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The diffusion performance of fertilizer nutrient through polymer latex film Di An, Ling Yang, Boyang Liu, Ting-Jie Wang, and Chengyou Kan J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.7b04225 • Publication Date (Web): 27 Nov 2017 Downloaded from http://pubs.acs.org on November 27, 2017

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Journal of Agricultural and Food Chemistry

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The diffusion performance of fertilizer nutrient through polymer

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latex film

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Di An, Ling Yang, Boyang Liu, Ting-Jie Wang* and Chengyou Kan

5

Department of Chemical Engineering, Tsinghua University, Beijing 100084, China

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*Corresponding author: Phone: +86-10-62788993. Fax: +86-10-62772051. Email:

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[email protected]

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Abstract: Matching the nutrient release rate of coated fertilizer with the nutrient uptake rate of the

10

crop is the best way to increase the utilization efficiency of nutrient and reduce environmental

11

pollution from the fertilizer. The diffusion property and mechanism of nutrients through the film is

12

the theoretical basis for the product pattern design of coated fertilizer. For the coated fertilizer with

13

single-component nutrient, an extended solution-diffusion model was used to describe the

14

difference of nutrient release rate, and the release rate is proportional to the permeation coefficient

15

and the solubility of nutrient. For the double and triple component fertilizer of N-K, N-P and

16

N-P-K, because of the interaction among nutrient molecules and ions, the release rates of different

17

nutrients was significantly affected by the component in the composite fertilizer. Coating the

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single-component fertilizer, i.e., nitrogen fertilizer, phosphate fertilizer and potash fertilizer firstly,

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and subsequently bulk blending is expected to be the promising way for flexible adjusting the

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nutrient release rate to meet the nutrient uptake rate of the crop.

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Key words: Coated fertilizer, Polymer latex, Nutrient, Controlled release, Diffusion

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ACS Paragon Plus Environment


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1. Introduction

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Fertilizing control-release fertilizer with film coated is a promising way to increase the

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utilization efficiency of nutrient and reduce environmental pollution from the fertilizer1, 2. The

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nutrient release process of film coated fertilizer consists of three stages3, 4: (1) Water vapors

27

permeate through the film into interior of the coated fertilizer, and dissolve part of the fertilizer to

28

form a saturated nutrient solution in the interior. The vapor pressure gradient across the film is the

29

driving force in this stage. (2) The nutrient starts to release by the driving force of the

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concentration gradient across the film. While the water constantly diffuses into the film to dissolve

31

the fertilizer core at the same time, and the concentration of the internal solution remains saturated.

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(3) After the fertilizer in the core is dissolved completely, the concentration of the solution

33

decreases as the release proceeds, and the release rate decreases accordingly. In the three stages,

34

the second stage is the main stage of nutrient release from the film-coated fertilizer. Ideally,

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matching the nutrient release rate with the nutrient uptake rate of the crop can decrease the

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nutrient concentration in the soil, which reduce the loss of nutrient to water, volatilization to air

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and the mineralization in soil, achieving the efficient use of fertilizer3.

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For the coated fertilizer with the same film coating, the release rate of different nutrient is

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quite different. Huett et al.5 measured the release performance of coated compound fertilizer

40

formulations of Osmocote (A brand of coated fertilizer produced by The Scotts Company, USA),

41

and reported that the release rate was in the order of N > K > P. Broschat et al.6 measured the

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release performance of polyolefin coated fertilizer with the nutrient content of being 13% of N, 13%

43

of P2O5 and 13% of K2O. The release rate obtained was in the order of NO3- > NH4+ > K+ > P. Lu

44

et al.7 measured the release property of thermosetting resin coated fertilizer, and the release rate


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was in the order of K > N > P, the slowest release rate of phosphorus is explained by its slowest

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dissolution rate. Du et al.8 measured the release performance of polyurethane coated fertilizer with

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the nutrient content being 19% of N, 6% of P2O5 and 13% of K2O and reported that the release

48

rate was in the order of NO3- > NH4+ >K > P, and the delay time of the phosphorus release is much

49

longer. It was explained that the higher solubility of nitrogen and potassium resulted in their faster

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release rate, and until most of the nitrogen and potassium release, phosphorus began to dissolve

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and release. The different solubility of the nutrients is considered to cause the difference in

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nutrient release rate5-8.

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Besides the solubility of nutrients, the interaction between nutrients and the film also affects

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the nutrient release rate. Noppakundilograt et al.9 prepared coated fertilizer with acrylic

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acid-acrylamide copolymer, and measured the release rate being in the order of NH4+ > P > K+.

