Ferrous Sulfate Monohydrate: The “Iron Supplement Expert” in Agricultural Cultivation

In agricultural production, the healthy growth of crops depends on the “nourishment” of various micronutrients, among which iron plays an indispensable role.When crops face an “iron deficiency crisis,” ferrous sulfate monohydrate often steps in as the key solution.

As a commonly used iron supplement fertilizer in agriculture, it safeguards crop growth and improves yields with its high efficiency and excellent bioavailability.This article focuses on the agricultural applications of ferrous sulfate monohydrate, explaining how it has become an essential “iron supplement expert” in the field.

I. Core Fundamentals: Comprehensive Analysis of the Physicochemical Properties of Ferrous Sulfate Monohydrate

To apply ferrous sulfate monohydrate scientifically and efficiently in agriculture, it is essential to understand its basic physicochemical characteristics and identification information.The following table systematically summarizes its key properties to provide theoretical support for practical application:

Property Category	Specific Information	Remarks
English Name	Ferrous sulfate monohydrate	Reference name when purchasing imported products
CAS No.	17375-41-6	Unique chemical identifier for traceability and compliance
Chemical Formula	FeSO₄·H₂O	The active component is divalent iron (Fe²⁺), which is readily absorbed by plants
Molecular Weight	169.92 g/mol	Basic data reference for calculating application dosage
Appearance	Gray-white or light yellow-green crystalline powder	Easily distinguished from ferrous sulfate heptahydrate (blue-green crystals)
Decomposition Temperature	Approx. 64 °C (starts to decompose)	Stable at room temperature; avoid heat sources
Water Solubility	Soluble in water; solubility increases with temperature	Suitable for foliar spraying and root drenching
Theoretical Iron Content	Approx. 31–33%	Higher than most organic iron fertilizers—one of its core advantages
pH (1% solution)	3.0–4.0 (weakly acidic)	Helps improve alkaline soils and enhances iron availability
Stability	Stable at room temperature, hygroscopic, easily oxidized to ferric iron in air	Should be sealed during storage; mixing with organic fertilizer can slow oxidation
Hazard Level	Low toxicity; slight irritation to skin and mucous membranes	Wear gloves during handling; avoid direct contact

II. Agricultural Perspective: The Core Advantages of Ferrous Sulfate Monohydrate

Based on its physicochemical properties, ferrous sulfate monohydrate shows multiple advantages in agricultural use, making it a preferred iron supplement fertilizer.

Its excellent solubility is a major highlight. Once dissolved, Fe²⁺ ions are evenly distributed in solution, allowing efficient absorption by crops.With a theoretical iron content of about 31–33% and a high proportion of ferrous iron, its bioavailability far exceeds that of many organic iron fertilizers—one of the key reasons it is widely used in agricultural iron supplementation.

Compared with the commonly used ferrous sulfate heptahydrate, the monohydrate form has a higher density, higher iron content, and easier transport due to lower crystal water content. It is less prone to caking caused by water loss from crystals but remains somewhat hygroscopic, so sealed storage is still necessary.

III. Core Agricultural Value: Dual Role in Iron Supplementation and Soil Improvement

In agriculture, ferrous sulfate monohydrate provides dual benefits—precise iron supplementation for crops and auxiliary soil improvement. These functions complement each other, creating an optimal environment for plant growth.

• Iron Supplementation: The Key Driver of Chlorophyll Formation

  
  

  Iron is not a structural element of the chlorophyll molecule itself but an essential activator of chlorophyll-synthesizing enzymes, making it indispensable for photosynthesis. Without iron, chlorophyll cannot form properly.

  
  

  When crops suffer from iron deficiency, the most typical symptom is iron chlorosis: young leaves turn yellow first (while older leaves remain green as iron is immobile), interveinal chlorosis develops, and in severe cases, leaves wither and drop, photosynthesis is hindered, and plant growth slows—leading to reduced flowering, lower yields, or even crop failure.

  
  

  Ferrous sulfate monohydrate provides bioavailable Fe²⁺ that can be directly absorbed by roots or leaves, quickly participating in chlorophyll synthesis and reversing chlorosis to restore plant vitality.

• Soil Improvement: The Assistant for Local pH Adjustment

  
  

  Beyond direct iron supplementation, ferrous sulfate monohydrate also helps improve soil conditions. In alkaline soils, available iron tends to oxidize and precipitate as ferric compounds that are unavailable to plants, even when total soil iron content is high.

  
  

  The weakly acidic nature of ferrous sulfate monohydrate helps locally lower soil pH, break the fixation of iron in alkaline environments, and increase iron availability. It can also reduce soil compaction and improve aeration, promoting healthier root development.

• Indirect Benefits: Hidden Support for Stress Resistance and Crop Quality

  
  

  Iron is also crucial for the activity of various enzymes, including those related to nutrient metabolism and protein synthesis. Applying ferrous sulfate monohydrate enhances the activity of antioxidant enzymes such as peroxidase and catalase, thereby improving crop resistance to stress.

  
  

  Enhanced photosynthesis allows plants to accumulate more sugars, vitamins, and other nutrients, significantly improving the sweetness, color, and nutritional quality of fruits and vegetables.

