Controlled-Release and Slow-Release Fertilizers as ...

Dec. 30, 2024

Controlled-Release and Slow-Release Fertilizers as ...

Nutrient management is closely associated with fertilizer type, application rate, application time, and application placement. For example, blueberry plants prefer ammoniacal nitrogen rather than nitrate nitrogen for their growth and development. However, most crops use both ammoniacal and nitrate nitrogen. Proper nutrient management should include the 'Four R's' of fertilizer use: apply the right nutrient, at the right rate, at the right time, and in the right place for the selected crop (Mikkelsen ). In Florida, there is another R, i.e., the 5th R, the right irrigation, please read https://edis.ifas.ufl.edu/publication/CV296 for more details (Liu et al. ). This article focuses on how to select the right fertilizer to enhance profitability and satisfy best management practices (BMPs). There are many fertilizer sources available for commercial crop production. The characteristics of each fertilizer type determine whether its use poses an advantage or a disadvantage to a farmer. This article provides a general overview on quick- and slow-release fertilizers for commercial crop producers, crop consultants, crop advisers, UF/IFAS Extension faculty, researchers, and students who are interested in nutrient management for commercial crop production.

If you want to learn more, please visit our website Sanyuanjiuqi.

Most used commercial fertilizers are water-soluble quick-release fertilizers (QRFs) that are predictively readily available for plants when properly placed in soil. Quick-release fertilizers are ideal for pre-plant applications, side dressing, hydroponics, or fertigation for many crops, including vegetables. They are highly practical if nutrient leaching or immobilization of nutrients by soil particles is not a serious concern (Wolf ), especially if unpredictable, high-leaching/flooding events do not occur. If conditions are favorable, less expensive QRFs have proven to be effective in crop production.

In the best conditions, QRFs become available to plants at a consistent rate (Trenkel ). They will release all readily available nutrients in a short period of time after being properly applied to soil with appropriate soil moisture. In other words, their release curve is immediate and does not synchronize with or match the dynamic needs of crop growth, which is why applying timely side dressings is necessary. In fact, crop nutrient requirements change as plants develop. For example, snap bean (Figure 1) has a slow-fast-slow growth stage pattern that has a smaller nutrient requirement in the early stage, a greater nutrient requirement in the middle stage, and a smaller nutrient requirement again in the late stage. Traditionally, multiple fertilizer applications, or side dressings, have been used to accommodate plant nutrient demand, minimize nutrient losses, and increase fertilizer use efficiency. Using too much fertilizer all at once without timing applications to the plants' growth stage pattern can expose plants to burning and cause nutrient loss through leaching or runoff. It frequently means that nutrients will not be available to plants when they need them. To deal with these challenges, the global fertilizer industry has been working to develop new fertilizers called controlled-release fertilizers (CRFs) and slow-release fertilizers (SRFs). These fertilizers have become more and more popular in recent years (Robbins ).

Controlled-Release Fertilizers

The Association of American Plant Food Control Officials defines CRFs as fertilizers that contain a plant nutrient in a form the plant cannot immediately absorb. Uptake is delayed after application, so that CRFs provide the plant with available nutrients for a longer time compared to QRFs, such as urea.

Controlled-release fertilizers are typically coated or encapsulated with inorganic or organic materials that control the rate, pattern, and duration of plant nutrient release. Polymer-coated urea exemplifies CRFs (Du et al. ; Loper and Shober ). These fertilizers control the release of nutrients with semi-permeable coatings, occlusion, protein materials, or other chemical forms, by slow hydrolysis of water-soluble, low-molecular-weight compounds, or by other unknown means (Trenkel ). Most importantly, the release rate of a CRF fertilizer is designed in a pattern synchronized to meet changing crop nutrient requirements.

As required by Florida rule, at soil temperatures below 77°F, a CRF must meet the following three criteria: (1) less than 15 percent of the CRF nutrients should be released in 24 hours, (2) less than 75 percent should be released in 28 days, and (3) at least 75 percent should be released by the stated release time (40'360 days) (Trenkel ).

