Misconceptions About Controlled—Release Fertilizers

Delivering and managing nutrition is one of the primary tasks associated with producing greenhouse crops. Most growers deliver nutrients using various water-soluble fertilizers, some growers use controlled-release fertilizers (CRF), while others use a combination of controlled-release and water-soluble fertilizers.

As I travel across the country to visit various growers, I’ve come to recognize that many growers would like to consider using controlled-release fertilizers at their facilities but do not understand these products well enough to implement them into their production systems.

With a shift in irrigation and fertility practices, where growers must control leaching and water runoff from their production sites, the use of controlled release fertilizers will allow growers to produce high-quality crops and manage the nutrients that leave their production sites more effectively.

From my perspective, there is a great need to educate growers of the benefits and risks associated with the use of controlled release technology. To help explain the many technical aspects of these products, I’ve teamed up with Goris Passchier from Northern Star Minerals (a division of Wilbur-Ellis Company) for this series of articles. Goris formulates controlled-release fertilizer formulations for growers based on a number of factors, as we will discuss, and helps growers achieve their nutritional goals. 

Pilon: What is a controlled-release fertilizer?

Passchier: The simple answer is, using various technologies, the water-soluble fertilizers you are accustomed to have been modified to slow the release characteristics of the nutrients.

The long answer is we need to make a definition clarification between what is called slow-release fertilizer (SRF) and controlled-release fertilizer (CRF). There is no official differentiation between slow-release and controlled-release fertilizers. Also, the Association of American Plant Food Control Officials (AAPFCO) uses both in its Official Terms and Definitions (AAPFCO, 1997).

However, we can make a simple differentiation, various products, such as Nitroform, Nutralene, Nitamin, Nfusion, NDemand, Coron, N-Sure and Nitro-30, are reacted urea formaldehyde products and are all considered SRFs. Each one has its own characteristic chain of polymers, which are gradually broken off by microbial activity and then made available for roots to uptake. Relatively speaking, the release characteristic of these products are similar regardless of the particle sizes or if they are in a liquid form. Growers should note that there are no slow release reacted phosphorous or potassium products. Most of these products are used in turf grass management and are not the main source of feed in the greenhouse or nursery trades.

The classification of controlled-release fertilizer should be reserved for encapsulated or coated materials. Just think of a coated M&M candy. You have an outer candy coating and the good stuff inside the coating. The same thing applies to CRFs. The outer coating protects the inner good stuff, called nutrients. Now, somehow we need to get the good stuff available to the plant’s root system in a timely manner so the plant can take it up as a nutrient. 

Pilon: How is fertilizer released?

Passchier: Controlled-release fertilizers that have an outer shell like an M&M candy are released by temperature, but moisture does need to be present. Let’s look at a urea nitrogen granule or prill with a guaranteed analysis of 46-0-0 that has been coated in some form or fashion. This coating protects the nutrients in the prill from releasing all at once.

The first thing that needs to happen is for the solid substance to get into a soluble form so it can get out of the prill. This is where moisture comes in. The moisture in the soil is drawn into the covered coated prill. This happens because the nutrients in the prill are in a salt form and water is drawn to salt. Once the water is drawn into the prill, the salt goes into a semi-soluble form (like the chocolate in an M&M candy that gets all gooey.) The rate the fertilizer becomes more soluble inside the prill is related to the temperature around the prill.

Thinking back to the M&Ms, when they are left in a cold refrigerator, you won’t be able to squeeze any chocolate out of them. If the candy is left on the counter at room temperature, you can squeeze some chocolate out of it. And when the candy is left on the hood of a car on a summer day, you more than likely will have a very gooey mess on your hands when you squeeze the candy, since the temperature made the candy very semi-soluble.

As water has entered the covered prill, pressure builds up on the inside and the ingredients in the prill need to get out. The release of nutrients varies depending on the technology used to formulate the coating. 

Pilon: I see there are several CRF products on the market. Do these products consist of the same technology?

Passchier: The basic principle with most CRF products is the same: taking a soluble form of fertilizer and coating it so you can have "controlled release." The technology of the coating and how that coating affects the release is what makes each CRF product somewhat different.

