Is controlled release fertiliser the same as slow release?

Introduction

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Plants require essential nutrients such as nitrogen, phosphorus, and potassium to grow and thrive. However, these nutrients are often not present in sufficient quantities in the soil, which can hinder plant growth and productivity. This is where fertilizers come in. Fertilizers are substances added to the soil to provide plants with the necessary nutrients for optimal growth and development.

While traditional fertilizers provide an immediate boost of nutrients to plants, slow-release and controlled-release fertilizers have their unique benefits. Slow-release fertilizers gradually release nutrients over an extended period, while controlled-release fertilizers release nutrients in a more controlled manner based on environmental factors such as temperature and moisture.

In this article, we will delve into the differences between slow-release and controlled-release fertilizers, their benefits, and how to choose the right one for your specific needs. By understanding these concepts, you can improve the health and productivity of your plants while also saving time and resources.

Slow-release Fertilizers

Slow-release fertilizers, also known as timed-release or gradual-release fertilizers, release nutrients over an extended period, typically several months to a year. These fertilizers are designed to provide a steady supply of nutrients to plants without the risk of over-fertilizing or nutrient loss through leaching.

One of the key benefits of slow-release fertilizers is that they reduce the need for frequent applications. This can save time and resources, especially for large-scale agricultural operations. Slow-release fertilizers also help to maintain consistent soil nutrient levels, reducing the risk of nutrient deficiencies or excesses that can harm plant growth.

However, slow-release fertilizers do have some drawbacks. They are typically more expensive than traditional fertilizers, and the nutrient release rate can be affected by factors such as temperature, moisture, and soil pH. Additionally, slow-release fertilizers may not be suitable for plants with specific nutrient requirements or in situations where a quick nutrient boost is needed.

Controlled-release Fertilizers

Controlled-release fertilizers, also known as coated or encapsulated fertilizers, are designed to release nutrients over an extended period based on environmental factors such as temperature, moisture, and microbial activity. These fertilizers provide a more precise and targeted release of nutrients, reducing the risk of nutrient loss and improving overall plant health.

One of the key benefits of controlled-release fertilizers is their ability to provide a consistent supply of nutrients to plants over an extended period, which can improve plant growth and productivity. They also reduce the need for frequent fertilization, which can save time and resources. Controlled-release fertilizers are particularly useful for crops with specific nutrient requirements or in areas with high rainfall or leaching.

However, controlled-release fertilizers are generally more expensive than traditional fertilizers and may not be suitable for all crops or soil types. The release rate can also be affected by environmental factors such as temperature and moisture, which can impact the efficacy of the fertilizer.

Nitrification Inhibitors

Nitrification inhibitors are substances that can be added to fertilizers to slow down the conversion of ammonium into nitrate in the soil. By slowing down this process, nitrification inhibitors can reduce the risk of nitrogen loss through leaching and improve the efficiency of nitrogen uptake by plants.

Nitrification inhibitors can be used in combination with slow-release or controlled-release fertilizers to further improve nutrient use efficiency. These inhibitors are particularly useful in high rainfall areas or areas with sandy soils that are prone to nutrient leaching.

Some common nitrification inhibitors include nitrapyrin, dicyandiamide, and 3,4-dimethylpyrazole phosphate. ese inhibitors can be added to fertilizers in small amounts, typically 0.1% to 0.5% of the fertilizer weight.

While nitrification inhibitors can improve the efficiency of fertilizer use and reduce the risk of nutrient loss, they are not really slow-release fertilizers.

Comparison of Slow-release and Controlled-release Fertilizers

Slow-release and controlled-release fertilizers both provide a more controlled release of nutrients over an extended period, reducing the need for frequent applications and improving overall plant health. However, there are some key differences between the two types of fertilizers.

• Slow-release fertilizers provide a steady release of nutrients over an extended period, typically several months to a year. They are generally less expensive than controlled-release fertilizers but may not provide the same level of precision in nutrient delivery. Slow-release fertilizers can also be affected by environmental factors such as temperature, moisture, and soil pH.
• Controlled-release fertilizers release nutrients based on environmental factors such as temperature, moisture, and microbial activity. They provide a more targeted and precise release of nutrients, reducing the risk of nutrient loss and improving overall plant health. However, controlled-release fertilizers are generally more expensive than slow-release fertilizers and may not be suitable for all crops or soil types.