Slow-Release Fertilizers

Nitrogen products decomposed by microbes are commonly referred as SRF fertilizers. Some SRFs such as N-SURE are made in factories. However, some such as manure are naturally originated and cannot be formulated to permit controlled release (Liu et al. ). The nutrient release pattern of SRFs is fully dependent on soil and climatic conditions. Slow-release fertilizer releases nutrients gradually with time, and it can be an inorganic or organic form. An SRF contains a plant nutrient in a form that makes it unavailable for plant uptake and use for some time after the fertilizer is applied. Such a fertilizer extends its bioavailability significantly longer than QRFs such as ammonium nitrate, urea, ammonium phosphate, or potassium chloride.

Nitroform (also referred to as trinitromethane with a chemical formula HC[NO2]3) exemplifies inorganic SRF fertilizers (Loper and Shober ). Urea-formaldehyde (UF), urea-isobutyraldehyde/isobutylidene diurea (IBDU), and urea-alcetaldehyde/cyclo diurea (CDU) typify organic SRF fertilizers (Trenkel ). Based on the source, there are two types of SRF fertilizers: natural and artificial (Table 1).

Natural SRFs include plant manures, such as green manure or cover crops, all animal manures (chicken, cow, and poultry) and compost (Shukla et al. ). Because of their organic nature, these must be broken down by microbial activity before the nutrients can be released to crops. In general, organic fertilizers may take a long time to release nutrients, and these nutrients may not be available when the plant needs them. The duration of nutrient release of this type of organic fertilizers mainly depends on soil microbial activity that is driven by soil moisture and temperature. Organic SRFs contain both macro-nutrients (nitrogen, phosphorus, potassium, etc.) and micro-nutrients (iron, manganese, copper, etc). The nutrient concentrations of organic SRFs are relatively lower than those of synthetic SRF fertilizers. For example, Sup'r Green brand is a chicken manure fertilizer containing only 3-2-2 % N, P2O5, and K2O, respectively.

Synthetic SRFs are sparingly water-soluble. The bioavailability of this type of fertilizers (typically in pellet or spike form) depends on soil moisture and temperature. Nutrients are released throughout a period of time that may range from 20 days to 18 months (Trenkel ). Therefore, fewer applications are needed with SRFs, but nutrients are released based upon the temperature and moisture conditions in the soil, which may not match the crop growth demand due to varying weather conditions (Trenkel ). Synthetic SRFs often contain a single nutrient at a much higher level than would occur in a natural SRF. For example, N-Sure® is a SRF that contains 28 percent nitrogen (28-0-0) (Clapp ; Liu and Williamson )

The Difference between Slow- and Controlled-Release Fertilizers

The terms "slow-release fertilizer," or SRF, and "controlled-release fertilizer," or CRF, do not mean the same thing.
Controlled-release fertilizer is also known as controlled-availability fertilizer, delayed-release fertilizer, metered-release fertilizer, coated fertilizer (Oertli and Lunt ), or slow-acting fertilizer (Gregorich et al. ). According to Shaviv (), "The term controlled-release fertilizer became acceptable when applied to fertilizers in which the factors dominating the rate, pattern and duration of release are well known and controllable during CRF preparation."
Slow-release fertilizers involve a slower release rate of nutrients than conventional water-soluble fertilizers, but the rate, pattern, and duration of release are not controlled (Trenkel ) because they depend on microbial organisms whose effectiveness is dependent on soil temperature and moisture conditions.
Because of their dependence on microbial digestion to enable nutrient availability, SRFs occasionally pose the risk of increased harmful leaching events. This situation occurs when favorable conditions for microbial activity follow after the cropping cycle. Excess available nutrients can be pollutants irrespective of the source.

Advantages of Using CRFs and SRFs

The major advantages for using SRFs or CRFs include:

Decreased nutrient losses and enhanced nutrient-use efficiency. The application of CRFs and SRFs can potentially decrease fertilizer use by 20 to 30 percent of the recommended rate of a conventional fertilizer while obtaining the same yield (Trenkel ).
Minimization of fertilizer-associated risks such as leaf burning, water contamination, and eutrophication (a process where water bodies receive excess nutrients). The slow rates of nutrient release can keep available nutrient concentrations in soil solution at a lower level, reducing runoff and leaching losses.
Reduced application and labor costs. For example, in current practices, commercial potato producers use 3 to 4 applications of nitrogen fertilizers for northeast Florida and 2 applications for southwest Florida (personal communication with local potato producers). Eliminating extra applications of fertilizer saves the farmer between $5 and $7/acre broadcasting expense (Liu et al. ). Additionally, avoidance of fertilizer application in late growth stage eliminates plant damages to crops.
Better understanding of nutrient release rate and duration (CRFs only, because they are less sensitive to soil and climate conditions) (Shaviv ; Shoji ; Trenkel ). Knowing when to apply fertilizer and in what quantities saves money, reduces fertilizer-associated risks to crops and the environment, and improves nutrient management programs.
Lowered soil pH in alkaline soils for better bioavailability of some nutrients. Applying sulfur-coated urea will probably increase soil acidity because both sulfur and urea contribute to increasing the acidity (lowering soil pH) of the soil. Consequently, phosphorus or iron may be more bioavailable and benefit some crops like blueberry, potato, and sweet potato (Liu and Hanlon ). In addition, sulfur is an essential nutrient for all crops.
Reduced production costs if there is an abundant supply of SRF sources like manures nearby.

Disadvantages of Using CRFs and SRFs

Most coated or encapsulated CRFs and SRFs (Tables 1 & 2) cost considerably more to manufacture than conventional fertilizers. This extra cost increases growers' crop production costs. For example, the price was $650 per ton for environmentally smart nitrogen (ESN) (44% N) versus $481 per ton for urea (46 percent N) (Ruark ). Environmentally smart nitrogen was 35.1 percent more costly than urea. The price per unit of nitrogen was 41.3 percent greater for ESN than for conventional urea.
Applying sulfur-coated urea almost always lowers soil pH as aforementioned. However, this acidification may cause nutrient disorders such as calcium deficiency or magnesium deficiency if there is not a proper nutrient management program.
Nutrient deficiencies may occur if nutrients are not released as predicted because of low temperatures, flooded or droughty soil, or poor activity of soil microbes.
Possible uncontrolled nutrient release of SRFs. Use efficiency of SRFs may be enhanced by planting shelter belts or nutrient trap crops where runoff is likely to occur.

How are CRFs or SRFs best used?

Crop nutrient requirements follow a dynamic pattern: they begin low in the early growth stage, increase sharply in the middle stage and decrease in the late stage (Figure 1). Conventional fertilizers (QRFs) are instantly available when they're applied, which makes them more vulnerable to loss from a variety of causes such as ammonia volatilization (ammonia emitting into the atmosphere), de-nitrification (nitrate is reduced to nitrogen), leaching, or runoff after being applied to the soil. Nitrogen and potash fertilizers are particularly easily lost. Assuming the same amount of fertilizer is applied, a one-time or seasonal application of conventional fertilizers has the potential to lose much more nitrogen than would be lost with multiple split-applications of fertilizer (Figure 2). Split applications of convention fertilizer are recommended (Hochmuth and Hanlon ).

Figure 1.

Credit: Guodong Liu, UF/IFAS

Figure 2.

Credit: Waskom, Cardon, and Crookston

To match crop nutrient requirements, the ideal fertilizer should have this characteristic: the nutrient release matches the nutrient requirements of the crop throughout all of the plant growth stages (Figure 3). Obviously, QRFs do not have this characteristic, and they cannot meet such requirements without repeat applications. Fortunately, using deliberate applications of CRFs and SRFs in specific circumstances where they are appropriate can accommodate timely plant nutrient demand requirements, maximize nutrient use efficiency, and minimize environmental concerns. There is a close relationship between CRFs and BMPs. Section 32 of Water Quality/Quantity Best Management Practices for Florida Vegetable and Agronomic Crops ( edition) discusses CRFs and BMPs including planning and application of CRFs.

Figure 3.

