What is a controlled release fertiliser?
As professional growers will appreciate, a lot of hard work goes into creating the environment that container nursery stock, perennials, pot plants and bedding plants require. Fortunately, controlled release fertilisers (CRFs) offer a convenient way of helping them to achieve this aim by ensuring that their plants gain the right kind of nutrition at the right time.
Whilst such useful products may seem like a fairy tale, they are in fact a very real result of applied science and innovative technology. Andrew Wilson is technical manager for ICL Specialty Fertilizers, which produces the established CRF brand Osmocote. He explains how CRFs work. "A controlled release fertiliser is a granule containing nitrogen, phosphorus and potassium (NPK) – and, depending on the product, they can also contain magnesium and other trace elements. These are then covered in a coating."
He notes that Osmocote features an organic, resin, semi permeable coating and adds: "As water penetrates through the coating it dissolves the nutrients inside the granule. The osmotic pressure inside the granule releases the dissolved nutrients through the coating. It sucks water in because it’s very concentrated inside – and then, as the pressure builds up, it pushes out the fertiliser through the coating." CRFs are also influenced by temperature. Wilson explains: "They are temperature related. The only thing that affects the release [of the fertiliser] is the temperature. The warmer it gets the more it releases. That’s the basics of it. It’s not affected by pH levels, salinity, water quality and rain."
Wilson adds that, when all the nutrients have been released, the resin coating breaks down gradually. Higher temperatures will speed up the nutrient release and therefore shorten the product’s longevity whilst lower temperatures will slow down the release of nutrients and extend longevity. Cleverly, this means that the plants are getting the nutrients they need for the conditions they are experiencing.
Osmocote – a "finely-tuned" product
There are several CRFs available in the marketplace utilising various coating technologies and featuring different nutritional formulations. ICL usefully offers the industry a range of different Osmocote products for ornamental crops of many shapes, sizes and species.
This year, the brand celebrates its 50th anniversary. Wilson says: "We are constantly developing our products and over the years we’ve constantly improved them. We have been making Osmocote since 1967 so that was the first generation product – a coated NPK granule. And then we produced a second generation product – Osmocote Pro, which added trace elements and various longevities of release."
Wilson explains that CRFs are calibrated products:
"The thickness of the coating reflects how fast the fertiliser will release. For example, a 3-4 month product will have a very thin coating, while a 12-14 month product will have a thicker coating. It’s the thickness of the coating that gives it the longevity." Osmocote products therefore offer growers a choice of longevities. For example, Osmocote Pro includes NPK, magnesium and other key trace elements (the micronutrients that the plant requires in small amounts) and is available in several longevities, from 3-4 months up to 12-14 months.
Whilst second generation products like Osmocote Pro have an efficient release of nutrients. ICL’s third and fourth generation products are even more finely-tuned. The third generation, Osmocote Exact, features patterned release technology, which gives a guaranteed release pattern due to its unique production process and extended quality control process. It features a blend of Osmocote prills (granules) formulated to release at different rates (faster or slower) throughout the growing season. This steady and continuous nutrient release ensures crop safety and ensures nutrients are available when the plant needs it.
Osmocote Exact Double Coating Technology (DCT) is the fourth generation featuring programmed nutrient release, when ICL can actually specify the release pattern that the grower needs. An understanding that, after potting, a young plant’s nutrient demand is initially quite low – but is much higher after establishment, has led to the development of a unique Double Coating Technology (DCT).
These coatings have a different composition to the original resin coating and they work by postponing the product’s start-up by up to three months (compared to Osmocote’s traditional release start-up of one or two weeks.) Osmocote Exact Hi.End features, typically, 25% DCT coated granules where a second coating delays the nutrient release by six weeks (or up to three months depending on the longevity). This gives a release pattern which is 25% lower initially but with a higher release later just when the plant’s nutrient demands are highest. This is one of ICL’s key products, and Osmocote Exact Hi.End grows the highest quality plants by matching plant nutrient demand and minimising leaching of nutrients.
Moreover, further Osmocote Exact DCT development sees products such as Osmocote Exact Protect have a second coating added to 100% of the prills, postponing the product’s start-up by up to three months. As such product can be applied at potting stage in the winter months, but will not release until the growing season has started, meaning that potential leaching and wastage is limited. "So it gets very technical," asserts Wilson.
Not surprisingly, the process of creating Osmocote is so specialist that, reveals Wilson, "we have only got two factories in the world – one in Holland, one in the United States. They each have probably half a dozen coating lines each." Admittedly it is fascinating to consider the journey that CRFs make – from a factory assembly line across the seas all the way into a plant pot – but if they help growers to produce colourful plants that delight their customers it is arguably worth the effort.