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Although the NH4+ and K+ have almost the same mobility in water and the same positive charge

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value, the size of K+ is smaller than that of NH4+. So the K+ has a higher surface area charge

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density to interact with the negatively charged carboxyl of the acrylic acid-acrylamide copolymer,

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resulting in that the release rate of K+ is lower than that of NH4+.

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The amount and rate of the crop’s demand for nitrogen, phosphorus and potassium nutrients

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are different, and it is desired for the release of nutrients in the coated fertilizer to match the crop’s

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demand. Presently, although there are some relevant studies on the release property of different

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nutrient in coated fertilizer, these studies lacked quantitative, systematic and in-depth analysis.

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The polymer latex, of which the continuous phase is water, is free from toxic organic solvents, so

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it is an environmentally benign and promising material for producing film coated fertilizer10. The

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study of the diffusion property and mechanism of different nutrient through the film, especially the



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polymer latex film, can provide a theoretical basis for the product and production process design

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of coated fertilizer, which is of great significance to achieve the precise release of the fertilizer.

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In this work, the planar film was prepared using styrene-butyl acrylate-methyl methacrylate

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copolymer latex. The diffusion performance of different kinds of nutrient in different fertilizer

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across the polymer latex film was measured and the diffusion mechanism was analyzed.

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2. Experimental

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2.1 Materials

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The chemical regents used include urea, NH4Cl, (NH4)2SO4, NH4H2PO4, (NH4)2HPO4, KCl,

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K2SO4, KNO3 (Beijing Chemical Works, China), ethanol, p-dimethylaminobenzaldehyde,

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ammonium metavanadate, ammonium molybdate (Sinopharm Chemical Reagent Co., Ltd, China),

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which are all analytical reagent grade. The copolymer latex of styrene-butyl acrylate-methyl

79

methacrylate with 40% solid content was used to prepare the planar polymer film. The latex was

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synthesized via a semicontinuous emulsion copolymerization in the Department of Chemical

81

Engineering, Tsinghua University. The water used in the experiment was ultrapure water, its

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resistivity was 18 MΩ·cm.

83 84

2.2 Film preparation

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A 250 mm×250 mm rectangular area of a glass sheet was surrounded by medical tape with a

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thickness of 80 µm. 8 g of polymer latex was diluted to 10 g with ultrapure water and then the

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diluted latex was dropped onto the center of the rectangular area to produce a film by scraping

88

with a glass rod. The glass sheet with latex coating was put in an oven at 120 oC for 1 h to remove


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the water in the latex and increase polymer cross-linking in the film. The formed film with

90

uniform thickness was then cooled to room temperature and taken down from the glass sheet for

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subsequent permeability measurement.

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2.3 Preparation of the saturated nutrient solutions

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In order to measure the diffusion performance of different nutrients in single-component

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fertilizer through the film, the saturated solutions of urea ((NH2)2CO), NH4Cl, (NH4)2SO4,

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NH4H2PO4, (NH4)2HPO4, KCl, K2SO4 and KNO3 at 25 oC were prepared respectively.

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In the measurement of the diffusion coefficient of the nutrients in double-component

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fertilizer through the film, i.e. N-P and N-K composite fertilizer, the saturated solutions of

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urea-KCl and urea-NH4H2PO4 at 25 oC were prepared respectively according to the composition of

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the commercial fertilizer products. The saturated solutions for the double and triple components

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indicates that all of the components exist in both solid and liquid phase. In the preparation process,

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it is necessary to ensure that each component is saturated in the solution, that is, the quality of

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each component added exceeds the corresponding solubility when it exists alone in the solution.

104 105 106

The phase rule of multicomponent salt-water solutions under isothermal and isobaric conditions is expressed as11: F = C − Ph

(1)

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where F is the freedom degree of each component concentration in the system, C is the number of

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independent components, and Ph is the number of coexisting phase in the system. For urea-KCl

109

saturated system, C=3, and the system contains urea solid phase, KCl solid phase and liquid phase,

110

so Ph=3. From Eq. (1), the freedom degree of the system, F=0. That is to say, the concentration of



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each component in the saturated solution is a fixed value and does not change with the amount of

112

solid component added. The urea-NH4H2PO4 saturated solution has the similar case, and the

113

freedom degree of the system, F=0.

