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AdvMatTechEnv: 2017: 1(1):38-47 ISSN: 2559 - 2637 38
FERTILIZERS WITH A DELAYED NUTRIENT RELEASE
Krzysztof LUBKOWSKI
West Pomeranian University of Technology, Faculty of Chemical Technology and Engineering, Department of Organic and Physical Chemistry,
42 Piastów Av., 71-065 Szczecin, Poland; ([email protected])
Abstract:
The paper presents the most important issues relating to the research and application of materials with controlled-release properties that can increase the effectiveness of nutrient uptake, alleviate the negative influence of fertilizers on the environment and reduce labor and energy consumption associated with the use of conventional fertilizers. The article discusses predominantly commercially available controlled-release fertilizers manufactured with the use of sulfur, thermoplastics, polyurethane and alkyd resins. The multistep diffusion model was pointed out as the best tool for the qualitative description and quantitative prediction of the nutrient release. Attention was also paid to the fertilizers prepared with the use of other materials like superabsorbents and polysulfone-based materials. Bio-composites of starch, lignin, cellulose and other natural or synthetic biopolymers were depicted as the most promising materials for the future application. The article contains also the quantitative analysis of bibliographic data and information on the market situation of fertilizers with a delayed nutrient release.
Keywords: Nutrient Use Efficiency; Controlled-Release Fertilizers; Release Mechanism
1. Introduction
Mineral fertilizers belong to the group of essential
products of agricultural industry. They provide
nutrients to crops, increase their growth and at the
same time they play an important role in regulating
both pH and fertility of the soil. Consumption of
mineral fertilizers grows with an increase of human
population and a need for increased food production
[1,2]. Human population doubled from 3,1 bln to
almost 6,2 bln between 1961 and 2001. At the same
time grain and meat production and fertilizer
consumption increased by the factor 1.4, 2.3 and
6.0, respectively [1]. Global population is expected
to reach 7.7, 8.1 and 9.6 bln in 2020, 2025 and
2050, respectively [3], therefore we should expect a
further increase in the production of mineral
fertilizers.
Consumption of mineral fertilizers has
systematically increased in recent years from 135 Mt
(81 Mt N, 32 Mt P2O5, 22 Mt K2O) in 2000/2001 to
185 Mt (112 Mt N, 41 Mt P2O5, 32 Mt K2O) in
2014/2015, with a slight decrease in consumption
occurring in 2008/2009 due to the crisis in the
banking system. Fertilizer consumption in the
2015/2016 season slightly dropped to 181 Mt, while
worldwide demand is forecast to reach 186 Mt and
199 Mt in 2016/2017 and 2020/2021, respectively
[4].
An increased production of fertilizers contrasts
with a relatively low nutrient use efficiency (NUE).
Assimilation of fertilizer nitrogen by plants is
approximately 50% on average [1,5-7], whereas an
uptake of phosphorous and potassium reaches 10-
25% and 50-60%, respectively [8-11]. Low
effectiveness of nutrients assimilation may cause
serious problems in view of environmental protection
[5,12-15] and human and animal health [1,5,14,16].
The economic aspect of the issue is no less
important [17,18]: annual losses of nutrients can be
estimated at 60-80 Mt, corresponding to the financial
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losses of 18-24 bln USD. During the production of 1
kg of fertilizer about 1 kg of oil is used [19], which
means irreversible lost of the natural resources. In
view of current and possible future energy problems
fertilizer losses must be minimized.
Developments in fertilizer production and
utilization that improved nutrient use efficiency have
been widely discussed and summarized elsewhere
[5,11,20,21]. An improvement in the effectiveness of
nutrients assimilation can be achieved, among others,
through development, production and application of
the so-called "intelligent fertilizers", which release
mineral components according to the nutrient
requirements of the plants [10]. The examples of such
materials are slow release fertilizers (SRF) and
controlled release fertilizers (CRF).
According to the specialists from the fertilizer
industry [22,23], fertilizer market in the world
(including even the stable European market) is going
to undergo significant changes in order to reduce
costs and maximize profits. Development and
application of SRF/CRFs might be a basis of these
processes. It is also expected [10], that due to the
restrictive law solutions, an influence of these type of
fertilizers on the agrochemical production and
natural environment will be systematically increasing
through the reduction of the amounts of leached
mineral components and through lowering of harmful
substances emission.