Some prills may crack open at different times so you get instant mini-releases. This form of release is usually characteristic of sulfur-coated products. Other prills begin to look like they are sweating as the salt moves from the inside through the coating membrane to the outside of the prill. Thicker coatings take longer for water to enter the prill. Consequently, the thicker the coating, the longer it takes nutrients to get out of the prill. This type of release is usually characteristic of polymer-coated products, such as Apex, Diffusion, Multicote and Polyon fertilizers.

Osmocote fertilizers use the words resin and polymers somewhat interchangeably. They are the oldest technology. What makes them different in a practical point is that the Osmocote prill swells in the pot where the other product lines show very little swelling of the prill. Whether this swelling of the prill is good or bad for growing plants should come from the grower’s experience with the products.

Another technology uses a parting agent in the coating, which creates micro-wicks that wick out the fertilizer from the inside to the outside of the prill.

With all CRF technology, it is important to remember that once the fertilizer gets out of the prill, it may only become available to microbes and root hairs, if it comes off the prill. There can be prills laying on the soil surface, moisture can be drawn from the soil and fertilizer can be released, but if it is stuck on the surface of the prill, it cannot be utilized as plant food. Consequently, moisture needs to move over the surface of the prill in order to wash the nutrients off the prill and into the root zone. With all CRF technology, it is important to place the prills where water can move over the prills, especially when using drip or micro-irrigation systems. 

Pilon: How are CRFs products similar and how do they differ?

Passchier: CRF products are similar in that soluble fertilizer is usually coated with either a resin or polymer coating. The difference between these products is how the soluble fertilizer comes out of the covered prill. This may occur by controlled cracking of the outer coating at different times, diffusion of nutrients through the semi-permeable membrane or with a chemical agent inside of the coating that acts as a wick.

With polymer-coated products, besides temperature, the thickness of the coating determines the rate nutrients are released. Combining or blending fertilizers with different thicknesses can be an effective method to predictably deliver nutrients to crops over time. Fertilizer blends consisting of various thicknesses give the fertilizer product a unique blueprint of release based on the temperature where the fertilizer is used. As a grower, these blueprints can be the key to your success or failure.

There are many factors growers must consider when deciding to implement controlled-release fertilizers into their production plans. Future installments of this series will discuss various nutrient sources, address numerous factors affecting the release and longevity of these products and help growers pull this information together allowing them to create appropriate and effective CRF programs.

Leave a Reply

More From Fertilization...
Giving Tuesday

November 24, 2015

Giving Tuesday On December 1 Is An Opportunity For The Industry To Make Charitable Tax-Deductible Donations

Organizations such as American Floral Endowment and others are encouraging industry members to participate in the generous spirit of the holiday season.

Read More
Cannabis marijuana

November 24, 2015

Five Florida Growers Receive Licenses To Potentially Produce And Process Medical Marijuana

The Florida Department of Health has announced the five nursery operations awarded with exclusive licenses to grow, process, and dispense “Charlotte’s Web,” a low-THC (non-euphoric) cannabis approved for patients with intractable epilepsy and people with advanced cancer.

Read More
Random Acts Of Flowers

November 24, 2015

Random Acts Of Flowers Partners With FTD And Pro Flowers To Make Milestone Charitable Bouquet Delivery

The organization, which recycles and repurposes flowers with a volunteer team that delivers bouquets to health care facilities across the country, made its 100,000th delivery to a health care facility in Chicago.

Read More
Latest Stories
Fertilizer Rates Feature Image

August 12, 2015

Selecting Fertilizer Rates For Several Spring Bedding P…

Fertilizing bedding plants can be difficult due to the differing needs of the large variety of plants that we grow. Many operations do not grow enough of any one crop to cater the fertilizer specifically for each crop. Therefore, grouping crops with similar fertilizer requirements and having two to three fertilizer strengths available is a practical way to ensure plants are getting the fertilizer they need. With many new plant varieties on the market, we wanted to conduct a trial at Cornell University to determine best fertilizer rates for several common bedding plant crops. 22 Bedding Plants Studied To Establish Fertilizer Rates Plugs and rooted liners of 22 crops (Table 1) were transplanted into 4-inch (500 mL volume) round pots with a commercial peat/perlite based substrate. The plants were grown in a glass greenhouse at Cornell University during the spring season at a spacing of one plant per square foot. Heating set […]