114

In the measurement of the diffusion performance for the nutrients in triple-component

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fertilizer, i.e. N-P-K composite fertilizer, the saturated solution of NH4Cl-ammonium

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phosphate-potassium salt was prepared according to the composite of the commercial fertilizer

117

products. Specifically, four groups of composite saturated solution, i.e., NH4Cl-NH4H2PO4-KCl,

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NH4Cl-(NH4)2HPO4-KCl, NH4Cl-NH4H2PO4-K2SO4, NH4Cl-(NH4)2HPO4-K2SO4 at 25 oC were

119

prepared respectively, and in the preparation process, each excessive solid component comparing

120

to

121

NH4Cl-(NH4)2HPO4-KCl, C=4, and the systems contain three solid phases and one liquid phase,

122

i.e., Ph=4, so F=0, the concentration of each component is a fixed value. However, for the

123

saturated solutions of NH4Cl-NH4H2PO4-K2SO4 and NH4Cl-(NH4)2HPO4-K2SO4, C=5, and Ph=5,

124

so F=0, the concentration of each component is also a fixed value. Considering the most widely

125

used nutrient ratio of N:P2O5:K2O=1:1:1, which is the most representative, its saturated solution

126

was prepared as shown in Table 1.

water

was ensured. For

the saturated solutions of NH4Cl-NH4H2PO4-KCl and

127

Table 1. Amount of component in NH4Cl-NH4H2PO4-K2SO4 and NH4Cl-(NH4)2HPO4-K2SO4

128

systems (N:P2O5:K2O=1:1:1) NH4Cl-NH4H2PO4-K2SO4 (g)

NH4Cl-(NH4)2HPO4-K2SO4 (g)

NH4Cl

NH4H2PO4

K2SO4

water

NH4Cl

(NH4)2HPO4

K2SO4

water

165.6

87.7

100

200

187.5

150

150

200

129 130

2.4 Measurement of ﬁlm permeability


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The main stage of nutrient release of the film coated fertilizers is the release of saturated

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nutrient solution from the interior of the film to the external water environment. So in order to

133

simulate the release process, a Ussing chamber12 was used to measure the diffusion performance

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of nutrient through the polymer latex film, as shown in Figure 1. Both sides of the Ussing chamber

135

have a volume of 100 mL and the connection neck has an inner diameter of 30 mm. The film was

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cut into a circular shape with a diameter of 40 mm and its thickness was measured. Then the film

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was fixed in the middle of Ussing chamber, clamped with a clip and sealed with waterproof glue.

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The saturated nutrient solution was added to the supply side, and the ultrapure water was added to

139

the receiving side. Both sides were kept at the same height at the beginning. The Ussing chamber

140

was sealed on top and placed into an incubator at 25 oC. After a set time, the mass of nutrient

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diffusing into the receiving side was measured.

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For single-component fertilizer, the concentration of urea was measured by UV-Vis

143

spectrophotometric method using p-dimethylaminobenzaldehyde as chromogenic agent13, the

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concentration of NH4Cl, (NH4)2SO4, KCl, K2SO4, KNO3 was determined by measuring the

145

conductivity of the solution in the receiving side. The concentrations of NH4H2PO4 and

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(NH4)2HPO4 were measured by ion chromatography14. For double and triple component fertilizer,

147

the concentrations of NH4+, K+ and H2PO4- / HPO42- in the solution of the receiving side were

148

measured by ion chromatography.

149 150

3. Results and discussion

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3.1 Diffusion property of single-component fertilizer solution

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The change of different nutrient mass diffused to the receiving side with time is shown in



153

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Figure 2.

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Figure 2 shows that the diffusion process of the nutrient through the film has two stages. In

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the first stage, the nutrient permeates through the film, and the mass of nutrient in the receiving

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side was almost zero. In the second stage, the diffusion went to the steady, and the mass of nutrient

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entering into the receiving side increased linearly with time, indicating that the diffusion flux of

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the nutrient is constant. As the concentration of the nutrient in the receiving side is much lower

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than that in the supply side, the concentration difference between both sides is regarded as the

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concentration in the film phase in the supply side, i.e., Cm0, is a constant. Therefore, the nutrient

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diffusions through the film are consistent with Fick’s law, as shown in Eq. (2).

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J = D⋅

dCm C = D ⋅ m0 dL L

(2)

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where J is the diffusion flux, D is the diffusion coefficient of nutrient in the film, dCm/dL is the

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concentration gradient of nutrient in the film phase, L is the thickness of the film.

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The nutrient diffusion can be described by the solution-diffusion model15, 16. The permeation

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of nutrients in the model has three steps: (1) the partition of nutrients into the film phase in the

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supply side; (2) the diffusion of nutrients through the film; (3) the partition of nutrients into the

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solution phase in the receiving side. Step (1) and (3) are fast steps, and step (2) is the limiting step.