Slow- and controlled-release fertilizers are the
fertilizers produced in order to gradually release
mineral components, simultaneously ensuring the
proper plant nutrition [8-10]. According to the
Association of American Plant Food Control Officials
(AAPFCO) [24] slow-release fertilizers (SRF) are
chemically or biologically decomposed materials
with a high molecular weight, complex structure and
low solubility in water, whereas controlled-release
fertilizers (CRF) are materials in case of which the
release of mineral components takes place through
a polymer layer or a membrane.
Nutrients uptake by plants in their vegetation cycle
has a sigmoidal character [9,13,25]. An application of
SRF/CRF which release their nutrients in a way better
fitting plants’ requirements ensures an improved
effectiveness of fertilization through minimizing losses
between application and absorption [9]. At the same
time using SRF/CRF allows to reduce negative
influence fertilizers have on the environment largely
due to high solubility of nitrogen compounds which
are left unused [26,27]. In conventional fertilizing (e.g.
with urea) nutrients release lasts 30 – 60 days, which
given a 100 – 120 day long crops growth cycle means
that a fertilizers must be applied 2 or 3 times.
SRF/CRF release their nutrients slowly and gradually
during all vegetation season and consequently need
to be applied once only, which greatly reduces both
time and energy consumption. A better and more
efficient use of nutrients can lead both to a reduction
of waste material produced by the fertilizers industry
and to a reduction in natural gas and other resources
consumption [8-10,13]. Moreover, the ability of plants
to effectively utilize nutrients can be influenced by
other nutrients and micronutrients [9,28].
The objective of the paper is to present the
current state of knowledge in the field of the
fertilizers with a delayed nutrient release, however
the story will be especially focused on controlled-
release fertilizers, their preparation, properties,
nutrient release mechanism and market situation.
2. Slow-release fertilizers
Slow-release fertilizers are widely known from the
twenties of the 20th century [29,30], and they were
first time commercialized in the early fifties by the
Japanese company Mitsui Toatsu Chemicals. Slow-
release fertilizers comprises materials with complex
structure and little solubility in water like products of
urea and aldehydes condensation (urea-
formaldehyde products - UF, isobutylidene diurea -
IBDU, crotonylidene diurea - CDU, acetylene
diurea), various synthetic organic products with low
water-solubility (oxamides, guanylurea sulphate and
melamine), matrix-based formulations, with the
nutrients dispersed in the polymeric matrices
(natural rubber, styrene-butadiene rubber), inorganic
low-solubility compounds (metal ammonium
phosphates, metal potassium phosphates,
phosphate rocks, thermal phosphates, zeolites) and
polyphosphate-based micronutrient fertilizers. All
above-mentioned materials have been thoroughly
discussed in numerous papers and have been
recently reviewed in details [31].
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3. Controlled-release fertilizers
The first comprehensive and detailed studies on
the application of controlled-release technology to
fertilizers are to be dated on 1962 [32,33]. Most of
the available research papers concerns coated
fertilizers, i.e. the systems with the nutrients core
encapsulated with an inert substance. Part of the
accumulated knowledge was found to be of great
practical importance and has been successfully
commercialized. Technology of production of
controlled-release fertilizers consists in coating of
fertilizer granules with an inert layer or membrane
[19,32]. The first technology of this type - sulfur
coated urea (SCU) – was developed by TVA
company (Tennessee Valley Authority, USA) [34-36]
and a small continuous pilot plant was in operation
at TVA in the early seventies [37]. Urea granules are
pre-impregnated with small amounts of some
petrochemical waste products (e.g. technical
vaseline, engine oils) used to limit the penetration of
water into urea through slots in the sulfur coat. Then,
urea granules are coated with molten sulfur in a
drum granulator and then the material is "sealed"
with a small amount of wax (2-3 wt.%) and
conditioned with special inorganic substances to
prevent dusting and caking (2-3 wt.%). Presently
manufactured SCU fertilizers contain 30-42 wt.% of
nitrogen and 6-30 wt.% of sulfur. Sulfur coating
constitutes an impermeable membrane, which is
gradually degraded by microbial, physical and
chemical processes. The release of nitrogen varies
with the thickness of the coating layer and it
depends also on the quality and purity of used urea.