Credit: Adapted from Lammel

Take-Home Message

Quick-release fertilizers are water soluble and readily available for plants to take up when they are properly placed at the right time.
Controlled-release fertilizers contain a plant nutrient in a form that delays its availability for plant uptake and use after application, or that extends its availability to the plant significantly longer than "rapidly available fertilizers" such as ammonium nitrate or urea, ammonium phosphate, and potassium chloride.
Controlled-release fertilizers can dynamically release nutrients and meet the crop's changing nutrient demand throughout its growth cycle, maximize nutrient use efficiency, and minimize environmental concerns.
Slow-release fertilizers generally have a slower release rate of the nutrient than conventional water-soluble fertilizers and CRFs. However, the rate, pattern and duration of release are not well controlled because they are dependent on microbial activity that is driven by soil moisture and temperature conditions. Slow-release fertilizers can occasionally be released very quickly when excessive moisture and high temperatures occur in the same period.
Use of CRFs or SRFs can reduce nutrient losses, increase nutrient-use efficiency, and protect the environment. Thus, the application of CRFs or SRFs is a Best Management Practice (BMP) tool for crop production.

References

Clapp, J.P., Jr. . "Foliar application of liquid urea-triazone-based nitrogen fertilizers and crop safety." 3(4): 442'444.

Du, C., J. Zhou, A. Shaviv. . Release Characteristics of Nutrients from Polymer-coated Compound Controlled Release Fertilizers. Journal of Polymers and the Environment 14 (3): 223'230. https://link.springer.com/article/10./s-006--4

Gregorich, E. G., L. W. Turchenek, M. R. Carter, and D. A. Angers. . Soil and Environmental Science Dictionary. CRC Press. p. 132. ISBN 978-0---2. LCCN S592.S49 . Retrieved 30 December .

Lammel, J. . "Cost of the different options available to the farmers: Current situation and prospects." IFA International Workshop on Enhanced-Efficiency Fertilizers. Frankfurt. International Fertilizer Industry Association, Paris, France.

Liu, G., E. H. Simonne, K. T. Morgan, G. J. Hochmuth, S. Agehara, and R. Mylavarapu. . ' Vegetable Production Handbook: Chapter 2. Fertilizer Management for Vegetable Production in Florida. CV296. Gainesville: University of Florida Institute of Food and Agricultural Sciences. https://edis.ifas.ufl.edu/publication/CV296

Loper, S. and A. L. Shober. . Soils & Fertilizers for Master Gardeners: Glossary of Soil and Fertilizer Terms. SL 277. Gainesville: University of Florida Institute of Food and Agricultural Sciences. https://edis.ifas.ufl.edu/publication/MG457

Oertli, J. J. and J. Lunt. . "Controlled release of fertilizer minerals by encapsulating membranes: I. Factors influencing the rate of release." Soil Sci. Soc. Proc. 26: 579'583.

Robbins, J. "Slow-release fertilizers as tools." IFA International Workshop on Enhanced-Efficiency Fertilizers. Frankfurt, Germany, 28'39 June .

Ruark, M. . "Advantages and disadvantages of controlled-release fertilizers." https://soilsextension.webhosting.cals.wisc.edu/wp-content/uploads/sites/68//02/Overview_of_fertilizer_technologies__WIFFVC.pdf

Shaviv, A. . "Advances in controlled release of fertilizers." 71: 1'49.

Shukla, S., E. A. Hanlon, F. H. Jaber, P. J. Stoffella, T. A. Obreza, and M. Ozores-Hampton. . Groundwater Nitrogen: Behavior in Flatwoods and Gravel Soils Using Organic Amendments for Vegetable Production. CIR . Gainesville: University of Florida Institute of Food and Agricultural Sciences. https://edis.ifas.ufl.edu/publication/AE400

Trenkel, M. E. . "Slow- and Controlled-Release and Stabilized Fertilizers: An Option for Enhancing Nutrient Use Efficiency in Agriculture." International Fertilizer Industry Association (IFA) Paris, France.

Waskom, R. M., G. E. Cardon, and M. A. Crookston. . "Best Management Practices for Irrigated Agriculture." Colorado Water Resources Institute Report No. 184.

Wolf, B.. . The Fertile Triangle: The Interrelationship of Air, Water, and Nutrients in Maximizing Soil Productivity. Binghamton, NY: The Haworth Press, Inc.

Table 1.

Relative insoluble synthetic materials used as slow-release fertilizers.

Material

Trade name

P2O5

K2O

Guanylurea

G. sulfate

Magnesium ammonium phosphate

Mag-Amp

Oxalic acid diamide

Oxamide

31.8

Potassium calcium phosphate

KCP

17'22

21'22

Potassium poly-phosphate

KPP

29'32

24'25

Urea aldehyde

IBDU

CDU

Crotadur

Floranid

Glyyccluril

Ureaform

Agriform

4.8

Urea-Z

33'38

Dinauer, R. C. . Fertilizer Technology and Use. Soil Science Society of America, Inc., Madison, WI.