Read More

June 13, 2015

UMASS Fertilizer Trials Recommend Nature’s Source Organ…

In a recent online fact-sheet at its Extension website, the UMass Amherst Center for Agriculture, Food and the Environment lists Nature’s Source Organic Plant Food 3-1-1 as “the best liquid organic fertilizer,” according to Dr. Douglas Cox, Stockbridge School of Agriculture. It is called-out by the Extension after a number of years of studying the use of organic fertilizers for growing commercial greenhouse crops. The trials evaluated traditional water soluble and granular slow-release chemical fertilizers. Dr. Cox recommends Nature’s Source Organic Plant Food 3-1-1 as a liquid fertilizer that is readily available, cost effective, OMRI-listed and with good label directions for greenhouses. He also mentions the ease-of-use in how it mixes well with water and can pass fertilizer injectors. “Nature’s Source is currently the best liquid organic fertilizer,” Cox wrote in his article “Organic Fertilizers – Thoughts on Using Liquid Organic Fertilizers for Greenhouse Plants,” “I have seen no foliar chlorosis yet with this fertilizer. Nature’s source is widely available and a great […]

Read More

January 9, 2015

6 New Fertilizer Products For Healthy Plants

These five products add even more options for delivering nutrients to the root zone.

Read More

January 7, 2015

Fertilizers And The Future

As growers look for new ways to cut costs and conserve resources, fertilizer and equipment companies are offering products that strive to save water, reduce toxic runoff and keep chemicals out of the equation.

Read More

December 31, 2014

Gain Greater Control Of Fertilizer With Automated Ferti…

University researchers look at integrating irrigation and fertilization with the help of water sensors to reduce fertilizer treatments and improve application timing.

Read More

October 30, 2014

Basics & Beyond: Comparing Substrate Fertilizer Ame…

Cornell University researcher determines if substrate-incorporated slow-release fertilizers can be used to replace or reduce the need for liquid fertilizer for four spring crops.

Read More

July 24, 2014

Using Controlled Release Fertilizers To Produce Garden …

Researchers determined whether or not garden mums can be grown with controlled-release fertilizer, and if it reduces fertilizer leaching, as compared with water-soluble fertilizers.

Read More

March 14, 2014

New Foliage Pro Fertilizer Offers Complete Nutrition Pl…

Dyna-Gro Nutrition Solutions has developed a process it says is capable of keeping all 16 essential plant nutrients in solution form.

Read More

January 30, 2014

OASIS Grower Solutions Introduces New One-Bag Hydroponi…

The new 16-4-17 Hydroponic Fertilizer from OASIS Grower Solutions (OGS) is a one-bag solution that replaces two-part systems traditionally used by commercial hydroponic growers. It is specifically formulated for commercial hydroponic production of lettuce, herbs and vegetables.

Read More

December 30, 2013

Fertilizer Changes Growing Mix pH

When considering a fertilizer's influence on media pH, you need to know its acid or basic reaction.

Read More

December 30, 2013

Basics & Beyond: Fundamentals Of Phosphorus Nutriti…

Phosphorus is an essential element, after all.

Read More
Everris Liquid S.T.E.M.

December 30, 2013

New Fertilizers For 2014

New fertilizer products not only deliver optimum nutrition, they also provide for easier application and increased efficiency. Check out these new products to help your operation produce a healthy crop in 2014. Click through on the pages below.

Read More

December 18, 2013

Focus On Fertilizer: Micronutrients And Organics

New fertilizer products are focusing on micronutrients and providing efficient options for organic production.

Read More

August 27, 2013

BioWorks Adds EcoVita To The Verdanta Family Of Biofert…

EcoVita, a homogeneous granular organic fertilizer, has been added to Bioworks Inc.’s Verdanta biofertilizers product family. This fertilizer will be manufactured and supplied to BioWorks by DCM Corporation of Belgium, a producer of natural and organic-based fertilizers in Western Europe. EcoVita is suitable for a wide variety of crops with its gentle release curve including:• Organic fertilization as a base nutrition in potting mixes• Leafy vegetables• Fruiting vegetables (s a top dressing) • Roses and other ornamentals The new fertilizer offers long-lasting and continuous action for 75 to 100 days and contains organic phosphorus (5 percent P2O5) for fast rooting. Nutrients in EcoVita are gradually released by the soil microbes, in addition to producing humus for better rooting and less leaching. EcoVita is OMRI Listed, making it suitable for use in organic production. “We’re pleased to introduce EcoVita 7-5-10 as our organic NPK product to complement our organic products: K-Vita 2-0-20 […]