Types of Fertilizers that fit into these cateogies

Resin Coated Fertilizers

• Resin coated fertilizers are a type of slow-release fertilizer where the fertilizer granules are coated with a layer of synthetic resin.
• This coating allows for a gradual release of nutrients over an extended period, typically several months.
• Resin coated fertilizers provide a more precise nutrient release than traditional slow-release fertilizers and can reduce the risk of nutrient leaching and runoff.
• However, resin coated fertilizers are generally more expensive than traditional slow-release fertilizers and may not be suitable for all soil types.

Controlled-Release Fertilizers

• Controlled-release fertilizers are designed to release nutrients based on environmental factors such as temperature, moisture, and microbial activity.
• These fertilizers provide a more precise and targeted release of nutrients, reducing the risk of nutrient loss and improving overall plant health.
• Controlled-release fertilizers are particularly useful for crops with specific nutrient requirements or in areas with high rainfall or leaching.
• However, controlled-release fertilizers are generally more expensive than traditional fertilizers and may not be suitable for all crops or soil types.

Polymer-coated Fertilizers

• Polymer-coated fertilizers are a type of controlled-release fertilizer where the fertilizer granules are coated with a layer of polymer.
• The polymer coating allows for a gradual release of nutrients over an extended period, typically several months to a year.
• Polymer-coated fertilizers provide a more precise nutrient release than traditional slow-release fertilizers and can reduce the risk of nutrient leaching and runoff.
• However, polymer-coated fertilizers are generally more expensive than traditional slow-release fertilizers and may not be suitable for all soil types.

Nutrient Binding Fertilizers

• Nutrient binding fertilizers are a type of slow-release fertilizer that works by binding nutrients to soil particles, reducing the risk of nutrient loss through leaching.
• These fertilizers typically release nutrients over an extended period, ranging from several months to several years.
• Nutrient binding fertilizers are generally less expensive than other types of slow-release fertilizers and can be beneficial for crops with specific nutrient requirements or in areas with high rainfall or leaching.
• However, nutrient binding fertilizers may not be suitable for all crops or soil types.

Liquid Slow-Release Fertilizers

• Liquid slow-release fertilizers are a type of slow-release fertilizer that can be applied directly to plant foliage or soil.
• These fertilizers typically release nutrients over an extended period, ranging from several days to several weeks.
• Liquid slow-release fertilizers can be more convenient to use than other types of slow-release fertilizers and may be beneficial for crops with specific nutrient requirements.
• However, liquid slow-release fertilizers can be more expensive than traditional liquid fertilizers and may not be suitable for all crops or soil types.

Organic Slow-Release Fertilizers

• Organic slow-release fertilizers are a type of slow-release fertilizer made from organic materials such as bone meal, fish meal, or compost.
• These fertilizers provide a gradual release of nutrients over an extended period, typically several months to a year.
• Organic slow-release fertilizers are generally less expensive than synthetic slow-release fertilizers and can improve soil health and fertility.
• However, organic slow-release fertilizers may not provide the same level of precision in nutrient delivery as synthetic slow-release fertilizers and may be more suitable for certain soil types or crops.

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How to Apply Slow-release and Controlled-release Fertilizers

Slow-release and controlled-release fertilizers should be applied according to the manufacturer's instructions. They are typically incorporated into the soil during planting or applied as a top-dressing. It is important to calculate the correct amount of fertilizer needed based on soil type, crop type, and nutrient requirements to avoid over- or under-fertilization.

How to Choose Between Slow-release and Controlled-release Fertilizers

The choice between slow-release and controlled-release fertilizers depends on several factors, including soil type, crop type, and nutrient requirements. Slow-release fertilizers are generally less expensive and provide a steady release of nutrients over an extended period, while controlled-release fertilizers provide a more precise release of nutrients based on environmental factors.

It is important to consider the specific needs of your plants and soil conditions when choosing between slow-release and controlled-release fertilizers. Consulting with a professional agronomist or soil scientist can also be helpful in determining the best fertilizer type for your specific situation.