Sulfur is an excellent coating agent, because it is
relatively cheap and provides the soil with a valuable
secondary nutrient. Despite the undoubted
advantages, the release of nitrogen from SCU
fertilizers is relatively quick [10], hence their
importance is gradually decreasing in favour of the
polymer-coated fertilizers (PC – polymer-coated
fertilizers). In order to merge the beneficial
properties of polymer membranes with low-priced
sulfur coatings, the offer of controlled-release
fertilizers was enriched by the formulations in which
two coating layers were applied [38]. The sulfur layer
is the inner layer, whereas the polymer layer is the
outer one (PSCU – polymer/sulfur coated urea). This
type of encapsulation provides greater resistance to
abrasion, cracking and prevents adverse processes
during transport and storage of urea. Urea granules
are pre-heated in a fluidized bed and then coated
with sulfur and polyurethane by spraying in two
successive rotating drums. A modification of this
method has also been developed: urea granules are
covered with three layers - polyurethane-based
polymer, sulfur and again polyurethane [39],
resulting in a significant prolongation of the urea
release time. A very comprehensive and detailed
review on urea-based controlled-release fertilizers
(CRCU – controlled-release coated urea) has been
recently presented elsewhere [40]. This review
covers over fifty years research on urea
encapsulation and coating from the early sixties of
the 20th century up to the latest studies of the
present decade. The authors placed special
emphasis on the release experiments and release
mechanisms of CRCU prepared with the use of
sulfur, polymer, superabsorbent and bio-composites
based coating materials. Following the integrated
critical analyses of the referenced sources the
authors pointed out modified bio-composites of
starch, lignin and cellulose as the potential materials
that might fulfil the stringent and rigorous
requirements of future research.
Polymers are the second, after sulfur, most
popular material used for the controlled release of
fertilizers into the soil. Two types of organic polymer
coatings - resins and thermoplastics - were
thoroughly reviewed and characterized elsewhere
[13,41].
Resin coatings (alkyd resins and polyurethanes)
are prepared by in-situ polymerization with the
formation of a cross-linked, thermosettic and
hydrophobic polymer. The alkyd resins are
copolymers of diclopentadiene with a glycerol ester
and their prominent example is Osmocote®, the first
commercially manufactured resin-coated fertilizer
[42,43]. Polyurethane resins can be prepared in the
reaction of poly-isocyanates with polyols on the
surface of the fertilizer granule [44,45], with equally
distinct commercial representatives like Polyon®,
Plantacote® and Multicote®. Nutrient release from
resin-coated fertilizers can be controlled by the
coating composition and thickness.
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Thermoplastic coatings are prepared by
dissolving the coating material (e.g. polyethylene) in
a chlorinated organic solvent and spraying the
solution on the fertilizer granules in a fluidized bed
reactor [46-49]. Nutrient release from this type of
material can be controlled and regulated by varying
the ratio of the coating components with high and
low moisture permeability (e.g. polyethylene and
ethylene-vinyl-acetate for Nutricote®).
Compared with sulfur, polymer coatings are more
resistant to cracking and, putting aside biodegradable
materials, they do not undergo microbiological
degradation. The amount of coating material depends
on the granular geometry and the expected life time
of the product. As a rule, the coating material
represents up to 15% of the total weight of the
material, however with the Pursell RLC® (Reactive
Layer Coating) technology it is only 3-4%. The
thickness of the polymer layer is up to 1200 μm.
The mechanism of controlled release of nutrients
from CRF fertilizers is not fully explained. Mineral
components can be released from the fertilizer as a
result of diffusion, erosion, chemical reaction, swelling
or osmosis. The release mechanism depends on the
nature of the coating material, the type of fertilizer, the
agrotechnical conditions and the weather. It should be
kept in mind that the nutrient release from polymer-
coated fertilizer consists of several successive
processes: 1) transport of water from the soil solution
into the granule core, 2) dissolution of nutrients, 3)
backward transport of nutrient solution to the soil
solution and 4) propagation of nutrients in the soil
volume. Each stage affects the overall efficiency of
the release process, though it seems quite natural to
assume that the release is controlled either by the
rate of water diffusion or by the rate of the solute
diffusion [13].
Transport stages are primarily dependent on
temperature and the properties of the coating. When
the characteristics of the coating are known, it is
possible to accurately predict the release within a
given time interval. An influence of polymer layer
properties (e.g. porosity, thickness, water
permeability) as well as temperature and water
vapour pressure on the nutrient release has been
investigated in numerous papers, to cite only few [50-
55].
