Fertilizers: What they are, types, uses, and a complete guide for plants and crops

Proper management of plants and crops involves a thorough understanding of all the factors that influence their development, from correct irrigation and pruning techniques to the choice, application and control of nutrients. fertilizersAlthough the concept of fertilizer is often associated solely with agriculture, the reality is that in both gardening and industrial crops, and even in home food production, understanding what a fertilizer is and the different types that exist is essential to ensuring healthy, sustainable, and efficient production.

In this article, we'll cover in detail what a fertilizer is, what it's used for, how it works for plants and soil, and how to choose the most appropriate product for each need and stage of growth. We'll integrate all the key concepts developed in both the technical literature and the best-positioned resources on the Internet, including the different types of fertilizers according to their origin, composition, format, form of application and function, so you can understand and make informed decisions about the best fertilization strategy for your orchard, garden, or farm.

What is a fertilizer? Technical and conceptual definition

A fertilizer is, in general terms, Any substance that supplies essential nutrients in a form assimilable to plants, with the primary objective of promoting growth, improving health, optimizing yield, and maintaining or increasing soil fertility. Fertilizers can be of natural, synthetic, chemical, biological, organic, or mineral origin, and their essential function is to provide the elements the plant requires to optimally complete its life cycle.

According to the definition established by European regulations, a fertilizer is material whose main function is to provide nutrients to plantsThis function can extend to improving soil structure, promoting beneficial biological processes, stimulating root development, or even facilitating the absorption of water and other nutrients.

It is important to differentiate between fertilizer y allowanceAlthough in practice the two terms are often used interchangeably, fertilizer more specifically refers to materials that, in addition to providing nutrients, improve the physical, chemical, or biological properties of the soil. Fertilizer, on the other hand, emphasizes the direct nutritional contribution to the plant. This nuance is important for choosing the product that best suits the needs and objectives of the crop.

Plants require a total of 17 fundamental chemical elements (including macronutrients and micronutrients) to complete their life cycle. The three main ones that are always present in any fertilizer are: Nitrogen (N), Phosphorus (P) and Potassium (K), which are usually indicated in product formulas as their famous NPK ratio. Along with these, there are secondary nutrients (sulfur, calcium, magnesium) and trace elements (iron, copper, zinc, boron, manganese, molybdenum, chlorine, and nickel, among others).

The objective of using fertilizers is twofold:

• Correct nutritional deficiencies of the soil to avoid poor production and achieve healthier, more vigorous and productive crops.
• Maintain and improve soil fertility and structure, avoiding progressive depletion due to continuous cultivation and extraction of nutrients by plants.

Since ancient times, humans have sought ways to replenish the nutrients extracted from each harvest, using everything from Organic fertilizers of animal and plant origin (manure, compost, ashes, crushed bones, guano) to modern developments based on chemical and industrial processes, such as urea or superphosphates.

What is a fertilizer used for and how does it work?

The application of fertilizers pursues several fundamental purposes in agriculture and gardening:

• Provide key nutrients for the balanced development of the plant in all its phases: germination, vegetative growth, flowering, fruiting, ripening.
• Prevent or correct deficiencies which can cause lack of vigor, lower production, early leaf fall, small fruits, poor flowering, etc.
• increase performance and the quality of the harvest (larger size, better color, better flavor, resistance to diseases and pests).
• Restore the productive capacity of the soil after successive cultivation cycles, avoiding degradation and depletion due to overexploitation.
• Optimize water absorption and nutrients, improving the physical and chemical structure of the substrate.
• Promote sustainable agriculture when choosing organic, ecological and biofertilizers, which respect the environment and the microbial biodiversity of the soil.

The mode of action of fertilizers depends on their composition y formulation:

• Soluble and inorganic fertilizers: They quickly release nutrients, which immediately pass into the soil solution and are absorbed by the roots through water.
• Organic fertilizers: They require the action of soil microorganisms to mineralize organic matter and gradually release nutrients, prolonging fertilization over time and improving soil structure.
• Foliar fertilizers: They allow the absorption of nutrients directly by the leaves, acting as a rapid reinforcement in situations of acute deficiency or soils with limited absorption.

Selecting the right fertilizer type, quantity, and application method is crucial, as unbalanced or excessive fertilization can cause plant damage (phytotoxicity), soil imbalances, environmental impacts, and even long-term yield reduction due to salt buildup or contamination.

Essential nutrients: Macronutrients, secondary nutrients and micronutrients

To successfully complete their life cycle, plants require a series of nutrients that can be classified according to the quantity needed and the function they perform in the plant organism.

