Iron is an essential micronutrient required by plants for proper growth and development. However, the iron availability in soil is often limited due to factors like high pH, excessive carbonates, phosphates etc. This leads to iron deficiency in plants causing chlorosis or yellowing of leaves. Chelated iron helps overcome this limitation by making iron readily available to plants.
Forms of Iron used in Agriculture
There are mainly two forms of iron used in agriculture - chelated iron and non-chelated iron.
Non-chelated Iron
Non-chelated iron like ferrous sulfate is the most common and inexpensive source of iron used in agriculture. However, it has low solubility and availability to plants as it reacts with soil components. Being insoluble, it cannot be readily taken up by plant roots from soil. This makes non-chelated iron less effective especially in calcareous soils where iron is quickly tied up.
Chelated Iron
Chelated iron forms are prepared by chemically binding iron to organic acids or amino acids. This chelation process makes the iron soluble in water and resistant to reactions with soil components. The two common chelating agents used are ethylenediaminetetraacetic acid (EDTA) and citric acid. Iron forms like Fe-EDTA and Fe-citrate are highly stable and soluble in a wide pH range. The chelate ring structure protects the ionic iron and promotes its absorption by plant roots. This makes chelated iron highly bioavailable to plants.
Advantages of using Chelated Iron
Higher Absorption: Due to its solubility and stability in varied soil conditions, chelated iron agricultural micronutrient carriers have higher absorption by plant roots compared to inorganic iron.
Wide soil compatibility: Chelated iron does not react with carbonates, phosphates and other charged particles in soil. It remains available for plant uptake in a wide soil pH range from 5.5 to 8.
Slow release action: Chelated iron complexes release iron gradually in the root zone ensuring continuous nutrition to plants. This reduces the leaching losses of applied iron.
Higher Effectiveness: With its better absorption and utilization, chelated iron works at very low application rates compared to inorganic iron. Even application of few grams per acre is enough to correct iron deficiencies.
Compatibility: Chelated iron forms are usually compatible with other plant nutrients and agricultural chemicals. This allows combining or tank mixing with other fertilizers and spray solutions.
Economical: Though slightly higher in cost than inorganic iron, the effective small doses of chelated iron offset this extra expenditure through improved productivity and quality.
Thus owing to multiple advantages, chelated iron has emerged as a preferred source of iron fertilizer for agricultural crops worldwide. Let us see some common chelated iron products available and their uses in different crops.
Chelated Iron Products for Agriculture
Fe-EDTA
Fe-EDTA (Iron Ethelynediaminetetraacetic Acid) is the most common chelated iron product used globally. Brand names like Sequestrene 138 Fe, Fequest etc are common Fe-EDTA formulations. It has high stability in a wide soil pH range of 5.5 to 8. Fe-EDTA is effective in correcting iron chlorosis in calcareous soils affecting a variety of crops like citrus, pome fruits, stone fruits, vegetables, field crops, ornamentals etc.
Fe-EDDHA
Fe-EDDHA (Iron Ethylenediamine-N, N ́-bis (2-hydroxyphenylacetic acid) is a next generation chelate known for its extreme stability. Due to its high stability constant, Fe-EDDHA remains available to plants for longer duration. It finds major use in iron supplementation of calcareous soils for high value horticultural crops like strawberry, roses where iron efficiency is critical.
Fe-HEDTA
Fe-HEDTA (iron N-2-Hydroxyethyl-ethylenediamine-N,N′-triacetic acid) is another widely used chelate with similar properties to Fe-EDTA but less costly. It helps iron efficiency in field crops, citrus, vegetables grown in neutral to slightly alkaline soils.
Fe-Sodium EDTA
The sodium salt form of Fe-EDTA called Fe-Sodium EDTA expands the pH efficiency range further in highly calcareous soils. It delivers iron effectively even at pH 7.5 to 8.0 and is used for crops like sugar beet, spinach, palm etc grown in extremely alkaline conditions.
Thus in summary, judicious applications of appropriate chelated iron products based on soil properties is key to overcoming iron deficiency related constraints in crop productivity. Their widespread adoption is revolutionizing micronutrient management globally.
Advancing Chelated Iron Technology
Research is continually working towards developing newer iron chelates to further enhance iron efficiency. Some examples include -
Enhanced Ethylene Diamine chelates: Chelates with extended ethylene diamine chain like Fe-EDDHA, Fe-HEDDHA have improved capacity to retain iron under wider pH range in soil.
Amino acid complexes: Chelation with natural amino acids derived from plants, animals or microbial have yielded iron products like Fe-Proteinate that show synergism with soil biota.
Biodegradable chelates: Chelators framed from renewable biopolymers are being tailored for controlled release of iron matching crop demands. Examples are Fe-Lignosulfonate.
Nanochelated iron: Use of nanotechnology is providing highly reactive nanoscale iron particles wrapped in biodegradable polymers or organic acids for boosted iron assimilation.
This progressive research combines with green chemistry approaches to design next generation specialized iron nutrition solutions aligned with precision agriculture needs. Such continuing innovations will ensure optimal plant iron nutrition sustaining robust yields.
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