The nutrient release rate increases with the
solubility of fertilizer components [56], however in
the case of NPK-based controlled-release fertilizers
the picture seems to be more complex in
comparison with a single component fertilizer (e.g.
urea). It was reported in a series of papers
[13,48,57-59] that the release rate of phosphates is
lower than those of potassium, ammonium and
nitrates, however there was no consensus as to the
margin of that discrepancy. A conceptual model of
nutrient release from NPK-based controlled-release
fertilizers has been proposed [59] in which the
concentrations of the mineral components inside the
water-penetrated fertilizer granules and the diffusion
properties of the nutrients in water have been
indicated as the reasons for that discrepancy.
The dispersion of nutrients in the soil volume
follows the mechanisms of molecular diffusion and
mass transport and it depends also on temperature,
pH and humidity of the soil [53,56]. The release rate
was found to increase with temperature, whereas an
effect of soil moisture and pH changes was noted
but it was not pronounced.
While the above-mentioned qualitative
description of the nutrient release from CRF is
simple and understandable, the quantitative
representation of the issue in the form of a
mathematical kinetic model is significantly more
complicated. A detailed description and discussion
on the early developed kinetic models has been
presented elsewhere [13], hence below it will be
given only the brief outline of that issue.
In the first kinetic model developed for urea
release from sulphur-coated fertilizer [60,61] it was
assumed that water and urea diffuse through cracks,
pores and holes in the microbial-eroded coating.
Diffusion through the polymer layer was described
with the use of one-dimensional Fick’s first law of
diffusion. Consistent investigations led to the
development of other models, with Fick’s law applied
to spherical granules [62], with a first-order decay
process considerations [55,63] and with a quadric
equation used to predict the release of nitrogen [64].
Presented models covered the patterns of parabolic
and linear release, however they did not cope with
sigmoidal release, for they failed to describe the lag
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period (initial stage of sigmoidal release), observed
in the experiments [13].
Deficiency and imperfection of above-mentioned
approaches were overcome when developing two
other kinetic models. In the first one [52] the release
from a spherical particle of TVA sulfur-coated
fertilizer was calculated for the mass balance of
active agent (nutrient) with the use of Mechaelis-
Menten expression of decay law. As a result, an
excellent agreement was found between
experimental measurements and the data calculated
with the use of the kinetic model.
According to higly developed, multistep diffusion
model [65-68], after a fertilizer’s application water
penetrates through a hydrophobic membrane into
the inside of a granule. Then, nutrients are dissolved
and under the influence of the resulting osmotic
pressure, the granule swells and expansion of the
membrane takes place. When the osmotic pressure
exceeds the tensile strength of the membrane, the
coating cracks and the entire content of the core is
released immediately. This sequence is called
“failure mechanism” or “catastrophic release” [69].
When the membrane is resistant to rising osmotic
pressure, we are dealing with so-called “diffusion
mechanism", and mineral components are released
more slowly by diffusion-based ion transport through
the coating to the soil. Diffusion is driven by a
concentration gradient across the coating, or by
mass flow driven by a pressure gradient, or by a
combination of the two. The rate of nutrients’ release
is controlled by a diffusion coefficient of the coating.
The catastrophic release mechanism is observed for
brittle coatings (sulfur or modified sulfur) while in the
case of flexible polymeric coatings (e.g. polyolefins)
the diffusion mechanism should be expected.
The results obtained with the use of multistep
diffusion model were compared with experimental
results for the release from urea granules coated
with a polyurethane coating and from urea granules
coated with modified polyolefin giving also good
agreement between the calculated curves and the
experimental ones [68].
The multistep diffusion model was successfully
developed and adapted to predict the overall nutrient
release from NPK-based polymer coated fertilizers
[70-73] as well as the release of potassium [74,75]
and nitrates [76].
One of the drawbacks of controlled release
fertilizers, particularly polymer-coated CRFs, is that
after nutrient consumption, a considerable amount of
non-functional polymer remains in the soil, amounting
to approximately 50 kg/ha per year [10]. This obstacle
could be surmounted through the production of CRF
with the use of biodegradable materials [77], either
natural materials or biosynthetic materials
manufactured from renewable raw materials. Among
the various biodegradable materials used for this
purpose, however not having been implemented on a
large scale so far, starch and its derivatives seem to
be the most extensively investigated [78-82].