Hignett, T. P., E. Fredderick, and B. Halder (Eds.). . Fertilizer Manual. International Fertilizer Developemt Center. Muscle Shoals, AL.

Wolf, B. . The Fertile Triangle: The Interrelationship of Air, Water, and Nutrients in Maximizing Soil Productivity. The Haworth Press, Inc. Binghamton, NY.

View Table Table 2.

Relative insoluble synthetic materials used as controlled-release fertilizers.

Material

For more fertilizer water solubleinformation, please contact us. We will provide professional answers.

Trade name

P2O5

K2O

Resin coated

Osmocote

Sierrablen

Polyon

Procote

Nutricote

Woodlace

SCU

ESN

Agrocote

Dinauer, R. C. . Fertilizer Technology and Use. Soil Science Society of America, Inc., Madison, WI.

Hignett, T. P., E. Fredderick, and B. Halder (Eds.). . Fertilizer Manual. International Fertilizer Developemt Center. Muscle Shoals, AL.

Wolf, B. . The Fertile Triangle: The Interrelationship of Air, Water, and Nutrients in Maximizing Soil Productivity. The Haworth Press, Inc. Binghamton, NY.

View Table

What are Controlled Release Fertilizers?

Controlled Release Fertilizers (CRFs) are specialized fertilizers coated with a semipermeable membrane, designed to gradually release nutrients into the soil over time, providing a steady and predictable supply of essential nutrients to plants.These and other fFertilizers are used by farmers around the world to increase yields and produce better crops. They can supply a wide range of nutrients, from the three basic macronutrients (nitrogen, phosphorus, and potassium), to a number of micronutrients that assist with plant growth.

There are various types of fertilizers and different application methods (such as granular fertilizers, WSF or liquid, application before planting/seeding, broadcasting, top dressing, side dressing, through drip lines, or as a foliar feed) and one should consider the nutrient needs of your crop, the soil characteristics, and the time/resources available when deciding which fertilizer and application method to use.

With many farmers concerned with nutrient use efficiency and environmental impact, many have chosen to utilize controlled release fertilizers or CRFs. CRFs are granular fertilizers coated with a semipermeable membrane that gradually release nutrients into the soil over a given period of time and are commonly used across agricultural production.

Studies have shown that growers can achieve higher production and higher quality using CRFs while meeting new regulations to limit nitrogen losses to the environment.

CRFs are used in all agricultural and horticultural crops across the world and the specific CRF products differ for each crop, nutrient composition, release time, and more. Understanding how to use controlled release fertilizers, controlled release versus slow-release fertilizers, the advantages of controlled release fertilizers, and how ICL can help with all your CRF needs will help with CRF implementation in your practices.

History of CRFs

The first commercial plant fertilizer was patented in by Sir John Bennet Lawes and after 100+ years of research, the first Controlled Release Fertilizer (CRF) was created in by Archer Daniels Midland Company. Since then, world food production has become highly dependent on the use of fertilizers, as they help increase crop yields, enabling us to produce more food for more people. This increase in crop production in turn means that less land is needed for farming because of its efficient use.

However, there are some negative effects of fertilizers on the environment that have become deeply concerning. For example, the overapplication of fertilizers can result in excessive nitrogen running off of fields and into nearby bodies of water, disrupting the ecosystem.

By understanding how fertilizers work, specifically controlled release fertilizers, you can get an idea of how they play a key role in contributing to world food production and preserving the environment.

How do CRFs work?

Controlled Release Fertilizers (CRFs) are granular fertilizers that are covered by a semipermeable membrane and when applied to the soil, allow moisture to penetrate it and reach the nutrient(s) inside.

'The core of the controlled release fertilizers start to dissolve and day by day, at a rate influenced by soil temperature, small amounts of nutrients are released back into the rooting zone for plant uptake. This practice limits nutrient losses and offers predictable availability of nutrients (from 1-2 months, up to 16-18 months) that is aligned with the plant's needs,' explains Cristian Filote, ICL CRF's International Technical Manager.