Frequently Asked Questions

1. How long does the nutrient release from slow-release and controlled-release fertilizers last?

• Slow-release fertilizers typically release nutrients over several months to a year, while controlled-release fertilizers release nutrients based on environmental factors over an extended period.

2. What factors affect the rate of nutrient release from slow-release and controlled-release fertilizers?

• Environmental factors such as temperature, moisture, and microbial activity can affect the rate of nutrient release from slow-release and controlled-release fertilizers.

3. How do I know if my crops are getting enough nutrients from slow-release and controlled-release fertilizers?

• Monitoring plant growth, soil nutrient levels, and crop yields can help determine if crops are receiving adequate nutrients from slow-release and controlled-release fertilizers.

4. Can slow-release and controlled-release fertilizers be used in all types of soil?

• Slow-release and controlled-release fertilizers can be used in most soil types, but it is important to consider the specific nutrient requirements of your crops and soil conditions.

5. Are slow-release and controlled-release fertilizers more expensive than traditional fertilizers?

• Yes, slow-release and controlled-release fertilizers are generally more expensive than traditional fertilizers due to their extended release period and precision nutrient delivery.

6. How should slow-release and controlled-release fertilizers be applied to crops?

• Slow-release and controlled-release fertilizers should be applied according to the manufacturer's instructions, typically during planting or as a top-dressing.

7. What is the difference between slow-release and controlled-release fertilizers?

• Slow-release fertilizers provide a steady release of nutrients over an extended period, while controlled-release fertilizers release nutrients based on environmental factors over an extended period.

8. Can slow-release and controlled-release fertilizers be used in conjunction with other fertilizers?

• Yes, slow-release and controlled-release fertilizers can be used in conjunction with other fertilizers to provide additional nutrient support.

9. Do slow-release and controlled-release fertilizers require different equipment or application techniques than traditional fertilizers?

• No, slow-release and controlled-release fertilizers can be applied using traditional fertilizer application techniques.

10. Are there any environmental benefits to using slow-release and controlled-release fertilizers?

• Yes, slow-release and controlled-release fertilizers can reduce the risk of nutrient runoff and leaching, reducing the environmental impact of fertilizer use.

Conclusion

Slow-release and controlled-release fertilizers provide a more controlled and precise release of nutrients over an extended period, improving plant growth and productivity. While these fertilizers are more expensive than traditional fertilizers, their benefits can outweigh the cost for many growers. By considering soil type, crop type, and nutrient requirements, growers can choose the right slow-release or controlled-release fertilizer for their specific needs, ultimately improving plant health and productivity while reducing environmental impact.

Do you know the difference between slow-release and controlled-release fertilisers?

Although these terms are sometimes used interchangeably, the terms 'slow-release fertiliser' (SRF) and 'controlled-release fertiliser' (CRF) strictly do not mean the same thing &#; even though both do release plant nutrients at a slower rate than when highly-soluble conventional or 'straight' fertilisers are used.

For those who are unclear of these differences, we hope that the following simplified explanation of these distinctions will be both interesting and informative &#; and explain how each of these two classes of fertiliser releases plant nutrients.

So what are 'Slow' Release Fertilisers?

Slow-release fertilisers (SRFs), unlike controlled-release fertilisers, are not encapsulated in coated prills. The most commonly used slow-release fertilisers supply nitrogen (N) at a slower rate than if a readily-soluble source of nitrogen were applied (e.g. ammonium sulphate, ammonium nitrate or urea). In one of the methods to achieve this, fertiliser manufacturers synthesise what is known as long-chain molecules by chemically combining a nitrogen-source molecule with an aldehyde &#; for example, urea-formaldehyde or methyl urea. The delayed release of nitrogen is achieved by microbial action in the growing medium &#; slowly breaking down the long-chain molecules and eventually converting the resulting ammonium nitrogen to nitrate (the form of nitrogen that plant roots can take up).

Other forms of slow-release nitrogen (e.g. IBDU) differ in composition and modes of action. However, the above example explains the concept of a slow-release fertiliser compared with a controlled-release fertiliser (which we will explain below).

It should be emphasised that the duration of release in a slow-release fertiliser cannot be controlled because the effectiveness of the microbial organisms in molecular breakdown is dependent on other factors &#; including the nature of the growing medium, its moisture level and temperature. Also, a release time extending beyond two or three months cannot be expected.