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Meantime, in the steady stage of diffusion, the diffusion flux of nutrients in the steady stage can

170

also be expressed as,

171

J = Pe ⋅

Cl 0 C = Pe ⋅ s L L

(3)

172

where Pe is the permeation coefficient of nutrient across the film, Cl0 is the concentration in the

173

solution phase in the supply side, which is the saturated concentration in the solution, Cs. The

174

partition coefficient between the film and solution phase, i.e., K is expressed as follows,


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175

176

181 182

183

K =Pe /D

(5)

where Pe can be calculated according to Eq. (3), and D can be calculated by time-lag method17,

179 180

(4)

From Eq. (2) - Eq. (4), there is,

177 178

Cm 0 Cl 0

K=

D=

L2 6θ

(6)

where θ is the time it takes for nutrient to reach the steady diffusion stage. The parameters of diffusion performance for each nutrient were calculated and reported in Table 2. Table 2. Parameters of diffusion performance for each nutrient through the film Nutrients

L(µm)

θ(h)

D(10-13 m2/s)

Pe(10-17 m2/s)

K(10-3)

urea

50

1.40

0.83

51.9

6.3

KCl

50

0.62

1.86

25.1

1.3

KNO3

52

1.00

1.25

23.2

1.9

K2SO4

70

1.90

1.19

79.9

6.7

NH4Cl

60

1.34

1.24

8.26

0.67

(NH4)2SO4

72.5

2.46

0.99

8.70

0.88

(NH4)2HPO4

55

4.33

0.32

0.25

0.08

NH4H2PO4

60

12.5

0.13

0.22

0.16

184

Table 2 shows the diffusion performance for different nutrient through the film. For nutrients

185

with the same cation K+, the measured D was in the order of KCl > KNO3 > K2SO4. For nutrients

186

with the same cation NH4+, the measured D was in the order of NH4Cl > (NH4)2SO4 >

187

(NH4)2HPO4 > NH4H2PO4. For nutrients with the same anion, the D of potassium salt is higher

188

than that of ammonium salt. This can be explained by extended solution-diffusion model16, 18.

189

Based on free volume model of polymer19, the volume of the polymer consists of two parts: one is

190

the volume of the molecular chain itself, the other is the free volume, that is, the volume among

191

the molecular chains. The extended solution-diffusion model approximates the free volume with



Page 10 of 22

192

hypothetical cylindrical capillary pores having a mean average pore radius, and the D can be

193

related to the diffusion coefficient of nutrient in infinite water Dw∞ by hindrance factor H(λ),

194

which can be expressed as follows,

D = H (λ ) ⋅ Dw∞

195

(7)

196

where λ is the ratio of the nutrient radius rs to the capillary pore radius r0, that is λ = rs r0 . H(λ)

197

represents the diffusion resistance of nutrients in the polymer film, it is negatively correlated with

198

λ. The Dw∞ of urea was reported to be 1.389×10-9 m2/s20, and the Dw∞ of electrolyte nutrient can

199

be calculated by the limiting molar conductivity in water of its dissociated ions, the formulas were

200

shown as follows21,

201

D ∞j =

202

Dw∞ =

RT λ j

(8)

Z j Fa 2

( Zi + Z j ) Di∞ D ∞j

(9)

Zi Di∞ + Z j D ∞j

203

where D ∞j is the diffusion coefficient of ion in infinite water, λ j is the limiting molar

204

conductivity of ion in water, Z j is the charge value of ion, R is the ideal gas constant, Fa is the

205

Faraday constant, T is the temperature of the solution. The Dw∞ of each nutrient at 25 oC was

206

calculated and reported in Table 3. The radius of each nutrient molecule and ion was reported in

207

Table 4

22-24

. Table 3. Diffusion coefficient of nutrient in infinite water

208

Nutrients

Dw∞ (10-10 m2/s)

Nutrients

Dw∞ (10-10 m2/s)

urea

13.89

NH4Cl

20.05

KCl

19.94

(NH4)2SO4

15.43

KNO3

19.29

(NH4)2HPO4

12.64

K2SO4

15.35

NH4H2PO4

11.85

209


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Table 4 Radius of each nutrient molecule and ion

210

Nutrients urea +

K

NH4 -

Cl

Nutrients

Radius(Å) 1.80

1.89

2-

2.15

NO3

1.38 +

SO4

1.61

HPO4

1.81

Radius(Å)

-

2-

2.30

-

2.38

H2PO4

211

Based on the parameters of each nutrient reported in Table 3 and Table 4, the regularity of D

212

of different nutrient can be explained. For nutrients with the same cation, as the radius of anion rs

213

increases, the H(λ) of nutrient decreases correspondingly, and the Dw∞ of nutrient also decreases.

