,
	Maize	Fe, Se, Zn
	Barley	Zn, Fe
	Sorghum	Protein
Pulses	Soybean	Se
	Chickpea	Zn, Se, Fe, Zn, Ca, Cu, Mn, Mg
	Pea	Zn
	Common bean	Zn; N, P, K, Cu, Mn, Zn
Oilseeds	Canola	Protein, oleic acid, linoleic acid
	Mustard	Se
Vegetables	Potato	Zn, Se
	Sweet Potato	Beta-carotene
	Carrot	Iodine, Se
	Lettuce	Iodine, Se
Fruits	Tomato	Iodine

Table 2.

Type of biofortification done on crops through agronomic approaches.

6. Progress on biofortification

As of 2018, worldwide 6.7 million farm households are producing biofortified crops and these products surely go into food dishes. Till now more than 300 varieties have been released in 30 countries for crops, such as rice, wheat, maize, cassava, orange sweet potato, potato, lentil, beans, cowpea, banana, and plantain [47]. Several institutions like 1. Food Policy Research Institute (IFPRI), Bill and Melinda Gates Foundation (BMG Foundation), Biotechnology Industry Research Assistance Council (BIRAC), Indian Agricultural Research Institute (IARI) must work together to populate biofortified crops and create an enabling environment. Recognition of biofortification among global regulatory agencies, a collaboration between agencies from various sectors, a more active role for private players, and designing new development policies and agendas that take into account the programs currently being implemented on the ground, among other things, are all components of such an environment. CGIAR will continue to employ its varied network of international organizations, research institutes, and civil society organizations around the world to drive a single, integrated conversation on standards and governance, and to provide society with the highest possible return on investment. Harvest Plus is one of them, and it is leading the biofortification project, which it will enable in the next years, with local governments acting as main partners [47].

7. Constraints in agronomic biofortification

Enhancement of crop qualities through agronomic biofortification has the following challenges:

• Timely availability to farmers—Lack of availability of micronutrient fertilizers at the proper time to the farmers leads to farmers mostly skipping their application to the crops, which further leads to widespread deficiencies.

• Low nutrient use efficiency for micronutrients—Micronutrients like iron, zinc, copper, etc. have very low use efficiencies (1–5%) which limit the uptake of applied micronutrients by plants.

• Genetic constraints—Agronomic biofortification has a minor role in enhancing protein content as both are negatively correlated and protein content is genetically controlled.

• Difficulty in public awareness—Iron and zinc deficiencies are widespread in India and around the world. Since their deficiencies stay hidden and are not easily manifested as external symptoms, the creation of public awareness about the adverse effects of iron and zinc malnutrition is important.

• Lack of knowledge—In most crops, a thorough understanding of the mechanisms of mineral translocation from soil to plant is inadequate. As a result, further information regarding the rate-limiting processes of micronutrient acquisition and translocation in the soil-plant system is required.

• Safety in the use of biofortified crops—The safety concerns of biofortified crops have to be analyzed in detail before making them available in the market. A comprehensive knowledge gap also exists in the bioavailability of micronutrients in food grain and mineral distribution patterns in plant systems.

• Post-harvest processing losses—The loss of micronutrients after harvesting, on processes like selective removal of outer tissues during cleaning and processing is not analyzed for most of the crops and needs to be considered.

8. Future prospects

The public sector institutions must give intensive efforts and make policy for promotional campaigns that can significantly increase the acceptance of agronomic practices for biofortification. Providing the micronutrient fertilizers and other bio-inoculants like PGPR, AMF, cyanobacteria can cause the rapid spreading of these agronomic practices. Assured premium remunerative prices for the biofortified products in the market encourage farmers to grow more biofortified foods. Active investment of extension activities would create awareness among farmers’ industries and consumers regarding the availability and benefits of these biofortified crops (Figure 6).

Figure 6.

Percentage of biofortified crops by agronomic means [48].

