American Journal of Plant Sciences, 2013, 4, 1976-1982
http://dx.doi.org/10.4236/ajps.2013.410245 Published Online October 2013 (http://www.scirp.org/journal/ajps)
Effect of Ammonium- and Potassium-Loaded Zeolite on
Kale (Brassica alboglabra) Growth and Soil Property
Junxi Li1,2*, Chido Wee1, Bokyoon Sohn1
1Department of Agricultural Chemistry, Sunchon National University, Suncheon, South Korea; 2School of Biology and Biotechnol-
ogy Sciences, Murdoch University, Perth, Australia.
Received August 1st, 2013; revised September 5th, 2013; accepted September 23rd, 2013
Copyright © 2013 Junxi Li et al. This is an open access article distributed under the Creative Commons Attribution License, which
permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
We investigated the feasibility of using ammonium- and potassium-loaded zeolite (NK-Z) as carriers for fertilizer and
for slow release of nitrogen (N) and potassium (K). Plant growth response and soil analysis were performed. The results
indicated an increase in the total harvest weight of kale (Brassica alboglabra Bailey). Furthermore, higher levels of N
and K were detected in soil applied with NK-Z than in soil applied with compound fertilizers. The leaf fresh weight of
kale in the fertilizer treatments including NK-Z were 2118.4 and 2111.3 g·plant−1, while the leaf fresh weights of kale in
the treatment without NK-Z was 2018.0 g·plant−1. The N and K contents in the soils were maintained in the high level
in the NK-Z treatment compared that in control treatment. The results indicate that NK-Z has a great potential as the
slow-release fertilizer reducing pollution by preventing leaching to the ground water.
Keywords: Zeolite; Slow-Release Fertilizer; Soil Property; Kale; Growth Response
1. Introduction
Zeolites have been used in commercial applications be-
cause of their unique adsorption, ion-exchange, molecu-
lar sieve, and catalytic properties. In agricultural field,
natural zeolite can be provided in large quantities with
uniform characteristics and unique properties (cation ex-
change capacity and pH) for application and commercial
processing [1]. The negative charge created when Al3+
replaces Si4+ in structural tetrahedra is counterbalanced
by cations (e.g., Na+, K+, 4
NH

, and Ca2+, Mg2+). These
charge sites are located in large structural channels and
cavities throughout the structure and will be referred to
as zeolitic exchange sites. Due to this special structure,
natural zeolite can adsorb many kinds of ions with vary-
ing degrees of ability. Natural zeolite is highly selective
for 4 and K+ relative to Na+ or divalent cations such
as Ca2+ and Mg2+ due to the location and density of nega-
tive charge in the structure and the dimensions of interior
channels (0.40 - 0.72 nm diameter) [2].
NH
Natural zeolites in soil help to retain nutrients and im-
prove long-term soil quality by enhancing its absorption
ability. It influences soil retention of the most important
plant nutrients such as N and K, Ca, Mg, and many kinds
of micro-elements. Zeolite can retain these nutrients in
the root zone to be used by plants as needed. The appli-
cation of natural zeolite also enhances plant growth and
reduces nutrient loss. Many laboratory and field expe-
riments carried in recent decades have shown that sur-
factant-modified zeolite and nutrient-loaded zeolite can
be used as a kind of slow-release fertilizer to supply long-
lasting nutrients for crop growth [3,4]. The application of
zeolite can enhance the plant growth and development by
reducing the loss of nutrients. The main use of natural
zeolites in agriculture is for ammonium (4) exchange,
storage, slow release and decrease losses of nitrogen
through nitrification.
NH
Nitrogen leaching from irrigated cropland significantly
contributes to increased nitrate (3) levels in ground
and surface water [5]. To overcome the problems associ-
ated with nitrogen leaching during fertilizer application,
different approaches were taken to control N release. Ge-
nerally, slow-release fertilizers (SRF) are usually expen-
sive, and the release of N is slow at the time of high N
need. However, in a 4-week long experiment, Perrin et al.