Cellulose and its derivatives [83-86], lignin [87-93],
chitosan [94-98] and polylactic acid [99-103] have
also been examined for this application recently, as
described in the literature.
Quite latterly a new, innovative, biodegradable
polymer - poly(butylene succinate-co-dilinoleate) –
has been proposed and successfully applied to
preparation of fertilizer materials with delayed nutrient
release [59]. Multicomponent fertilizer granules were
coated with a polymer layer using the immersion
method and as a result of the experiments the
product meeting the standard requirements of
controlled release fertilizers was obtained.
It seems absolutely reasonable to point out bio-
composites of starch, lignin, cellulose and other
natural or synthetic biopolymers as the potential
materials for the future manufacture of polymer-
coated controlled-release fertilizers. An application
of biodegradable polymers and their blends in the
preparation of controlled-release fertilizers has been
profoundly addressed in a very comprehensive
review [104].
Research on the controlled-release fertilizers was
also focused on other, various materials. For example
several papers were dedicated to the application of
polysulfone, which together with additives (cellulose
acetate and polyacrylonitrile) was used to coat the
fertilizer granules [105-109]. The polymer coatings
were formed on the granular NPK fertilizer from
polymer solutions by a phase inversion technique or
spraying method. As the polysulfone coatings are not
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biodegradable, starch was added to facilitate
destruction of polymer coatings in soil. Prepared
materials proved to have good controlled-release
properties and high bioavailability of the
micronutrients, however they seem to be of no
agroeconomic importance at the moment.
Another group of materials that were extensively
investigated for their possible use in controlled-
release fertilizers manufacture are synthetic
hydrophilic polymers derived from vinyl and acrylic
monomers, including the most important cross-
linked polyacrylamide, hydroxyethyl methacrylate
and polyvinyl alcohol [110]. Hydrophilic polymers,
known also as superabsorbents, are three-
dimensional structures capable of swelling and
retaining huge volumes of water in the swollen state.
The agricultural applications of thus obtained
“hydrogels” consist in improving water retention in
soils and controlled release of agrochemicals. The
release of nutrients from hydrogel-based controlled-
release fertilizers can be delayed when compared
with the conventional fertilizer. Thus, the prepared
product could effectively improve the utilization of
fertilizer and water resource at the same time. The
synthesis conditions of polymerization, swelling rate,
nutrient release, and water retention properties of
the multicomponent controlled-release fertilizers
prepared with the use of differently modified
superabsorbents have been reported in numerous
papers [111-122]. Despite the commercial
usefulness of this type of fertilizers is quite
promising, they are also of no agroeconomic
importance at the moment. Nonetheless, they
remain very interesting and attractive from the
scientific point of view.
Fig. 1. Publications related to SRF/CRF depending on the language of the publication:
the total amount in the years 1960-2016 (up), the amount in the individual decades (down)
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4. Quantitative analysis of bibliographic data
Based on the bibliographic data contained in the
Chemical Abstracts Database (SciFinder Platform)
[123], it has been found (Fig. 1) that approximately
9978 publications related to slow- and controlled-
release fertilizers were published in the years 1960-
2016, whereof 5852 (58.6%) were written in
Chinese, 2525 (25.3%) in English, 755 (7.6%) in
Japanese, 229 (2.3%) in Russian, 155 (1.6%) in
German and the rest 462 (4.6%) in other languages.
However, taking into account the number of
publications in different decades, it is clearly seen
that most of the publications in Chinese (5779) has
been released in 2000-2016. However, excluding
the publications in Chinese, it turns out that the
increase in the number of publications in different
decades is linear. On this basis it is possible to
estimate and predict the number of publications that
will be issued by the end of 2020 to about 1700. In
order to complete the picture, it is worth mentioning
that the total amount of publications on SRF/CRF
from the period 2000-2016 (8008) represents merely
5.9% of all publications related to fertilizers in
general. Signaled tendencies are even more
noticeable when analyzing the quantity of patents
relating to SRF/CRF (Fig. 2). 6662 patents were
granted in the years 1960-2016, of which 4921
(73.9%) are patents published in Chinese, although
only 43 of them were registered before 2000.
