Fertilizers can be categorized in various ways. The primary classification is based on their composition, dividing them into three main categories: organic fertilizers, inorganic fertilizers (chemical fertilizers), and biological fertilizers. They can also be further subdivided based on factors such as the speed of nutrient release, physical form, and chemical properties.
Classification by Core Composition
Organic Fertilizers: Derived from plant or animal residues and waste-such as farmyard manure, compost, oil-cake fertilizers, or well-rotted chicken manure-these are rich in organic matter. They improve soil structure and provide long-lasting, though slow-releasing, nutrients.
Inorganic Fertilizers (Chemical Fertilizers): Produced through chemical synthesis or mineral extraction, these contain high concentrations of nutrients and act quickly. Subcategories include nitrogen, phosphorus, and potassium fertilizers, as well as compound fertilizers and those containing micronutrients.
Biological Fertilizers: These contain specific active microorganisms (e.g., microbial inoculants or bio-organic fertilizers). They help mobilize soil nutrients and improve the nutritional environment for crops; for optimal results, they should be applied in conjunction with organic or chemical fertilizers.
Classification by Nutrient Release Rate
Fast-Acting Fertilizers: Nutrients are readily available for rapid absorption by plants-examples include urea and potassium dihydrogen phosphate-making them ideal for quick nutrient supplementation during specific crop growth stages.
Slow-Release/Delayed-Action Fertilizers: Nutrients are released gradually over an extended period-such as coated slow-release fertilizers or well-rotted compost-which helps minimize nutrient loss and reduces the frequency of application.
Classification by Chemical Properties
Acidic Fertilizers: These include physiologically acidic fertilizers (e.g., ammonium sulfate), chemically acidic fertilizers (e.g., potassium dihydrogen phosphate), and organically acidic fertilizers (e.g., well-rotted compost). They are suitable for amending alkaline soils.
Alkaline Fertilizers: Examples include calcium-magnesium-phosphate fertilizer and plant-ash; these can be used to adjust the pH of acidic soils.
Neutral Fertilizers: Such as urea, which has minimal impact on soil pH and is suitable for a wide range of applications.