214

According to Eq. (7), the D decreases as radius of anion increases. For nutrients with the same

215

anion, the difference of Dw∞ between potassium salt and ammonium salt can be neglected, while

216

the radius of NH4+ is larger than that of K+, so the H(λ) of ammonium salt is lower, and the D of

217

ammonium salt is lower. It is shown that the larger the size of the nutrient molecules and ions are,

218

the lower the diffusion coefficient of them in the film.

219

The results showed that the K of each nutrient is much lower than 1, which means the

220

concentration of nutrient in film phase is much lower than that in solution phase. Among the

221

nutrients, the K of urea and potassium salt are relatively higher, indicating that they have relatively

222

higher solubility in the film. According to Eq. (5), the differences of D and K among different

223

nutrients make the Pe of nutrients vary a lot. The permeation coefficient across the film, Pe, is

224

determined by the partition coefficients between the film phase and the solution phase, and the

225

diffusion coefficient of nutrients in the film.

226 227 228

For the coated fertilizer with single-component nutrient, the release rate, i.e., the mass of nutrient released from coated fertilizer granular per unit time, can be expressed as follows: dm Pe ⋅ ∆C ⋅ S = dt L


(10)


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where m is the mass of nutrient released, dm/dt is the release rate of coated fertilizer granular. ∆C

230

is the concentration difference between the inside and the outside of the coated film. In the steady

231

stage of nutrient release process, the concentration of nutrient solution inside the coated film is the

232

saturated concentration Cs, which is much higher than that in the external water environment, so

233

∆C=Cs, S is the mass transfer area, for the spherical coated fertilizer granular with a radius of R,

234

S=4πR2, L is the thickness of the coated film. So Eq. (10) can be re-expressed as follows:

dm Pe ⋅ Cs ⋅ 4π R 2 = dt L

235

(11)

236

Eq. (11) shows that the release rate of coated fertilizer is proportional to the Pe of the coated film

237

and the saturated solubility of nutrients. Therefore, the release rate of coated fertilizer with

238

single-component can be easily controlled by the film coating amount, according to the uptake

239

rate of nutrient by crops.

240 241

3.2 Diffusion performance of N-K and N-P double-component fertilizer solution

242

The concentration of each nutrient in urea-KCl and urea-NH4H2PO4 saturated solution was

243

measured and reported in Table 5. It indicates that the saturated concentration of each nutrient in

244

the double-component solution is lower than that when the nutrient exists alone in the solution,

245

and the concentration of urea is higher than that of KCl and NH4H2PO4 respectively. Specifically,

246

for urea-KCl saturated solution, the mass of urea dissolved in the solution is 95% of that when

247

urea exists alone, and for KCl, it is only 56%. The ratio of nutrient concentration in saturated

248

solution is measured to be N:K2O=2.64. For urea-NH4H2PO4 saturated solution, the mass of urea

249

dissolved in the solution is 87% of that when urea exists alone, and for NH4H2PO4, it is only 53%.

250

The ratio of nutrient concentration in saturated solution is measured to be N:P2O5=2.46. This is


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251

because urea and water can easily form hydrogen bonds in the solution, which lowers the mobility

252

of water molecules25, 26. Therefore, when the other nutrient is present, the saturated solubility of

253

urea is not significantly reduced. However, due to the decrease in hydration and dissolution of KCl

254

and NH4H2PO4 by water molecules, the saturated solubility of KCl and NH4H2PO4 significantly

255

decreased.

256

Table 5. Saturated concentration of each nutrient in urea-KCl and urea-NH4H2PO4 composite

257

solutions Saturated solution

258

Concentration of nutrient (g/L)

Nutrient ratio

urea-KCl

urea: 601 (95% sat)

KCl: 168 (56% sat)

N:K2O=2.64

urea-NH4H2PO4

urea: 542 (87% sat)

NH4H2PO4: 181 (53% sat)

N:P2O5=2.46

Note: “sat” means the saturated concentration of nutrient in the solution when it exists alone

259

The permeation coefficient Pe of each nutrient in different fertilizer solutions was measured

260

and reported in Table 6. In the urea-KCl saturated solution, the urea molecule interacts with K+