Fig. 2. Patents related to SRF/CRF depending on the language of the publication:
the total amount in the years 1960-2016 (up), the amount in each decades (down)
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Fig. 3 shows on the other hand data on the
amount of publications on SRF/CRF, but not
involving patents. 3316 scientific articles have been
published in various journals in the years 1960-
2016, of which 1952 (58.9%) were published in
English, and 931 (28.1%) in Chinese, however again
the majority of Chinese publications (901) was
released in the years 2000-2016. Publications in the
Japanese, German, Russian and other languages
account only for 13% of all publications.
Fig. 3. Publications related to SRF/CRF (not involving patents) depending on the language of the publication:
the total amount in the years 1960-2016 (up), the amount in each decades (down)
The number of publications related to SRF/CRF
issued in 2000-2016 are shown in Fig. 4. The total
number of publications and the number of patents
have increased significantly since 2005, however the
increase in the number of publications in English is
negligible: if not for 2012 (118 publications), their
quantity would be maintained at 70-80 per year. The
intense increase in the volume of publications over
the considered period is due to the increased activity
of Chinese researchers (Fig. 5), which correlates
well with data on the production of SRF/CRF
fertilizers on the Chinese market (see point 5).
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Fig. 4. Publications related to SRF/CRF issued in the years 2000-2016: in all languages (up), in English (down).
5. Market situation
Despite many advantages of slow- and
controlled-release fertilizers and the fact that they
have been constantly developed, their use is still
very limited. This is due to their high prices; SCU,
UF and PC fertilizers are 2, 35 and 48 times more
expensive than commonly used fertilizers [10].
The world production of SRF/CRF and their
consumption on the three traditional markets
(American, European and Japan) amounts to
approximately 1.4 Mt [124], and it constitutes merely
0,5% of the total fertilizer production. This production
is generated by about 30 manufacturers [124]. The
most important and leading suppliers of
manufactured slow- and controlled-release fertilizers
are listed in Table 1. The U.S. SRF/CRF market
amounts to approximately 0.7 Mt and it is almost five
times larger than the Western European market and
nearly 13 times larger than the Japanese market
[125]. Urea reaction products account for most
CRFs consumption in Western Europe, whereas
coated fertilizers predominate in Japan and the
United States [125]. SRF/CRF are predominantly
used in nonfarm markets like golf courses and other
professional turf, consumer lawn and garden
fertilizers, professional lawn care and landscape
maintenance, professional horticulture, and
landscapers [124]. About 10% is used for high-value
specialty agricultural crops (e.g., strawberries, citrus,
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vegetables) and also for major agricultural crops
such as corn, wheat, cotton, rice, and potatoes
[125]. The exception is Japan, where 90% is
consumed in rice production [23]. Consumption of
SRF/CRF by the type of fertilizer is as follows: UF -
40%, PC - 24%, SCU + PSCU - 19%, IBDU/CDU -
15%, others - 2% [10]. According to the experts’
opinion [126], world agricultural crop markets for
slow- and controlled-release fertilizers are ready for
very strong growth and total world consumption of
coated fertilizers will continue to grow at a
significantly faster rate than consumption of urea
reaction products. Taking into account the current
pace of fertilizer industry development (2% -
conventional fertilizers, 4-5% - SRF/CRF), the
production of SRF/CRF in 2020 may amount to
around 2.1-2.3 Mt.
In the last decade, the production and
consumption of SRF/CRF fertilizers has significantly
increased on the rapidly growing Chinese market.
The number of companies producing this type of
fertilizers is not well known, nonetheless estimates
show 70 to 200 business entities [126]. The largest
Chinese suppliers of SRF/CRF are Shikefeng
Chemical Industry (SCU and SC-NPK), Shandong
Kingenta Ecological Engineering (SCU, PCSCU and
PCF), Hanfeng Evergreen (SCU, PCU, SC-NPK),
Summit Fertilizer (UF-based compound fertilizers),
Wuhan Lvyin Chemical (urea-form, MU, UF
solutions, IBDU) and Shanghai Huaxuan Chemical
(urea-form, MU, UF solutions) [126]. The volume of
Chinese production in 2005, 2010 and 2015 was
assessed at 1.4 Mt, 7 Mt and 10 Mt, respectively
[126], which means that it is currently about 10 times
larger than the rest of the world.