• Primary macronutrientsThese are the elements that the plant requires in greatest quantity and must almost always be supplied externally for optimal growth. They are:
• Nitrogen (N): essential for vegetative growth, protein formation, leaf and stem development.
• Phosphorus (P): key to root development, flowering, fruit and seed formation, disease resistance.
• Potassium (K): essential in water regulation, fruit quality, resistance to stress and diseases, and sugar transport.
• Secondary macronutrients: Required in smaller quantities than the above, but equally vital:
• Calcium (Ca): formation of cell walls, growth of roots and shoots.
• Magnesium (Mg): central component of chlorophyll, essential in photosynthesis.
• Sulfur (S): synthesis of amino acids and proteins, essential in metabolic processes.
• Micronutrients or trace elements: Elements that the plant requires in minimal quantities, but whose deficiency can cause serious disorders:
• Iron (Fe): chlorophyll synthesis, energy metabolism.
• Zinc (Zn), Copper (Cu), Manganese (Mn), Molybdenum (Mo), Boron (B), Chlorine (Cl), Nickel (Ni), among others.

A good fertilizer should provide the correct combination of these elements, in the appropriate proportion according to the soil condition, the type of plant, and its stage of development. It is common to find fertilizers on the market. NPK fertilizers with different formulations and products enriched with micronutrients to respond to specific needs.

Types of fertilizers according to their origin, composition and function

Fertilizer classification can be based on different criteria, which in turn determine the advantages and disadvantages of each type and the optimal application strategy.

1. According to your the origin

• Organic fertilizers: They are derived from biological materials, such as animal manure, plant compost, guano, crop residues, green manures, and other natural products. They often provide, in addition to nutrients, organic matter that improves soil structure and life.
• Inorganic or mineral fertilizers: Substances of natural origin (mining, salt deposits) or industrially produced (chemical processes) that contain the required elements in mineral and highly soluble form, such as ammonium nitrate, superphosphate, potassium chloride, urea, among others.
• biofertilizers: Products containing live microorganisms (bacteria, fungi, algae) capable of fixing nitrogen, solubilizing phosphorus or mobilizing other nutrients, enhancing soil fertility in a natural and sustainable way.

2. According to your chemical composition

• Simple or uninutrients: They provide a single nutrient (example: urea provides nitrogen, superphosphate provides phosphorus, potassium chloride provides potassium).
• Compounds or multinutrients: They present two or more essential nutrients combined in the same formula (example: NPK, NP, NK, PK, with or without other secondary elements or microelements).
• Organic-minerals: Products that combine organic matter with nutrient minerals, offering a synergistic effect on the soil and the plant.
• mineral amendments: Correctors of specific deficiencies or imbalances, such as calcium, magnesium or sulfur deficiencies.
• Micronutrients: Fertilizers designed to supply specific deficiencies of iron, zinc, boron, copper, etc., in the form of simple or complex correctors (chelates).

3. According to your presentation and format

• Solid: granules, powder, pellets, mixtures.
• Liquids: soluble solutions, concentrated suspensions, extracts (typical in fertigation, foliar or direct applications).
• soft drinks: such as anhydrous ammonia, less common in conventional agriculture but used in large crops.

4. According to your form and time of application

• Bottom fertilizers: They are applied before sowing or planting to prepare the ground.
• Starter fertilizers: administered during sowing or early rooting to stimulate crop start.
• Top dressing fertilizers: applied when the crop is already established, to reinforce vegetative or reproductive development.
• Foliar fertilizers: supplied directly onto the leaves in liquid form, for rapid absorption at critical times or to correct specific deficiencies.
• Fertigation: application through irrigation water, widely used in intensive and hydroponic agriculture.

5. According to your release and absorption rate

• Quick or immediate release: nutrients available almost instantly, although there is a greater risk of leaching or volatilization.
• Slow or controlled release: They incorporate coating or encapsulation technologies that release nutrients gradually, reducing application frequency and leaching losses.

Main types of fertilizers and practical examples

1. Nitrogen fertilizers

• Ammonium nitrate, calcium nitrate, urea, ammonium sulfate: They supply nitrogen in different chemical forms (nitric, ammoniacal, ureic), accelerating the growth of leaves and stems.
• Especially recommended for green leafy crops, grasslands, cereals, turf and horticultural crops in high vegetative growth stages.
• Its application must be careful to avoid burns, leaching and water contamination.

2. Phosphate fertilizers

• Superphosphate, triple superphosphate, monoammonium phosphate (MAP), diammonium phosphate (DAP): optimal sources of phosphorus for root and reproductive development.
• Ideal for cold, compacted soils or soils poor in available phosphorus, and for deep planting.
• La availability depends on soil pHIn acidic soils, it is recommended to adjust the pH before applying large doses.

3. Potassium fertilizers

• Potassium chloride, potassium sulfate, potassium nitrate: They strengthen disease resistance, regulate water absorption, and improve the quality of fruits and vegetables.
• Essential for crops of tubers, fleshy fruits, vines, tomatoes, potatoes, bananas, among others.
• Potassium also contributes to tolerance to drought and heat stress.

4. Compound fertilizers (NPK and variants)

• They combine nitrogen, phosphorus, and potassium in proportions customized for each stage and type of crop.
• There are universal formulas (example: 15-15-15, 10-20-10, 12-24-12), and specific formulas for lawns, flowers, vegetables, fruit trees or extensive crops.
• Many include calcium, magnesium, sulfur and micronutrients to meet complete needs.

