Iron – a Vital Micronutrient for Agricultural Crops

Iron (Fe) is an essential micronutrient for plants, playing a crucial role in various physiological and biochemical processes.

While iron deficiency is a common issue, understanding its broader functions and management in agricultural crops can significantly enhance crop yield and quality.

Iron deficiency symptoms in leaves of apple, Poland. Photo courtesy of ICL.

What is the importance of iron in plants?

1. Photosynthesis and chlorophyll synthesis: Iron is fundamental for the synthesis of chlorophyll, the pigment responsible for photosynthesis. Without adequate iron, plants cannot produce sufficient chlorophyll, leading to reduced photosynthetic activity and stunted growth.
2. Enzyme function: Iron is a key component of many enzymes involved in energy transfer, nitrogen reduction and fixation, and lignin formation. These enzymes are vital for plant growth and development.
3. Proteins: iron is found in cofactors ensuring the activity and the stability of metalloproteins involved in vital physiological processes (e.g., respiration, photosynthesis, sulfur and nitrogen assimilation, amino acid biosynthesis). The chloroplasts are particularly rich in iron–sulphur proteins such as Photosystem I, ferredoxins and a range of metabolic enzymes.
4. Respiration: Iron plays a critical role in cellular respiration, a process that converts sugars into energy. This energy is essential for various plant functions, including growth and reproduction.

Why is iron deficiency common despite its abundance on Earth?

Iron deficiency is widely spread even if Fe is the fourth most abundant element on Earth. This is because iron is mostly present in soils in the form of poorly soluble oxides/hydroxides, especially at neutral to alkaline pH.

Iron deficiency symptoms in leaves of kiwi, Italy. Photo courtesy of ICL.

Which are the symptoms of iron deficiency in plants?

Iron deficiency symptoms typically first appear on the youngest leaves of the plant. This is because iron is not very mobile within the plant, so when there is a deficiency, the new growth is affected first.

Iron deficiency in plants is characterized by several distinct symptoms:

1. Interveinal chlorosis: The most common symptom is interveinal chlorosis, where the leaf veins remain green while the areas between them turn yellow. This condition primarily affects young leaves and can lead to reduced growth and yield if not addressed promptly.
2. Stunted growth: Plants suffering from iron deficiency often exhibit stunted growth due to impaired photosynthesis and reduced energy production.
3. Poor fruit and flower development: Iron deficiency can lead to poor development of fruits and flowers, affecting both the quantity and quality of the yield.
4. Leaf necrosis: In severe cases, iron deficiency can cause necrosis (death) of leaf tissue, starting at the leaf margins and progressing inward.

Iron deficiency symptoms in leaves of strawberry, France. Photo courtesy of ICL.

Which are the symptoms of iron toxicity in plants?

While iron is essential, excessive iron can be toxic to plants. Iron excess can lead to plant growth defects and reduced crop yields due to the generation of harmful reactive oxygen species (ROS) in the presence of hydrogen peroxide.

Symptoms of iron toxicity include bronzing and stippling of leaves, particularly in rice grown in waterlogged conditions. Managing soil pH and proper irrigation practices can help prevent iron toxicity.

Which factors affect iron availability?

1. Soil pH: Iron availability is highly dependent on soil pH. In alkaline soils (high pH), iron becomes less soluble and less available to plants. Acidic soils (low pH) generally have more available iron.
2. Soil composition: Soils rich in organic matter tend to have higher iron availability. Conversely, sandy soils with low organic content often have lower iron levels.
3. Waterlogging: Excessive water can lead to anaerobic conditions, reducing iron availability. Proper drainage is essential to maintain optimal iron levels in the soil.

What is the significance of iron in crop production?

1. Cereal crops: Iron is vital for the growth of cereal crops like wheat, rice, and maize. Adequate iron levels ensure healthy root development and efficient nutrient uptake, leading to higher yields.
2. Legumes: Leguminous crops, such as soybeans, clover, chickpea and lentils, require iron for nitrogen fixation. Iron is a component of nitrogenase, the enzyme responsible for converting atmospheric nitrogen into a form usable by plants.
3. Vegetables and fruits: Iron is crucial to produce high-quality vegetables and fruits. It enhances the nutritional value and marketability of crops like tomatoes, spinach, and citrus fruits.

Iron deficiency symptoms in leaves of corn, USA. Photo courtesy of Prof. John Sawyer, ISU Extension agronomist (Iowa State University)

How can iron availability be enhanced in agricultural crops?

1. Iron chelates: Applying iron chelates can effectively supply iron to plants. Chelates are compounds that bind iron, keeping it in a soluble form that plants can easily absorb.
2. Foliar sprays: Foliar application of iron solutions can quickly correct iron deficiencies. This method is particularly useful for crops showing immediate deficiency symptoms.
3. Soil amendments: Adding organic matter, such as compost or manure, can improve soil structure and increase iron availability. Organic matter helps retain moisture and nutrients, making them more available to plants.

Iron deficiency symptoms in leaves of winegrape, Brazil. Photo courtesy of ICL.

Which ICL fertilizers supply iron?

Fertilizers containing iron are essential for preventing iron deficiency in crops, ensuring optimal plant growth and enhancing overall agricultural productivity. Some of the ICL fertilizers that supply iron include:

Foliar Fertilizers:

• Agroleaf® Liquid Iron: A premium liquid foliar feed designed to prevent iron deficiency. Suitable for all crop types, especially soft fruits, it contains 4.4% chelated iron and features ICL’s advanced F3 SurfActive technology for improved spreading, adhesiveness, and retention.
• Agroleaf® Foliar Line: Fully water-soluble NPK formulations with chelated micronutrients, including iron.

Water Soluble Fertilizers for Fertigation:

Most of ICL’s water soluble fertilizers contain iron and micronutrients for full nutrition of crops through fertigation systems. Some examples are:

• Agrolution® Liquid: This line contains iron chelated with EDTA and other micronutrients, ideal for fertigation of all crop types to prevent or correct nutrient deficiencies.
• Solinure®: A water-soluble NPK fertilizer line with micronutrients, including iron, designed for fertigation of field or greenhouse fruit and vegetable crops.
• Agrolution® Special: NPK water-soluble fertilizers enriched with a fully-chelated micronutrients package, including iron. The acidifying effects of these formulations make more nutrients available to crops.
• Nova® Complex Optima: NPK fertilizers enriched with sulfur and a fully-chelated micronutrients package, including iron. These water-soluble fertilizers contain DMPP, which reduces nitrogen leaching and improves overall nitrogen efficiency.

Granular Fertilizers for soil application:

• ICL PKpluS®: A line of PK (phosphorus and potassium) granulated fertilizers based on Polysulphate, containing five nutrients in a single granule: phosphorus, potassium, sulfur, magnesium, and calcium. Tailor-made formulae with additional micronutrients, including iron, are available upon request.

Iron Management in crop production

Iron is a critical micronutrient for agricultural crops, influencing various physiological processes and overall plant growth. By understanding the factors affecting iron availability and implementing effective management practices, farmers can optimize crop production and ensure sustainable agricultural practices.

Preventing iron deficiency requires proactive soil management and precise nutrient application. Regular soil and plant testing helps assess iron availability and informs fertilization practices to maintain optimal levels. Consult an ICL agronomist for advice on how to correct and prevent iron deficiency.