What Is Controlled Release Fertilizer?

One of the main concerns of greenhouse and nursery production systems is the high nutrient losses that come with using certain fertilizers, particularly water-soluble ones. This is why using controlled release fertilizers (CRF) has become a practical alternative in maximizing nutrients. But first, you need to know how this fertilizer works and how it can contribute to crop yield and quality.

Controlled release fertilizer is a variety of fertilizers designed to gradually release into the soil in a controlled manner. Because of this, plants get provided with available nutrients for a longer time. The release date of the fertilizer is dictated by the thickness of the coating and the air temperature. The greater the temperature, the faster the fertilizer gets released. The rate of release is designed in a synchronized pattern to meet changing crop nutrient requirements.

To decide if CRF is the best option for your crops, you need to know how it works and the benefits of using it.

Factors That Determine the Release of Controlled Release Fertilizers

The formulations of CRF are often developed in NPKs – N (Nitrogen), P (Phosphorus), and K (Potassium) or other micronutrients such as Mg (Magnesium), Ca (Calcium), Zn (Zinc), Cu (Copper), Fe (Iron), B (Boron) etc. combination and release pattern. It’s designed to match the primary nutritional needs of your plants during the growing season to promote the best results and develop the plants consistently without deficiencies.

The longevity of the release of a CRF will depend on how thick the polymer coating is. A CRF with a 3-4 month release can be extended up to 9 months just by increasing the thickness of the coating. Keep in mind that as the longevity of the release increases, so does the required application rate. So if a CRF with a 3-4 month release has an application rate of 6 lbs/cu yd, it can increase to 9 lbs/cu yd with a release time of 8-9 months. 

Temperature has the greatest influence on the release of these fertilizers. CRF works best at normal temperatures, but it shouldn’t drop below 50˚F (10˚C) or go beyond 90˚F (32˚C). If the temperature is too low, it will not trigger the fertilizer to release; too high, and it can release too much. 

Moisture plays a significant part in the release as well. If a growing medium gets all dried up, the amount of fertilizer released can be significantly reduced. Other factors such as soil composition and PH-value, rain, irrigation, and bacterial life play no part in the longevity of CRF.

Why Use Controlled Release Fertilizers

Using CRF has three main advantages. First, it can make nutrient management simpler as compared to the repeated applications needed for water-soluble fertilizers. Second, you can use nutrients for your plants more efficiently with CRF. Third, using this fertilizer can enhance the overall performance of your crops.

CRF supplies nutrients to your plants for a long time. For greenhouse crops, you may not have to worry about re-applying fertilizers for the entire production cycle. Just put the prills to the mix before planting, and that’s pretty much it. There’s no need for water-soluble fertilizer equipment, and you only tap water for irrigation. Because the nutrients are slowly released throughout the season, fewer nutrients are lost in the leachates. The nutrients are retained in the substrate to be absorbed by the plants as they develop roots.

Benefits of Controlled Release Fertilizers

There are five main reasons why many growers like to use CRF:

  • You will need less fertilizer – since the release of available nutrients in CRF complements the plant uptake, it means there is less fertilizer loss and reduces application rates up to 30%, which is definitely considerable as compared to traditional liquid or granular fertilizers.
  • The application is simple – you just apply CRF directly into the soil, no complicated dosing or injection system needed.
  • It saves time and effort – you only need to apply CRF once to cover the nutritional requirements of your crops throughout the growth cycle. This means savings in terms of costs and labor involved in fertilizer application. As a grower, you don’t need to spend much time on fertilization and therefore allows you to focus on other growth requirements.
  • You optimize your plant’s development – the controlled release of the fertilizer gives your plants the balanced nutrition needed throughout the growth cycle. This contributes to high-quality yields.
  • It’s environment-friendly – environmental contamination is prevented since the nutrient loss is minimized.

How To Start Using Controlled Release Fertilizers

Starting small is the sensible way if you have limited experience with using CRF. What you should do is select a crop or a portion of it and then familiarize yourself with the new cultural practice. Afterwards, expand gradually to more crops and areas. Make sure to start with the lowest rate listed on the fertilizer label for a given container size or crop. If you have questions, just consult your fertilizer seller.

How To Store Controlled Release Fertilizers

Your CRF stocks should be kept in a dry environment and stored indoors, preferably on a concrete pad with a curb to prevent any leaks and spills. The storage should be kept moist-free, especially when the fertilizer bags have already been opened. Only move the bags when necessary – the prills are prone to cracking and should be handled with care.

If you have already blended the CRF into the growing mixes before use, you can’t store these mixes anymore. Use them as soon as possible to keep the prills from absorbing water and prevent nutrient loss.  

Whether it’s CRF or the water-soluble type, the best type of fertilizer you should use should be based on the requirements and resources of your growing operation. Both methods have their own set of pros and cons, and this is why you should consider other factors – such as time of the year, climate, and amount of time spent on fertilizer application and control – in choosing the right fertilizer for your plants.

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