5. Enriched and special fertilizers

• Micronutrients: chelates of iron, zinc, manganese, copper, boron, molybdenum: They correct specific deficiencies that appear as chlorosis, necrosis or leaf deformations.
• Humic extracts and amino acids: They improve nutrient absorption, stimulate root activity and help combat abiotic stress.
• Seaweed: natural source of phytohormones and micronutrients, used as biostimulants.

6. Slow and controlled release fertilizers

• Formulated with special coatings (resins, polymers, sulfur) that dissolve under conditions of humidity, heat or microbial activity, allowing prolonged nutrition with lower environmental risk.
• Recommended for lawns, fruit trees, potted ornamentals and highly technical crops.

7. Liquid and foliar fertilizers

• Easy to apply through irrigation, sprinkler, or spraying systems, they allow for quick and targeted corrections.
• Very useful in situations of stress, compacted soils or when there are root blockages.
• They require correct dosage to avoid phytotoxicity.

8. Biofertilizers and biostimulants

• Products inoculated with nitrogen-fixing bacteria (Rhizobium, Azotobacter, azospirillum), mycorrhizal fungi (Glomus), microalgae and other microorganisms that improve nutrient availability and soil health.
• They promote more ecological and sustainable agriculture, increasing the biodiversity and resilience of systems.
• Many are approved for use in ecological agriculture.

Application and practical recommendations: how to choose and use the right fertilizer

The correct selection and application of fertilizers is essential to achieve the desired results without harming the crop or the ecosystem. Several key factors must be considered:

• Preliminary soil analysis: Perform a physical-chemical analysis to determine the pH, amount of organic matter, concentration of available macronutrients and micronutrients, salinity level, and soil texture. This allows for precise product selection and dosage.
• Know the specific needs of the crop: Each species, variety and stage of development requires a specific combination and concentration of nutrients, adjusting the fertilization plan to the phenological cycle.
• Fertilizer type and formulation: Select the most suitable compound (NPK, simple, enriched, biofertilizer, etc.), the ideal proportion and the format (granulated, liquid, foliar).
• Application Method: The delivery method can be applied to the soil (root, bottom, top dressing), by fertigation, or by foliar spray. Each method has specific instructions and advantages.
• Time and moment of application: It must be coordinated with the needs of the crop (pre-sowing, post-sowing, before flowering or setting, etc.), avoiding periods of intense rain that cause washing.
• Dosage and frequencyAvoid excess to avoid phytotoxicity, salinization, or environmental contamination. A fractionated application adjusted to the plant's actual absorption is preferable.
• Compatibility and mixingSome fertilizers and amendments may be incompatible with each other or with pesticides. It's important to consult technical data sheets and perform prior testing.
• Environmental impact and sustainability: opt whenever possible for organic, ecological and biofertilizers, reduce the use of synthetic chemicals, and reuse plant and animal waste from the farm to close the nutrient cycle. A sustainable fertilization plan protects soil and water, maintains biodiversity, and promotes food security and human health.

For extensive crops, the agricultural technology current (sensors, satellite images, weather stations) allows determining variable application zones and optimizing fertilizer distribution to increase yields with the least possible impact.

Advantages and disadvantages of different types of fertilizers

Organic fertilizers

• Advantages: They improve soil structure and life, gradually release nutrients, promote water retention, and promote organic farming.
• Disadvantages: Less soluble and slow to assimilate nutrients, varied and less precise composition, difficulty for applications on large surfaces.

Inorganic / mineral fertilizers

• Advantages: High concentration of nutrients, fast and predictable results, applied accurately and evenly.
• Disadvantages: Increased risk of leaching and contamination, degradation of soil life, salt accumulation, environmental impact, require judicious and technical use.

Biofertilizers and biostimulants

• Advantages: Sustainability, increased nutrient use efficiency, improved soil biodiversity, and long-term cost reduction.
• Disadvantages: Slower or variable effect, depends on management and environmental conditions, may require combinations with other fertilizers for optimal results.

Formats and commercial presentations of fertilizers

• Granules and microgranules: for broadcast application on the ground or in line during sowing.
• Soluble powder: It is dissolved in water and applied by fertigation or conventional irrigation.
• Concentrated liquids: ideal for fertigation, spraying or localized applications.
• Concentrated suspensions: stable mixtures of insoluble active ingredients, easy for the farmer to handle.
• Fertilizer tablets and cuttings: used in pots, ornamental gardening and indoor crops.

Criteria for selecting the ideal fertilizer for each case

• Soil type: its physical and chemical composition, retention capacity, pH and organic matter content.
• Crop type and variety: your specific nutritional needs and sensitivity to imbalances.
• Weather conditions and season: temperature, humidity, rainfall, incidence of frost, etc.
• Agricultural practices and rotations: type of tillage, irrigation systems, previous crops, use of green manures.
• Results of foliar and soil analysis: to adjust fertilization to real deficiencies.
• Cost and availability: seeking a balance between efficiency, sustainability and profitability.
• Environmental and social impact: priority for the health of people, wildlife and the environment.

The rational and planned use of fertilizers, combined with the recycling of organic waste and the integration of agroecological management techniques, constitutes the basis for modern, respectful, and economically viable agricultural production.