261

and Cl- to form complex molecules27, which has a relatively large size. A small proportion of the

262

urea diffused through the film in the form of complex molecules, which have a higher diffusion

263

resistance and a lower permeation coefficient. A majority of the urea diffuses in the form of urea

264

molecules. So the permeation coefficient of urea in composite solution is lower than that of

265

saturated urea solution. For the KCl solution, all of K+ and Cl- diffuses through the film in the

266

form of complex molecules, so the permeation coefficient of KCl in composite solution is much

267

lower than that of saturated KCl solution. In the urea-NH4H2PO4 saturated solution, the urea

268

molecules interact with H2PO4- to form complex molecules28. So the permeation coefficient of

269

urea and NH4H2PO4 in composite solution is lower compared with that when one component

270

exists alone in the saturated solution. As a result, the release rate of N is much faster than K and P

271

due to the interaction between nutrients.



Page 14 of 22

Table 6. Permeation coefficient of each nutrient in different fertilizer solutions

272

Permeation coefficient of nutrient (10-18 m2/s)

Saturated solution urea

urea: 519

-

-

KCl

-

KCl: 251

-

NH4H2PO4

-

-

NH4H2PO4: 2.18

urea-KCl

urea: 323

KCl: 35.7

-

urea-NH4H2PO4

urea: 273

-

NH4H2PO4: 1.27

273

The nutrient release rate ratio was determined by measuring the mass of nutrient in the

274

receiving side and reported in Table 7. Due to the difference in solubility and permeation

275

coefficient of each nutrient, the release rates of different nutrient differ significantly. For the

276

urea-KCl saturated solution, the nutrient release rate ratio is measured to be N:K2O=23.6. For

277

urea-NH4H2PO4 saturated solution, the nutrient release rate ratio is measured to be N:P2O5=486.4.

278

This means the release rate of N is much faster than that of K and P. That is to say, for the coated

279

fertilizer with urea-KCl and urea-NH4H2PO4 composition, after most of the urea released, KCl or

280

NH4H2PO4 would begin to release in large quantities.

281

Table 7. Nutrient release rate ratio in urea-KCl and urea-NH4H2PO4 saturated solutions Saturated solution

Nutrient release rate ratio

urea-KCl

N:K2O=23.6

urea-NH4H2PO4

N:P2O5=486.4

282 283

3.3 Diffusion performance of N-P-K multi-component fertilizer solution

284

The concentration of each nutrient in N-P-K saturated solution was measured and reported in

285

Table 8. It indicates that the saturated concentration of each nutrient in the multi-component

286

fertilizer solution is lower than that when the nutrient exists alone in the solution, and due to the

287

difference in affinity of different nutrients to water, the solubility of different nutrients are

288

different.


Page 15 of 22


289

Table 8. Saturated concentration of each nutrient in N-P-K composite solution Concentration of nutrient (g/L) Saturated solution

290

NH4Cl

NH4H2PO4 / (NH4)2HPO4

KCl / K2SO4

NH4Cl-NH4H2PO4-KCl

206 (66% sat)

54 (16% sat)

123 (41% sat)

NH4Cl-(NH4)2HPO4-KCl

205 (65% sat)

130 (26% sat)

113 (37% sat)

NH4Cl-NH4H2PO4-K2SO4

260 (83% sat)

60 (18% sat)

98 (85% sat)

NH4Cl-(NH4)2HPO4-K2SO4

243 (78% sat)

128 (26% sat)

88 (76% sat)

Note: “sat” means the saturated concentration of nutrient in the solution when it exists alone

291

The nutrient concentration ratio in N-P-K saturated solution and the release rate ratio of the

292

nutrient through the film were measured and reported in Table 9. It shows that among different

293

solutions, since (NH4)2HPO4 has a higher solubility and N content is higher than NH4H2PO4, the

294

solution taking (NH4)2HPO4 as the source of phosphorus has the relative high contents of N and P

295

compared with that of NH4H2PO4. Because the solubility and permeation coefficient of different

296

nutrients are different, there is a big difference among the release rates of different nutrients. For

297

NH4Cl-NH4H2PO4-KCl saturated solution, the release rate was in the order of K2O > N > P2O5. It

298

was analyzed that the highest concentration and smallest size of K+ resulted in the fastest release

299

rate of K+. For NH4Cl-(NH4)2HPO4-KCl saturated solution, the release rate was in the order of N >

300

K2O > P2O5. It was analyzed that (NH4)2HPO4 can provide more NH4+ in the solution, the

