**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

#### *Agronomic Biofortification of Food Crops: A Sustainable Way to Boost Nutritional Security DOI: http://dx.doi.org/10.5772/intechopen.103750*

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:


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

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


#### **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 ammoniumbased 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**).

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].

*Agronomic Biofortification of Food Crops: A Sustainable Way to Boost Nutritional Security DOI: http://dx.doi.org/10.5772/intechopen.103750*

**Figure 3.** *Ways of biofortification.*

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:


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

### *Agronomic Biofortification of Food Crops: A Sustainable Way to Boost Nutritional Security DOI: http://dx.doi.org/10.5772/intechopen.103750*

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:


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.*


**Table 1.**

*Nutritional profile of pulse grains.*

*Agronomic Biofortification of Food Crops: A Sustainable Way to Boost Nutritional Security DOI: http://dx.doi.org/10.5772/intechopen.103750*

### **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**).

#### **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

#### **Figure 5.**

*Overview of mechanisms involved in microbe-mediated biofortification.*


#### **Table 2.**

*Type of biofortification done on crops through agronomic approaches.*

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**).