The Chinese market for slow- and controlled-
release fertilizers is growing very strongly. Intensive
research into the use of SRF/CRF for agricultural
crops is expected to stimulate continuing market
growth. China is the world’s largest consumer of
fertilizers and the potential market for SRF/CRF in
this country is enormous [126]. Extremely rapid
development of SRF/CRF technology on the
Chinese market is also reflected in the number of
publications related to that issue and it was
emphasized and analyzed in the previous paragraph
of the paper.
Fig. 5. Publications related to SRF/CRF issued in the period 2000-2016, depending on the language of publication.
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Table 1. Leading suppliers of manufactured slow- and controlled-release fertilizers.
Company CRF SRF
AGLUKON, Germany
Plantacote® – polyurethane-coated NPK fertilizers
Plantodur®, Plantosan®, Azolon® – methylene urea (MU)
AGRIUM, USA ESN® Smart Nitrogen – polymer-coated urea
-
THE ANDERSONS, USA
Poly-S®, NS-54® – polymer-coated sulfur-coated urea (PCSC) Extend® – polyurethane-coated urea
MUtech® – methylene urea (MU) LN3® – urea-triazone technology
CENTRAL GLASS, Japan
Cera-Coat® – NPK coated with a vegetable oil-based polyurethane resin
COMPO, Germany Basacote® – polymer wax-coated NPK fertilizers
Isodur® - IBDU
GEORGIA-PACIFIC CHEMICALS, USA
INSOL-U-25®, STA-FORM60® – urea-formaldehyde concentrates (UFC)
GROWTH PRODUCTS, USA
Nitro-30 SRN – methylene urea (MU)
HAIFA CHEMICALS, Israel
Multicote® – polymer-coated NPK fertilizer CoteN® – polymer-coated urea
HELENA CHEMICAL
COMPANY, USA
CoRoN® – polymethylene-urea coupled with fast-release, low-biuret urea
ICL, USA Osmocote®, Ficote® – NPK coated with diclopentadiene-based resins
Osmoform®
JCAM AGRI, Japan Meister® – polyolefine-coated urea Nutricote® – polyolefine-coated NPK
IBDU
KNOX FERT, USA SurfCote® - polymer resin-coated NPK
KOCH Turf&Ornamental,
USA
Polyon® – polyurethane-coated urea and NPK fertilizers Duration CR® – polymer-coated urea XCU® – urea with two layers: the outer of sulfur and polymer wax and the inner of cross-linked polymer film
Nutralene® – methylene urea (MU) Nitroform® – urea-formaldehyde (UF)
KUGLER, USA Kugler KQ-XRN®
LEBANON SEABOARD, USA
Poly-X® – polymer-coated sulfur coated urea
Par-Ex® – IBDU
LESCO, USA Poly-Plus® – polymer-coated sulfur coated urea
Novex® – amino-ureaformaldehyde
MORRAL, USA NBN-30® – urea-triazone
PUCCIONI, Italy Smartfert® – NPK with urea-formaldehyde N-Force® - urea-formaldehyde
TESSENDERLO KERLEY, USA
TRISERT® – urea-triazone
6. Conclusions
Controlled-release fertilizers are numerous and
diverse group of materials that can improve the
effectiveness of fertilization, mitigate the negative
impact of fertilizers on the environment and
reduce labour and energy consumption connected
with the application of conventional fertilizers.
Krzysztof Lubkowski
Fertilizers with a delayed nutrient release
AdvMatTechEnv: 2017: 1(1):38-47 ISSN: 2559-2637 42
Controlled-release fertilizers of commercial
importance comprise the following materials:
sulfur-coated urea, polymer/sulfur-coated urea,
polymer-coated multicomponent fertilizers with
alkyd-type resin, polyurethane resin and
thermoplastic coatings.
Making use of the SRF/CRF market
potential, their development, production and
application requires the elaboration of a few
important issues. First of all there is a demand for
the manufacture of materials with lower prices
compared with the commonly used SRF/CRF,
with the special focus on the possibility of
biodegradable materials application. Attention
should be paid to appropriate controlling of the
fertilizers properties and better understanding of
the nutrient release mechanism and development
of the nutrient release kinetics. Development of
new methods of controlled release examination
and preliminary assessment of the obtained
fertilizers influence on the environment should not
be also neglected.
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