301

enhancement in driving force derived from the concentration gradient makes that the release rate

302

of NH4+ is faster than that of K+. In the case of solid nutrient ratio prepared being

303

N:P2O5:K2O=1:1:1, for NH4Cl-NH4H2PO4-K2SO4 saturated solution, the release rate was in the

304

order of K2O > N > P2O5, and for NH4Cl-(NH4)2HPO4-K2SO4 saturated solution, the release rate

305

was in the order of N > K2O > P2O5. In all solutions, as the concentration of phosphate is the

306

lowest and its size is the biggest, the release rate of P2O5 is the slowest. It shows that the selection

307

of phosphorus source and potassium source has a great influence on the release rate of nutrients.



308

Page 16 of 22

Table 9. Ratio of nutrient concentration and release rate in N-P-K saturated solution

Saturated solution

Nutrient concentration ratio (N:P2O5:K2O)

Nutrient release rate ratio (N:P2O5:K2O)

NH4Cl-NH4H2PO4-KCl

0.78:0.43:1

0.60:0.58:1

NH4Cl-(NH4)2HPO4-KCl

1.14:0.98:1

30.9:0.52:1

NH4Cl-NH4H2PO4-K2SO4

1.42:0.70:1

0.23:0.13:1

NH4Cl-(NH4)2HPO4-K2SO4

1.91:1.44:1

11.8:0.12:1

309

The diffusion performance of nutrients in the double and triple component fertilizer solutions

310

indicated that there are significant differences among the release rate of different nutrients. In the

311

double and triple component saturated solution, the freedom degree of the solution is 0, so the

312

release rate of each nutrient is a fixed value, it is not possible to change the release rate by

313

adjusting the nutrient independently. So the difference in the demands for N, P, and K of different

314

crops can not be matched. Therefore, in order to meet the demands of different nutrients for crops,

315

compared with fertilizing coated compound fertilizer, coating the single-component fertilizer, i.e.,

316

nitrogen fertilizer, phosphate fertilizer and potash fertilizer, and blending them according to the

317

corresponding nutrient needs of crops can adjust the nutrient release rate more flexibly.

318 319

Conflict of interest

320

The authors declare no competing financial interest.

321 322 323 324 325 326

References (1) Hanafi, M. M.; Eltaib, S. M.; Ahmad, M. B. Physical and chemical characteristics of controlled release compound fertiliser. Eur. Polym. J. 2000, 36, 2081-2088. (2) Easton, Z. M.; Petrovic, A. M. Fertilizer source effect on ground and surface water quality in drainage from turfgrass. J. Environ. Qual. 2004, 33, 645-655.


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(3) Shaviv, A. Advances in controlled-release fertilizers. Adv. Agron. 2001, 71, 1-49.

328

(4) Shaviv, A.; Raban, S.; Zaidel, E. Modeling controlled nutrient release from polymer coated

329

fertilizers: diffusion release from single granules. Environ. Sci. Techno. 2003, 37, 2251-2256.

330

(5) Huett, D. O.; Gogel, B. J. Longevities and nitrogen, phosphorus, and potassium release patterns of

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polymer-coated controlled-release fertilizers at 30 oC and 40 oC. Commun. Soil. Sci. Plan. 2000, 31,

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959-973.

333

(6) Broschat, T. K.; Moore, K. K. Release rates of ammonium-nitrogen, nitrate-nitrogen, phosphorus,

334

potassium, magnesium, iron, and manganese from seven controlled-release fertilizers. Commun. Soil.

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Sci. Plan. 2007, 38, 843-850.

336 337 338 339

(7) Lu, P.; Zhang, M.; Li, Q.; Xu, Y. Structure and properties of controlled release fertilizers coated with thermosetting resin. Polym.-plast. Technol. 2013, 52, 381-386. (8) Du, C.; Zhou, J.; Shaviv, A. Release characteristics of nutrients from polymer-coated compound controlled release fertilizers. J. Polym. Environ. 2006, 14, 223-230.

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(9) Noppakundilograt, S.; Pheatcharat, N.; Kiatkamjornwong, S. Multilayer-coated NPK compound

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fertilizer hydrogel with controlled nutrient release and water absorbency. J. Appl. Polym. Sci. 2015, 132,

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41249.

