What is a Slow-Release Fertilizer?

Explore the benefits and workings of slow-release fertilizers (SRF), perfect for providing consistent nutrients over time, improving soil health, and reducing leaching.

Table of Contents

Both young and mature plants need nutrient supply over an extended period, which is why slow-release fertilizers (SRF) are commonly used. 

A slow or controlled-release fertilizer is a kind of fertilizer that aids in a slow but consistent supply of nutrients during stages such as flowering or fruiting. It’s a less-soluble compound with high MW(Molecular Weight), which releases its nutrients by the breakdown of its biodegradable coatings(usually polymer or resin). By providing a consistent nutrient content to the plants, it aids in steady growth and overall plant health. 

Understanding the workings and functions of SRF fertilizers can be beneficial for agricultural enthusiasts to make informed decisions and get a good yield. Therefore, in this article, we will look into it. 

Categories of SRF (Slow-Release Fertilizers)

Categories of SRF Slow-Release Fertilizers

Slow-release fertilizers can broadly classified into 3 categories; let’s discuss them: 

Polymer coated

These types of SRFs usually have a semi-permeable layer of polymer coating that allows water to dissolve the nutrients. Generally, these work on the diffusion principle. Because of the biodegradable coating, they may improve soil structure over time.  

Resin coated 

Resin-coated SRF also works on the diffusion principle. However, resin coating offers longevity due to less water infiltration. Therefore, it aids in reduced leaching and sustained nutrient supply over time. 


These kinds of slow-release fertilizers do not have any physical barriers or coatings. However, they are less soluble and aid in a controlled nutrient supply, too. 

How do slow-release fertilizers work?

Let’s start by understanding it working on a molecular level. The magic of slow-release fertilizer is in its composition and coating technology. The nutrients in an SRF are packed in a form that plants cannot take up instantly. Plus, the grains in slow-release fertilizers are coated with a semi-permeable resin layer that regulates the slow release of nutrients into the soil. In simple terms, this coating is similar to a barrier that allows nutrients to pass in controlled amounts. Once water molecules break down the polymer or resin, big pores are created, allowing the release of more complex amounts. 

This mechanism of controlled release goes for longer times in slow-release fertilizers. The end goal is to supply the nutrients at different stages; these kinds of fertilizers help improve the overall health of the plants. 

Benefits of slow-release fertilizer 

There are several benefits of using slow-release fertilizers; let us take a look at some of them:

Controlled nutrient supply

The extended-release fertilizers provide the plants with essential nutrients at the right times and even save them for future usage. Plus, the chances of leaf burn to sudden nutrient spikes are greatly decreased, aiding in better growth of plants. 

Improved soil health 

slow-release fertilizers Improved soil health

The slow-release fertilizers foster an atmosphere for bacteria like fungi and protozoa to thrive, which break down the organic matter and aid in nutrient release. As a result, soil structure and its water retention capabilities are increased. In addition, a variety of microbes in soil ensure that the soil is free from any diseases. 

Reduced nutrient leaching 

As the nutrients are released slowly over a period, fewer nutrients are leached during heavy rainfall. Therefore, it is also good for the environment. Plus, due to a regular and steady supply of nutrients, the plants are always equipped to survive through conditions such as droughts.  

Parting comments 

Slow-release fertilizers can be an ideal choice at some stages when nutrients are required for an extended period. It can lead to several benefits ranging from improving the quality of yields to protecting it from diseases. When choosing the right type of SRF for your plants, it’s a must to gather enough data about them and make the right choice. 

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