by Iron is one of the essential micronutrients required by plants in very small quantities to complete their life cycle. Though needed in minute amounts, iron plays a vital role in various metabolic functions of plants. Lack of adequate iron in soil can lead to iron deficiency which impairs photosynthesis and negatively impacts crop yield and quality. Chelated iron formulations have emerged as an effective way to supply soluble and readily absorbable iron to plants.
Forms of iron in soil
Soil contains both organic and inorganic forms of iron. The inorganic forms include oxides and carbonates which are mostly insoluble and less available for plant uptake. Only 0.1% of total iron present in soil is in plant-available forms. Geological weathering releases iron into soil water in ferrous (Fe2+) and ferric (Fe3+) forms. Under aerobic conditions, ferric iron readily gets converted into insoluble ferric hydroxides making it unavailable to plants. Soil properties such as pH, organic matter and redox potential influence the solubility and speciation of iron.
Symptoms of iron deficiency
Yellowing or chlorosis of younger leaves is the most common visual symptom of iron deficiency in plants. The interveinal regions of leaves turn light green or yellow while veins remain green. In severe cases, entire leaves may become completely yellow. Other symptoms include stunted growth, rosetting, smaller and fewer flowers or fruits. Symptoms first appear in newly developing tissues which are actively growing. Susceptible crop plants include vegetables, fruits, ornamentals, coconut, oil palm etc. Iron deficiency impacts crop productivity and quality.
Chelation – A technique to solubilise iron
Chelation is a process where organic metal binding ligands called chelating agents form stable water-soluble complexes with metals like iron. The ring structure of chelates encapsulates the central metal ion, altering its chemical properties. This solubilises normally insoluble forms of iron making it bioavailable. The metal–ligand bond in chelates protects iron from precipitation or redox changes maintaining it in plant-available forms both in soil and plant tissues. Some commonly used iron chelates in agriculture include EDTA, EDDHA, DTPA and HBED.
Mechanism of uptake and utilization of chelated iron
Chelated-Iron Agricultural Micronutrient when applied as foliar sprays or soil drenches, chelated iron complexes are readily taken up by plant roots. Being soluble and stable, iron is transported through xylem to green tissues. In leaves, iron is released from chelates under influence of enzymes, organic acids and redox changes in chloroplasts. It participates in electron transport chain during photosynthesis. Iron also acts as cofactor for enzymes involved in chlorophyll synthesis, catalyzing nitrogen assimilation and respiration. Proper iron nutrition enhances chloroplast development, pigment biosynthesis and photosynthetic efficiency.
Effects of iron chelation in agriculture
Application of iron chelates corrects iron deficiency and overcomes yield losses in various crops. It improves leaf coloration and promotes vigorous vegetative growth with increased plant biomass. Higher chlorophyll content enhances photosynthetic rate leading to better crop canopy. Early flowering and higher number of flowers/fruits per plant has been reported with iron supplementation. Improved iron nutrition also results in crops with higher iron content, imparting nutritional quality. Iron chelates protect crops from biotic and abiotic stresses to some extent while also alleviating symptoms of iron toxicity. They provide year-long green color and are effective in calcareous and alkaline soils where iron is poorly soluble.
Mode of application
Foliar spray is the most common and effective method to remedy visible iron deficiency symptoms. Soil application through drip or sprinkler irrigation is also practiced for preventive maintenance or correction during early crop growth stages. Chelated iron formulations are usually applied at rates ranging from 0.2% to 1% concentration depending on crop and severity of deficiency. Multiple foliar sprays at 10-15 days interval or 2-3 soil applications ensure adequate iron nutrition throughout the crop cycle. Proper water management is necessary after soil applications to solubilise and translocate iron within the root zone. Timely applications maximize crop responses from iron supplementation.
Influence of agronomic factors
Factors like soil properties, temperature, moisture levels affect bioavailability and uptake of chelated iron by crops. High soil pH (>7.5), calcium carbonate content and flooding reduce iron solubility. Microbial activity and release of organic acids help solubilise iron chelates. Iron is less mobile in calcareous soils requiring multiple applications. Warm soil temperatures aid movement and plant assimilation of iron. Adequate moisture favors root absorption and translocation of iron complexes in xylem. Nutrient imbalances especially manganese deficiency antagonize iron uptake. Proper crop management and balanced fertilization optimize effectiveness of iron chelates.
Future prospects
Developing highly stable iron complexes using advanced ligands holds promise to deliver iron more efficiently to plants. Nanotechnologies may assist design of smart delivery systems encapsulating iron chelates for controlled, site-specific release. Genetic modifications in crops aim to enhance root iron uptake mechanisms and internal translocation ability. Understanding plant-microbe interactions could facilitate harnessing plant growth promoting microorganisms to solubilise iron under adverse conditions. Biostimulants may support physiological processes during iron assimilation. With refinements, chelated iron formulations are expected to play a key role in ensuring global food and nutritional security.
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- Source: Coherent Market Insights, Public sources, Desk research
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