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(10) Lan, R.; Liu, Y.; Wang, G.; Wang, T.; Kan, C.; Jin, Y. Experimental modeling of polymer latex spray coating for producing controlled-release urea. Particuology 2011, 9, 510-516. (11) Silcock, H. Solubilities of inorganic and organic compounds: Ternary and multi-component systems of inorganic substances; Pergamon Press: Oxford, U.K., 1979. (12) Ussing, H. H.; Zerahn, K. Active transport of sodium as the source of electric current in the short-circuited isolated frog skin. Acta Physiol. Scand. 1951, 23, 110-127.



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(13) Yang, L.; An, D.; Wang, T.; Kan, C.; Jin, Y. Swelling and diffusion model of a hydrophilic film coating oncontrolled-release urea particles. Particuology 2017, 30, 73-82. (14) Skoog, D. A.; Holler, F. J.; Nieman, T. A. Principles of instrumental analysis; Saunders College Publishing: Harcourt Brace, Orlando, FL, 1998. (15) Wijmans, J.; Baker, R. The solution-diffusion model: a review. J. Membrane Sci. 1995, 107, 1-21.

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(16) Wang, J.; Dlamini, D.; Mishra, A.; Pendergast, M.; Wong, M.; Mamba, B.; Freger, V.; Verliefde,

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A.; Hoek, E. A critical review of transport through osmotic membranes. J. Membrane Sci. 2014, 454,

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516-537.

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(17) Garbarini, G.; Eaton, R.; Kwei, T.; Tobolsky, A. Diffusion and reverse osmosis through polymer membranes. J. Chem. Educ. 1971, 48, 226-230. (18) Deen, W. Hindered transport of large molecules in liquid-filled pores. AIChE J. 1987, 33, 1409-1425. (19) Sharma, J.; Tewari, K.; Arya, R. K. Diffusion in polymeric systems-A review on free volume theory. Prog. Org. Coat. 2017, 111, 83-92. (20) Gosting, L. J.; Akeley, D. F. A study of the diffusion of urea in water at 25 oC with the gouy interference method. J. Am. Chem. Soc. 1952, 74, 2058-2060.

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(21) Robinson, R. A. Stokes R H. Electrolyte solutions; Dover Publications: New York, 1959.

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(22) Schultz, S. G.; Solomon, A. Determination of the effective hydrodynamic radii of small

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molecules by viscometry. J. Gen. Physiol. 1961, 44, 1189-1199.

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(23) Tansel, B.; Sager, J.; Rector, T.; Garland, J.; Strayer, R.; Levine, L.; Roberts, M.; Hummerick, M.;

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Bauer, J. Significance of hydrated radius and hydration shells on ionic permeability during


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nanofiltration in dead end and cross flow modes. Sep. Purif. Technol. 2006, 51, 40-47.

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(24) Collins, K. D. Sticky ions in biological systems. P. Natl. Acad. Sci. USA, 1995, 92, 5553-5557.

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(25) Ramondo, F.; Bencivenni, L.; Caminiti, R.; Pieretti, A.; Gontrani, L. Dimerisation of urea in

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water solution: a quantum mechanical investigation. Phys. Chem. Chem. Phys. 2007, 9, 2206-2215. (26) Rezus, Y. Bakker, H. Effect of urea on the structural dynamics of water. P. Natl. Acad. Sci. USA, 2006, 103, 18417-18420. (27) Hong, J. Capp, M. W.; Anderson, C. F.; Record, M. T. Preferential interactions in aqueous solutions of urea and KCl. Biophys. Chem. 2003, 105, 517-532.

379

(28) Palecz, B.; Grala,; A.; Kudzin, Z. Calorimetric studies of the interactions between several

380

aminophosphonic acids and urea in aqueous solutions at 298.15 K. J. Chem. Eng. Data, 2014, 59,

381

426-432.



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For Table of Contents Only The way of single-component fertilizers’ coating and their bulk blending can match the nutrient uptake rate of the crop.

Mass of KNO3 (mg/m2)

140

(b)

120

Data Linear fit of steady stage, R2=0.999

100 80 60 40 20 0 0

5

10

15

20

Time (h)


25

30

Page 21 of 22


Figure 1. Schematic diagram of the Ussing chamber 1. Supply side: saturated solution, 2. Film, 3. Receiving side: ultrapure water, 4. Clip 228x134mm (72 x 72 DPI)



Figure 2. Mass of different nutrient diffused to the receiving side vs time (a) KCl, (b) KNO3, (c) K2SO4, (d) NH4Cl, (e) (NH4)2SO4, (f) (NH4)2HPO4, (g) NH4H2PO4, (h) urea 389x605mm (72 x 72 DPI)


Page 22 of 22

Diffusion Performance of Fertilizer Nutrient through ... - ACS Publications

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