Biuret, also known as dibiuret, is a significant topic in the field of agriculture and fertilizers. As an unavoidable by-product of urea production, biuret is present in small quantities but can have potential effects on crop growth and the environment.
This article provides a detailed analysis of biuret, including its origin, characteristics, benefits and drawbacks, potential hazards, detection methods, prevention strategies, and mitigation measures to enhance understanding of this compound.
I. What is Biuret? Its Characteristics and Formation
Definition:
Biuret is a by-product formed when urea undergoes a dehydration-condensation reaction under high-temperature conditions. Found as an impurity in urea-based fertilizers, its formation is closely linked to production processes.
1. Chemical Formula:
NH2−CO−NH−CO−NH2
2. Characteristics:
Appearance: A white or pale-yellow crystalline powder with strong hygroscopic properties.
Solubility: Soluble in water and ethanol.
Chemical Stability: Decomposes slowly in aqueous solutions, ultimately releasing ammonia and carbon dioxide.
3. Formation Mechanism: Biuret is commonly produced in urea-based fertilizers (e.g., compound fertilizers) during granulation at high temperatures (above 130°C). Prolonged high temperatures increase biuret content:
Major Processes: Rotary drum granulation, tower granulation, and ammonization granulation.
Impact of Poor Control: If production temperature exceeds 170°C or time is poorly managed, biuret content increases significantly, heightening the risk of fertilizer-related phytotoxicity.
II. Biuret Detection and Standards
Detection Methods:
Spectrophotometry:
Uses the chromogenic reaction between biuret and copper salts to detect concentrations at specific wavelengths. This method is simple and suitable for industrial applications.
High-Performance Liquid Chromatography (HPLC):
A more precise method capable of simultaneously measuring urea and biuret content, suitable for research and high-precision requirements.
International Standards:
Strict limits exist for biuret content in urea fertilizers across different countries:
China:
Premium-grade urea: Biuret content ≤ 0.9%.
Standard-grade urea: Biuret content ≤ 1.5%.
European Union: Urea biuret content ≤ 0.5%.
United States: Urea biuret content ≤ 1%.
III. Effects of Biuret on Crops
1. Potential Benefits:
Slow-Release Nitrogen Source:
Biuret decomposes slowly, providing a stable nitrogen supply over time, making it suitable for certain long-term crops.
Enhanced Protein Synthesis:
Under controlled application, biuret indirectly participates in plant metabolism, promoting photosynthesis and protein synthesis.
Environmental Stability:
In specific soil conditions, biuret is more stable than urea, reducing nitrogen volatilization losses.
2. Negative Impacts:
When biuret content is excessive in urea fertilizers, significant adverse effects can occur:
Root Damage:
Biuret inhibits the growth of fine roots, essential for nutrient and water absorption, leading to "root burn" or distorted root structures.
Impaired Photosynthesis:
In foliar fertilization, biuret causes leaf scorch, yellowing, and defoliation, reducing photosynthetic efficiency and affecting yields.
Seedling Toxicity: China:
Fertilizers with biuret content >1% are unsuitable as seed or seedling fertilizers. Content >2% significantly lowers germination rates and seedling growth.
Crop Toxicity Symptoms:
Leaf tip yellowing and curling.
Blackened or shortened roots.
Stunted growth and wilting.
Abnormal fruit development.
IV. How to Mitigate Biuret’s Impact on Crops
Preventive Measures:
Choose High-Quality Urea:
Farmers should opt for low-biuret urea, especially for sensitive crops such as fruit trees, vegetables, and rice.
Controlled Application Methods:
Avoid direct contact between urea and seeds or seedlings. Incorporate fertilizers into the soil promptly to reduce root damage.
Scientific Fertilization Practices:
Use a "small but frequent" fertilization strategy to ensure efficient nutrient uptake while minimizing biuret toxicity.
Remedial Actions:
Dilution through Irrigation:
Increase irrigation frequency to dilute biuret concentration in the root zone, reducing its harmful effects.
Apply Organic Fertilizers:
Organic fertilizers enhance microbial activity in the soil, accelerating biuret decomposition.
Foliar Fertilization:
Spray 0.2%–0.3% potassium dihydrogen phosphate, brassinolide, or amino acid-based fertilizers to improve crop resilience and recovery.
Crop Replacement:
For heavily contaminated soils, consider soil improvement or planting biuret-tolerant crops.
V. Conclusion
Biuret is a common by-product in urea fertilizer production, with its formation closely tied to manufacturing processes. While biuret offers some agricultural benefits under controlled conditions, its potential to harm crops highlights the importance of managing its content. Through careful fertilizer selection, scientific application, and effective mitigation strategies, farmers can minimize the adverse effects of biuret, ensuring safe and efficient agricultural practices.
Promoting awareness and technological advancements in producing low-biuret fertilizers are essential for reducing environmental risks and supporting sustainable farming practices.