CRFs are designed to provide farmers with maximum results with minimal effort. By regulating plant nutrient levels throughout the entire growth cycle, plants have limited exposure to nutrient deficiency and are able to have more uniform growth and usually higher yields.

Controlled Release Fertilizers vs. Slow Release Fertilizers?

It's important to know the difference between slow-release (SRF) and controlled-release fertilizers (CRF), as they serve different purposes and have different effects. While SRF and CRF are sometimes used synonymously (incorrectly), there are striking differences between controlled release versus slow-release fertilizers.

Slow release fertilizers (SRFs) involve a slower release rate of nutrients than conventional water-soluble fertilizers, but the rate, pattern, and duration of release are not controlled. This is because SRFs depend on microbial organisms, whose effectiveness is dependent on soil temperature and moisture conditions.

By comparison, controlled release fertilizers (CRFs) describe fertilizers that have a well-known and controllable rate, pattern and duration of release. CRFs are primarily granular fertilizers, soluble in water and the semipermeable barriers that are present on the outside of the granules to control the nutrient release.

The nutrient release of CRFs is steered by soil temperature. Depending on the region, soil temperature and CRF longevities can vary. The CRF Timer of ICL calculates and shows the nutrient availability from your CRF.

Advantages of CRFs

Along with understanding how to use controlled release fertilizers, there are numerous advantages of CRFs relating to environmental impact, improved nutrient use efficiency, increased or comparable yields, and reduced nutrient loss.

Limit Negative Environmental Impact

Nitrogen losses can occur in the field by leaching (when the soil becomes so saturated with water that the N isn't able to be absorbed), volatilization (the loss of applied nitrogen to the atmosphere as ammonia gas), and denitrification (when soil bacteria use nitrate for their respiration in the place of oxygen in the air and resulting in a net loss of nitrate from the soil system).
Latest lab trials, performed by specialized trial stations, demonstrate that ICL's CRFs can limit nitrogen losses by 54-61% from leaching, 32-54% by volatilization, and 11% by denitrification when compared to conventional urea.

Improve Nutrient Use Efficiency

Globally, nutrient use efficiency has been drastically low for the last 40 years, fluctuating between 40-50%, meaning that the majority of applied fertilizers are lost to the natural environment.
By targeting fertilizer application using CRFs, nutrient losses are reduced and higher nutrient use efficiency is achieved.

Provide Higher or Comparable Yields with Reduced Fertilizer Applications

ICL's Cristian Filote reported that several field trials with potato varieties and varying nitrogen applications in countries across Europe showed that CRFs (specifically Agromaster) can significantly improve the yield using the same amount of nitrogen applied as conventional fertilizers.
Additional studies conducted by ICL in Spain looking at rice production found that using CRFs increased the yield by 60% for each kg of nitrogen applied.
Farmers will also notice enhanced crop uniformity due to controlled nutrition from the controlled release fertilizers.

Reduce the Number of Applications and Save Resources

Limiting nutrient losses minimizes the risk of environmental harm and allows for fertilizer inputs to be used more effectively, therefore reducing the overall amount needed.
Reducing the number of applications needed saves farmers money by decreasing the labor and fuel needed overall and allowing them to profit more off of their harvest.

ICL's Role in CRFs

ICL's R&D team is continuously dedicated to developing new products and innovative technologies to improve the environmental profile of our plant nutrition and maintenance products and services. Starting with quality, raw materials, and high attention to detail, ICL creates reliable products that set the standard for controlled release fertilizers.

ICL's most recent fertilizer innovation, Agroblen with V-Factor, is a unique combination of CRFs with specific embedded organic growth enhancers. V-Factor is specifically designed to improve the root systems of young plants. Thanks to the fully coated N-P-K, and its application in planting holes (close to the root system), this product is the safest granular fertilizer that meets a plant's needs over a period of time.

Barbara Meijkamp, Sr. Scientist and Agronomist at ICL says, 'Innovating a poor product is easy, but improving a product that is already good and efficient, that is a challenge. Our team is always striving to further develop its products and create even better solutions for plants and [the] environment.' That's why ICL is a leading company in the global food, agriculture, and industrial markets.

Previous: None
Next: 5 Useful Properties of NPK-19:19:19

Comments