Some essential steps should be required for the popularization of biofortified crops. These are:

8.1 Awareness generation

Incomplete knowledge of the health benefits of biofortified crops is the major reason for slow adoption. Some demonstration trials should be conducted in the farmer’s field and make sure that farmers would actively participate in this program. Lack of yield compared to conventional practices is also another reason for slow adoption but if farmers get premium prices, they do not lose their interest in this. Strong linkages should be constructed with Agro-processing industries that provide confidence to farmers. Strong promotional extension activities such as field demonstration, conveying a message through TV talk, radio shows and live drama would make the farmers, industry, and consumers aware of the existence and benefits of biofortified crops.

8.2 Policy support

Strengthening input supply is a major step towards the popularization of Biofortified crops. Providing subsidized micronutrient fertilizer, bio-inoculants, or microorganisms, receiving to provide remunerative prices for biofortified grains in the market will encourage farmers. Recently, unveiled National Nutrition Strategy—2017 by NITI Aayog, the Government of India envisages the alleviation of malnutrition in the country through food-based solutions [49].

Inclusion of this biofortified cereal indifferent government-sponsored programs such as National Food Security Mission, Rashtriya Krishi Vikas Yojna as well as nutrition intervention program such as Integrated Child Development Services scheme, ‘Mid-day meal’ and Nutrition Education and Training through Community Food and Nutrition Extension Units would help in providing the much-needed balanced food to poor people. Recently, the Government of India announced the millets like (sorghum, pearl millet, foxtail millet, finger millet, Kodo millet, proso millet, little millet, and barnyard millet), besides two pseudo millets (buck-wheat and amaranthus) as ‘Nutri Cereals’ which have high nutritive values. This would increase their demand in both the regional and Challenges to reach billion people by 2030 worldwide markets, allowing farmers to command better prices. Incorporating biofortified items into these government-sponsored programs would assist youngsters, pregnant women, and the elderly, as well as speed up their distribution. Given the well-documented health benefits of QPM, Ethiopia’s government has set a goal of cultivating QPM varieties on 20% of the country’s total maize land in the future years [50]. As a result, significant government policy support would improve the uptake and acceptance of biofortified crops (Figures 7 and 8).

Figure 7.

Conceptual diagram on future prospects of agronomic biofortification.

Figure 8.

Ways to reach biofortified products to people [50].

8.3 Research interventions

Most nutritional characteristics like (protein, lysine, tryptophan, iron, zinc, and Vitamin c) are invisible. So, it is difficult to convince farmers and Consumers regarding the quality of the product. Large-scale trials should be needed by a public institution that could help in generating more data and thus help in the dissemination of fortified crops research should be needed on nano-fertilizers that have the potential for effective management of nutrients till now biofortification is restricted to some crops show there is a need to bring more crops under these practices.

9. Conclusions

Agronomic approaches provide a short-term solution compared to breeding approaches. The introduction of high-yielding varieties and extreme use of commercial single fertilizers are the main reason behind micronutrient malnutrition problems. With the adoption of proper management practices significant improvement in nutrient concentration has been observed by different scientists. Fertilization with both micro and macronutrients has been reported to increase the nutritional status of the edible portion of a crop. An increase in the concentrations of Zn and Fe with the addition of Zn or Fe fertilizers has been reported in wheat (Triticum aestivum) [26]. Foliar application of Fe and Zn fertilizers has been found to be an easy and effective way of yield and nutrition enhancement in fruits and vegetable crops besides cereals [51]. Water management in winter wheat at the post-anthesis stage was helpful for improving grain quality and nutrient content relevant to the processing and human consumption [20] and the addition of organic matter in the form of green manure, compost, biosolids and biochar caused more uptake of soil-bound Zn and other nutrients and intensify the plant availability of zinc [21] has also been reported. An increase of Fe concentration up to 1.5-fold in the wheat biomass has been found by Watson et al. [22]. Santiago et al. [40] when the plot is treated with a siderophore producing strain Trichoderma asperellum. To feed the ever-increasing population from the limited land resources require proper knowledge of soil-plant interactions and precise information on the status of different agro-ecological regions so that people can get quality food in their dish. In the short term, agronomic approaches are the most important sustainable technique of biofortification. Biofortification has expensive time-consuming regulatory approval processes, and its acceptance is very low in the society. Besides these challenges, biofortified crops hold a very bright future as these have the potential to remove micronutrient malnutrition among billions of poor people, especially in developing countries.

Conflict of interest

The authors declare no conflict of interest.