FERTILIZERS WITH A DELAYED NUTRIENT RELEASEsciedtech.eu/AdvMatTechEnv/Vol 1/Issue 1/AMTE_2017_1_1_Lubkowski.pdf · fertilizers with a delayed nutrient release, however the story will

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

mailto:[email protected]

Krzysztof Lubkowski

Fertilizers with a delayed nutrient release

AdvMatTechEnv: 2017: 1(1):38-47 ISSN: 2559-2637 39

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].

Krzysztof Lubkowski



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.

Krzysztof Lubkowski



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

Krzysztof Lubkowski



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

Krzysztof Lubkowski



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)

Krzysztof Lubkowski



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)

Krzysztof Lubkowski



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).

Krzysztof Lubkowski



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,

Krzysztof Lubkowski



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.

Krzysztof Lubkowski



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



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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