Classification of fertilizers: Scientific selection, empowering a new future for green agriculture

Fertilizer is the "food" of agricultural production, directly related to food security, ecological balance and farmers' income. As global agriculture transitions towards precision and sustainability, a scientific understanding of the classification system of fertilizers has become the core of optimizing fertilization strategies. The traditional single perspective classification has failed to meet the demands of modern agriculture. Only by approaching from multiple dimensions can we precisely match the needs of crops, improve resource efficiency and reduce environmental burdens. Based on authoritative agricultural research, this article systematically classifies fertilizers into five key dimensions and provides practical guidelines for practitioners, helping to promote high-quality agricultural development. 
I. Classification by Source: From Natural to Synthetic, Defining Ecological Footprint 
The source dimension reveals the origin of the fertilizer, directly influencing soil health and environmental sustainability. 
Organic fertilizer: Derived from animal and plant residues or excreta, such as livestock manure, straw compost, and green manure (such as lupine). Its advantages lie in improving soil structure and enhancing microbial activity, but the nutrient release is slow and the content is low. It is suitable for ecological farms and can significantly reduce the risk of soil compaction. 
Inorganic fertilizers (chemical fertilizers): Produced through industrial synthesis, such as urea (nitrogen fertilizer) and superphosphate (phosphorus fertilizer). They have high nutrient concentrations and take effect quickly, but excessive use over a long period can lead to soil acidification. They are indispensable in intensive agriculture and need to be combined with organic fertilizers to balance the ecosystem. 
Biological Fertilizer: A New Category, Containing Active Microorganisms (such as rhizobia and nitrogen-fixing bacteria), which enhance fertilizer efficiency through biological nitrogen fixation or phosphorus release. According to FAO data, its rational application can reduce the usage of chemical nitrogen fertilizers by 20%, and it is a key technical support for the "Zero Growth of Chemical Fertilizers" initiative. This dimension emphasizes: Organic and biological fertilizers are the cornerstone of green agriculture, while inorganic fertilizers need to be used precisely under scientific guidance. Each element in the fertilizer undergoes the "inorganic → organic" entire process in plants.

II. Classification by Nutritional Components: Focusing on Crop Needs, Customizing Nutritional Plans 
The nutritional component dimension is centered around the essential elements for plants, determining the "precision" of fertilization. 
Single-nutrient fertilizer: Contains only one main element, such as urea (nitrogen fertilizer) or potassium chloride (potassium fertilizer). Suitable for areas where specific elements in the soil are deficient, but repeated single application over time can easily lead to nutritional imbalance. 
Compound fertilizer: Contains two or more nutrient elements, such as NPK compound fertilizer (with balanced ratios of nitrogen, phosphorus and potassium). The nutrients are released synergistically, increasing utilization rate, and is widely used in field crops. 
Trace element fertilizers: Supplement "invisible nutrients" such as calcium, magnesium, and zinc, such as zinc sulfate foliar fertilizer. For areas with nutrient deficiencies (such as acidic soil in the south lacking magnesium), it can increase yield by 10-15%, but it has been overlooked for a long time. How do the four warriors of macronutrients (N, P, K) + trace elements (Ca, Mg, S, Fe, Mn, Zn, Cu, B, Mo) + organic (amino acids, humic acid, etc.) boost crop yield? 
Scientific insight: Soil testing is the prerequisite - The Chinese Academy of Agricultural Sciences suggests conducting soil testing and formulating fertilization plans before each crop season, to avoid the simplistic "make-up for deficiencies" approach. 
III. Classification by physical state: Suitable for irrigation systems, enhancing application efficiency 
The physical state dimension is related to operational convenience and technical compatibility, and is particularly crucial in water-saving agriculture. 
Solid fertilizers: In the form of granules or powders, such as compound fertilizer granules and lime. They are convenient for storage and transportation, suitable for traditional broadcast application or mechanical deep application, but are prone to loss due to wind erosion and rainwater. 
Liquid fertilizers: Water-soluble solutions or suspensions, such as water-soluble fertilizers and amino acid liquid fertilizers. They can be directly used for drip irrigation or foliar spraying, with an absorption rate as high as 90%, which is in line with the water and fertilizer integration system of smart agriculture. Amino acids, peptides, and fish protein water-soluble fertilizers: Understanding these three brothers can triple the fertilization effect! 
Gaseous fertilizers: For instance, carbon dioxide gas fertilizer, which is used in greenhouses to enhance photosynthesis. Although its application scope is limited, it can increase crop yield by over 15% in facility agriculture. 
Practical value: In arid regions, the combination of liquid fertilizers and drip irrigation technology can save 30% of water and 20% of fertilizer, making it a model of efficient resource utilization.