IV. Practical Agricultural Guide: Scientific Application Methods for Different Scenarios

The effectiveness of ferrous sulfate monohydrate largely depends on the correctness of application methods. According to crop growth stage, soil condition, and degree of iron deficiency, the following three approaches are commonly used:

1. Base Fertilization: Long-Term Iron Supply and Soil Improvement

Base fertilization is applied before sowing or transplanting to address soil iron deficiency at its source and provide continuous iron nutrition throughout the crop growth cycle.This approach is particularly effective in long-term iron-deficient or alkaline soils, delivering dual benefits of iron supplementation and soil improvement.

Mix ferrous sulfate monohydrate thoroughly with organic fertilizer before incorporation into the soil. Organic matter provides balanced nutrients, enhances water and nutrient retention, prevents direct contact between ferrous sulfate and seeds or roots (avoiding burn), and slows oxidation of Fe²⁺ to Fe³⁺.Dosage should be adjusted according to iron deficiency severity—slightly less for sandy soils and slightly more for clay soils.

2. Foliar Spraying: Rapid Rescue from Iron Deficiency

When crops already show chlorosis, foliar spraying offers the quickest and most effective remedy. Fe²⁺ ions are directly absorbed through leaves, participating immediately in chlorophyll synthesis. New leaves usually regain greenness progressively, preventing further damage.

• Concentration Control is Crucial:

  
  

  • Fruit trees (apple, pear, citrus): 0.2–0.3% solution

    
    

  • Vegetables (tomato, cucumber, spinach): 0.1–0.2%

    
    

  • Flowers (rose, azalea, gardenia): 0.05–0.1% to avoid leaf burn.

    
    

• Spraying Tips:

  
  

  Fully dissolve ferrous sulfate before use. Apply on cloudy days or in the evening when light and evaporation are weak to extend absorption time.

  
  

  Focus spraying on the undersides of young leaves, where stomata density is higher. For severe symptoms, repeat spraying every 7–10 days for 2–3 applications.

  
  

3. Root Drenching: Targeted Supplementation for Specific Crops

Root drenching is suitable for crops with developed root systems and mild deficiency symptoms, such as strawberries, peppers, and potted flowers.Prepare a 0.1–0.2% solution and slowly pour around the root zone, ensuring penetration to the active root layer. Avoid heavy irrigation beforehand to prevent dilution, and lightly loosen the soil afterward to improve absorption.

4. Suitable Crops: Those Most in Need of Iron Supplementation

Iron sensitivity varies among crops.

• Fruit trees: Apple, pear, citrus, peach, and grape are prone to iron deficiency, especially in alkaline soils. Regular application prevents chlorosis and improves fruit yield and sweetness.

  
  

• Vegetables: Tomato, cucumber, spinach, celery, and cabbage benefit from improved leaf color and vigor after application.

  
  

• Flowers: Azalea, gardenia, rose, orchid, and jasmine prefer acidic soils and are highly responsive to iron supplementation, resulting in brighter flowers and greener foliage.

  
  

• Field crops: Wheat and rice may show reduced tillering or spikelet numbers under iron deficiency, which can be mitigated by timely application.

  
  

V. Key Principles: Safe Application and Proper Storage

To maximize the benefits of ferrous sulfate monohydrate and avoid adverse effects, proper use and storage are essential.

1. Application Precautions

• Avoid Mixing with Alkaline Substances:

  
  

  Ferrous sulfate monohydrate is acidic and reacts with alkaline fertilizers or pesticides (such as lime, wood ash, or ammonium bicarbonate), causing Fe²⁺ oxidation to Fe³⁺, leading to reduced efficacy or precipitation that can burn crops.

  
  

  Avoid mixing with phosphate fertilizers as well, as insoluble iron phosphate may form. If both are needed, apply them at least 7–10 days apart.

  
  

• Avoid Overapplication:

  
  

  Excessive use may lead to soil acidification, disrupt microbial balance, or cause iron toxicity—manifested as brown leaf spots and root decay. Always follow recommended dosages and conduct small-area trials first.

  
  

• Avoid Spraying Under Strong Sunlight or High Temperature:

  
  

  Rapid water evaporation under strong light concentrates the solution and can scorch leaves. High temperature also accelerates Fe²⁺ oxidation, lowering absorption efficiency.

  
  

2. Storage Guidelines

Store in a cool, dry, and ventilated area away from direct sunlight and rain. Moisture causes caking and oxidation.Keep packaging tightly sealed; once opened, use promptly and reseal any remaining product.For long-term storage, adding a small amount of reducing agent or sealing under nitrogen can effectively prevent oxidation.

VI. Conclusion: The Core Advantages and Scientific Value of Ferrous Sulfate Monohydrate in Agriculture

With its high bioavailability, stability, and flexible application methods, ferrous sulfate monohydrate stands out as a powerful solution to crop iron deficiency.

It not only replenishes iron efficiently and corrects chlorosis but also improves soil structure and nutrient conditions, promoting healthy and high-quality yields.

By mastering proper application techniques and safety precautions, farmers can fully leverage this “iron supplement expert” to safeguard crop growth.

Whether in orchards, vegetable fields, or flower gardens, the rational use of ferrous sulfate monohydrate ensures stronger, healthier, and more productive plants.