Slow-release fertilizers: what they are and how they work
Los slow release fertilizers, also known as SRF (Slow Release Fertilizer), are fertilizers designed to sustainably supply essential nutrients to plants over an extended period of time. This type of fertilizer is essential to ensure a continuous and balanced supply of elements such as nitrogen, match, potassium and in many cases Magnesium y micronutrients.
The main benefit of these fertilizers is that They release their nutrients gradually, which helps avoid the nutritional peaks and deficiencies characteristic of conventional fast-release fertilizers. This is achieved through special coatings or a chemical formulation that delays the product's solubility, allowing the nutrient supply to extend from several weeks to several months, regardless of weather conditions.
Main types of slow-release fertilizers
There are different types of slow-release fertilizers, which are classified based on their composition, operating mechanism, and nutrient release rate. The most notable are:
- Coated fertilizers: They have a semipermeable protective layer made of materials such as sulfur, resins, perforated plastics, paraffin, or rubber. Water penetrates the membrane and gradually dissolves the nutrients, releasing them in a controlled manner.
- Low solubility fertilizers: These include formulations such as urea-formaldehyde, isobutylene diurea (IBDU), crotoliden diurea (CDU), and oxamide. These compounds require a large amount of water and high microbial activity for their decomposition, ensuring a very slow release of nutrients.
- Fertilizers with nitrification inhibitors: They incorporate compounds that delay the conversion of ammoniacal forms of nitrogen to nitrates, preventing nutrient loss through leaching and improving fertilizer efficiency, especially in sandy or waterlogged soils.
Main advantages of slow-release fertilizers
- Constant supply of nutrients: They supply nutrients continuously, avoiding deficits and excesses throughout the entire growing cycle.
- Greater efficiency and sustainability: They significantly reduce losses due to leaching, volatilization, and denitrification, reducing the environmental impact and the risk of groundwater contamination.
- Saving time and effort: Application frequency is reduced, resulting in less fertilization work, lower labor costs, and easier management.
- Lower risk of overfertilization: By releasing nutrients gradually, the risk of toxicity to plants is minimized.
- More uniform plant growth: A more balanced and healthy development is achieved, with less stress for the plants.
Disadvantages and limitations of slow-release fertilizers
- High initial cost: Its advanced technology is more expensive than conventional fertilizers.
- Dependence on environmental factors: Soil temperature, humidity, and pH directly affect the rate of release; in areas with extreme climates, nutrient supply may vary.
- Not suitable for immediate needs: If the crop requires a quick supply of nutrients, they are not the best option.
Are they suitable for my crops?
The application of slow release fertilizers It is suitable for a wide variety of situations:
- Ornamental plants and lawns: Its gradual feed ensures uniform growth and a green lawn for longer.
- Fruit trees and vineyards: They maintain the supply of nutrients throughout the production cycle, achieving healthier fruits and good flowering.
- Horticultural crops: They are perfect for slow-growing species such as tomatoes, peppers, and eggplants, as they require constant, but not excessive, nutrition.
- Forest or hardwood production: Such as oaks, chestnuts, holm oaks, cork oaks and conifers, helping to improve rooting and vigor in the early years.
Practical example: slow-release granulated fertilizer
A very common case is the slow-release granulated fertilizer with magnesium, whose characteristics are usually the following:
- Provides nutrients for up to 8 months.
- Promotes rooting and faster growth.
- Typical composition: 11% Nitrogen, 22% Phosphorus Pentoxide, 9% Potassium Oxide y 4% Magnesium Oxide.
How to use and dosage: Mix with the soil in the planting hole, without directly touching the roots or trunk. Some dosage guidelines:
- 30 g per seedling in 8 cm pots at 1,9 liters (1 kg = 33 plants)
- 50 g per plant in a 2 to 9 litre pot (1 kg = 20 plants)
- 100 g per pot of more than 10 liters (1 kg = 10 plants)
How to properly apply slow-release fertilizers
- Analyze the nutritional needs of your plants: Perform soil analysis to detect deficiencies and adjust fertilizer accordingly.
- Choose the right type of fertilizer: You can choose granules, water-soluble formulations for fertigation, or coated fertilizers depending on the type of crop and application method.
- Distribute the fertilizer evenly: Make sure all plants have access to the same amount of nutrients by distributing the product evenly throughout the root zone.
- Follow the manufacturer's instructions: Apply the recommended doses without exceeding them, as excess can cause salt accumulation even if the release is slow.
- Monitor crop development: Observe the growth and condition of the plants to adjust supplemental fertilization if necessary.
Factors influencing nutrient release
- Soil temperature: The higher the temperature, the faster the release.
- Humidity: Fertilizers require a certain amount of moisture to activate the release process.
- pH: Microbial activity and solubility vary in acidic, neutral or alkaline soils.
- Aeration and microbial activity: Well-aerated soils rich in microbial life favor the decomposition of slow-release organic fertilizers.
Los slow release fertilizers They represent a modern and efficient solution for plant nutrition in agriculture, gardening, and forestry. Their use contributes to improving crop productivity and quality, preventing losses and limiting environmental impact. The key to maximizing their benefits lies in proper selection and application, tailored to the specific needs of the soil and plants.