IV. Classification by Release Characteristics: Regulating the Pace of Fertilizer Effectiveness, Protecting the Ecological Environment 
The release characteristic dimension addresses the issue of "when to release", reducing point-source pollution at its source. 
Quick-release fertilizer: The nutrients dissolve rapidly, such as ammonium nitrate. It is suitable for periods when crops urgently need nutrients (such as during the regreening stage), but it is prone to being washed away by rain, leading to water body eutrophication. 
Slow-release fertilizers: Delayed release is achieved through coating or chemical synthesis, such as urea coated with sulfur. The fertilizer effect lasts for 2-3 months, reducing the frequency of topdressing and increasing the nitrogen utilization rate to over 50%. 
Controlled-release fertilizers: These are smartly responsive to environmental factors (such as temperature and pH), such as polymer-coated fertilizers. They enable "on-demand fertilization", accounting for 30% of the high-end market in Europe and the United States, and are a key focus of green fertilizer research in China. 
Environmental significance: Slow-release/controlled-release fertilizers can reduce ammonia volatilization by 40%, making them an important tool for achieving the "carbon neutrality" goal in agriculture. According to the "China Green Agricultural Development Report", the promotion of such fertilizers can reduce nitrogen oxide emissions by over 1 million tons annually. 
V. Classification by Function: Matching growth stages, optimizing management strategies 
The application dimension focuses on the sequence of field operations, embodying the agricultural wisdom of "adapting measures to the circumstances". 
Base fertilizer: Applied to the bottom layer of the soil before sowing, mainly consisting of organic fertilizer or long-lasting compound fertilizer, to lay the foundation for growth. 
Fertilization: Supplement during the growth period. Use quick-release fertilizers or liquid fertilizers. Precisely control the growth process during critical periods such as tillering and grain filling. 
Leaf fertilizer: Directly spray on the leaves, such as potassium dihydrogen phosphate, used to correct nutrient deficiencies or for emergency remediation. It is absorbed quickly but has a short duration of effect. There are certain points to consider when using leaf fertilizers! 90% of people spray it in the wrong place, which is why the results are poor! (The usage methods and precautions for leaf spraying) 
Management Key Points: The base fertilizer should be substantial and stable; the top-dressing fertilizer should be precise; and the foliar fertilizer should be timely. The synergy of these three approaches can increase the overall fertilizer utilization rate to 45% (an increase of 15 percentage points compared to the traditional method)

Conclusion: Classification equals productivity. Together, we build sustainable agriculture. 
The multi-dimensional classification of fertilizers is not an academic game; rather, it is a bridge connecting science and practice. It helps farmers abandon the old model of "fertilizing by experience" and shift to precise management based on "observing the soil, the plants, and the environment". Under the dual missions of food security and ecological protection, we call for: with classification as the guideline, and technology as the wing, let every grain of fertilizer maximize its value. Choose organic and biological fertilizers to protect soil life; apply slow-release and water-soluble technologies to reduce resource waste; rely on soil testing formulas to achieve increased production and efficiency. Only in this way can we draw a green picture of harmonious coexistence between humans and nature on the fields of harvest. 
Choosing scientific fertilizers means choosing a sustainable future - making agriculture greener and making life better!