(As an interesting aside, animal manures, composts and 'green manures' could be deemed slow-release fertilisers, providing many benefits in soil improvement. However, their nutrient chemistry is complex, and microbial activity is still necessary to slowly convert the organic substances into minerals that plants can use. Plant roots don't absorb manure &#; as such! After all, nitrate (NO 3&#;) derived from manure by microbial action (nitrification) is exactly the same as NO3&#;  in a mineral fertiliser!)

So what are 'Controlled Release' Fertilisers?

Controlled-release fertilisers (CRFs) differ fundamentally from (SRFs) in both technology and mode of nutrient release. Soluble essential plant nutrients, individually or in various homogeneous blends (depending on the application), are encapsulated in an organic resin or polymer coating to form prills. This coating is the secret of the delayed release of nutrients in a CRF. The physical processes by which this is achieved are explained in simplified terms below.

It should be emphasised that the term 'controlled' implies a much greater degree of control in the rate, pattern and duration of nutrient release than can be achieved using SRFs.

The principles behind the success of CRFs were first employed several decades ago. Subsequent technological advances and refinements have led to a range of well-known brands of CRFs &#; for example, Osmocote, Nutricote, Plantacote, Floracote, Multicote, Basacote and Macracote.

Now let's explain how a CRF works:  The coating on the prills acts as a selectively-permeable or semi-permeable membrane &#; a barrier to some molecules but allowing specific different molecules to pass through. When a CRF is applied to an adequately-moist growing medium, there is a one-way passage of water through the coating to the inside of the prill. This phenomenon is called 'osmosis'. The absorbed water partially dissolves the mineral nutrients inside the prill to create a highly-concentrated solution. This then increases the hydrostatic pressure within the capsule. No more water will enter when the hydrostatic pressure becomes equal on both sides of the capsule.

How, then, does the fertiliser get out into the growing medium? This is attributable to another phenomenon known as 'diffusion' (the movement of molecules from a liquid of higher concentration into a liquid of lower concentration). Again the key lies in the coating structure, which contains minute micropores. When the plants are watered, the hydrostatic pressures become unequal inside and outside the capsule, and a small amount of dissolved nutrient moves out, by diffusion, through these micropores into the growing medium.

• The rate of nutrient release in a CRF is, in most cases, temperature-related. An increase in temperature causes the micropores to expand in width, allowing more nutrients to diffuse; remember, this is not osmosis but diffusion. (Osmosis is water in, diffusion is nutrient out.) The nutrients are then dispersed within the growing medium (also by diffusion) &#; coupled with the percolation of dissolved nutrients when the plants are watered. We should regard this correlation between increased nutrient release and increasing temperature as a critical redeeming feature of a CRF: Cooler weather generally means slower plant growth and lower nutrient demand. This lower demand correlates with the reduced rate of nutrient release. Conversely, as temperatures rise, growth increases &#; demanding more nutrient. This is precisely what happens in the temperature-related release pattern of CRFs!
• The duration of nutrient release is governed in most cases by the thickness of the coating &#; although a few manufacturers use some other technologies. Products have been developed which offer release times ranging from 2 to 24 months.
• A range of 'patterned' releases can be achieved in a product by blending a mixture of prills with differing release rates or formulae &#; designed to synchronise with specific nutritional requirements during a growth cycle.

What are the Benefits of using SRFs and CRFs?

The significant benefits of using slow- or controlled-release fertilisers over readily-soluble 'straight' fertilisers include:

• Slower release rates mean longer-term feeding and minimal nutrient wastage through leaching
• A high degree of control over release rates, duration and pattern (CRFs only) means better synchronisation of nutrient release with demand.
• Improved plant growth and health (plants get what they need as they need it)
• Reduced frequency of application, with associated lower labour costs
• Environmental benefits (minimal nutrient in leachate, reducing freshwater/marine contamination
• Minimisation of concentrated nutrient build-up &#; a risk for high salinity-related root and leaf burn.

There is now a trend to transfer these benefits, long-proven for container-grown stock, to field crop production by changing to slower-release fertilisers &#; especially where environmental concerns are an issue.

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