Read More

April 29, 2013

Rockwell Farms Introduces Ready-To-Pour Container Ferti…

Rockwell Farms has introduced Rockwell Farms Plant Food, a bottled liquid fertilizer that does not need to be diluted before use. Always looking for ways to help the consumer succeeed, Jason Roseman of Rockwell Farms says the operation is also always looking for ways to get consumers to come back and buy more plants and flowers. “We feel like fertilization is one of those things that can be very confusing,” Roseman says. “Not everyone does it, and not everyone knows what they’re supposed to do.” The solution: Rockwell Farms Plant Food. The formulation is 150 ppm of a 20-10-20 fertilizer and is sold in 24-ounce bottles. Rockwell recommends that one bottle be used to fertilize 1.5- to 3-gallon outdoor plant and flower containers every 21 days. The product’s signage shows a young patio gardener pouring the bottled fertilizer on a windowbox with the tagline, “Just pour on your way out […]

Read More

April 29, 2013

Plant Products To Be Purchased By MGS Horticultural And…

MGS Horticultural Inc., a full-service supplier of fertilizers, pest control products, seeds and substrates in North America, together with Haifa Chemicals, a global supplier of potassium nitrate for agriculture and industry, specialty plant nutrients and food phosphates, today announced a plan to purchase Canadian fertilizer and pesticides supplier Plant Products Co. Ltd. The deal is anticipated to close by the end of June 2013. MGS will acquire Plant Products’ Canadian distribution business, sales force and name. MGS plans to use both names (MGS Horticultural and Plant Products) in all communications going forward. MGS will maintain locations in Leamington, ON; Brampton, ON; Laval, QC; St. Hyacinthe, QC; and Detroit, Mich. As part of the deal, MGS has signed multi-year agreements with Haifa to maintain exclusive distribution of Plant-Prod Soluble Fertilizers, Acer Controlled Release Fertilizer, Stim-Root and potting soil premix fertilizers for distribution in Saskatchewan, Manitoba and Eastern Canada. “MGS is excited […]

Read More

March 19, 2013

Irrigation And Fertilizer Tips For New Vegetable Grower…

Compared to other variable costs, fertilizers are not the largest part of the budget in conventional greenhouse production. Nevertheless, over the course of the season, mistakes in fertilizer use can lead to significant damages or crop losses. That makes this an important topic for ornamental growers who are experimenting with growing vegetable crops. This article will emphasize major differences between fertilizers used in vegetable production and in ornamentals production. The different nutrition strategies, monitoring and water volume per plant will also be explained. Fertilizer In ornamental production, nutrients are delivered using various water-soluble fertilizers through a fertilizer injector, through the use of controlled-release fertilizers, or a combination of the two. There are numerous fertilizer mixes available with all the needed nutrients already included. The fertilization rate is often given in parts per million (ppm) of nitrogen (N), which is a way of expressing the fertilizer concentration. At younger stages, plants will […]

Read More

March 11, 2013

Daniels Plant Food Rebranded As Nature’s Source

Ball DPF has announced the launch of Nature’s Source, a rebranding in name and packaging for its seed extract-based plant fertilizer product Daniels Plant Food. The new brand will make its industry debut at California Spring Trials. “While we are proud of our heritage, we made this bold decision because we’re expanding sales to our existing market segments and entering new ones. It was a good opportunity to start with a fresh name and a modern look for all our products and packaging,” says Chance Finch, general manager for Ball DPF. “We wanted to make it obvious, beginning with our Nature’s Source brand name, to know our products are sourced from nature. Growers, contractors and gardeners can be confident that our effective and unique formulations remain unchanged. We’re excited about launching updated packaging for all our products, and especially the new ready-to-spray plant food for home gardeners.” The Nature’s Source brand […]

Read More
[gravityform id="35" title="false" description="false"]