[6] reported that soil amendment with ammonium-loaded
clinoptilolite (A-CP) significantly reduced leaching and
provided sufficient N for normal corn growth. However,
corn begins to take up exponentially higher levels of N
NO 
*Corresponding author.

Effect of Ammonium- and Potassium-Loaded Zeolite on Kale (Brassica alboglabra) Growth and Soil Property 1977
approximately 4 weeks after emergence [7]. Thus, Perrin
et al. did not analyze whether A-CP released sufficient
amounts of N to meet the N requirement of corn during
the entire growth period.
Kale (Brassica alboglabra Bailey) is one of the most
commonly grown vegetables in South Korea. The pur-
pose of this study was to investigate the growth charac-
teristics of kale and the feasibility of using NK-Z as car-
riers for fertilizer and for slow release of N and K.
2. Materials and Methods
2.1. Zeolite
Natural zeolites used in this experiment were purchased
from Handu Co. Korea at a size of 1 - 2 mm in diameter.
The constitution of the natural zeolite used in this ex-
periment is shown in Table 1. The natural zeolite mainly
consisted of SiO2 and Al2O3, which comprised 70.3%
and 13.6% of the total elements. Because of the high ca-
tion exchange capacity (CEC), this kind of natural zeolite
is a good carrier for cation. The zeolite layer was collec-
ted from the bottom of the autoclave during the hydro-
thermal process, and the structure was characterized us-
ing X-ray diffraction (XRD, D/Max-2500V/PC, PANaly-
tical B.V.) analysis. The natural zeolites used in this ex-
periment were confirmed as Mordenite (33%), Muscovite
(37%) and Clinoptilolite (30%).
2.2. Production of Ammonium- and
Potassium-Loaded Zeolite
Ammonium-loaded zeolite (NZ) and potassium-loaded
zeolite (KZ) were produced using the method of Perrin et
al. [4] with minor modification. Natural zeolite particles
were loaded with 4 and K+ by soaking in 1M ammo-
nium sulfate ((NH4)2SO4) and 1M potassium chloride
(KCl), respectively, for10 days. NZ and KZ were rinsed
with water until the electrical conductivity (EC) of the
supernatant was <0.5 mSm−1 [4]. Total N content in NZ
was analyzed using the Kjeldahl digestion method [8],
and Total K content in KZ was analyzed using inductive
NH
coupled plasma-mass spectrometry (ICP, Optima 3300
DV, Perkin-Elmer, USA). The NZ and KZ fertilizers
(NK-Z) so produced contained 2% N and 3% K, respec-
tively.
2.3. Tested Crops and Farming Methods
Kale (Brassica alboglabra Bailey) was selected as the
test plant and cultured as seedlings in a greenhouse. The
characteristics of soil and the kale were tested before the
kale transplanting (Tables 2 and 3). Approximately 200
kg/10a lime and 1500 kg/10a compost were mixed in the
soil because of the low fertility of the soil. In each treat-
ment, the compound fertilizer or NK-Z was broadcasted
on the field uniformly and mixed with the soil using cul-
tivator.
The growth characteristics of kale and changes in ni-
trogen and potassium concentrations in soil were inves-
tigated regularly after application of NK-Z. Three kinds
of fertilizers were used in this experiment: (1) compound
fertilizer as basal conventional fertilizer along with addi-
tional fertilizer (CF), (2) compound fertilizer as the basal
conventional fertilizer and NK-Z as the additional fertil-
izer (ZAF), and (3) NK-Z as the basal and additional fer-
tilizer (ZBAF). The concentrations of N, P and K be-
tween compound fertilizer and NK-Z fertilizer had no
differences among every treatments. The experiment area
for every treatments were 2.4 m2, 100 g compound ferti-
lizer (N-P-K = 11-10-8 kg/10a) were added into the soil
in the treatment of CF. In the treatment of ZAF, 100 g
compound fertilizer (N-P-K = 11-10-8 kg/10a) were add-
ed into the soil as conventional fertilizer, 1425 g N-Z and
263 g K-Z were added as additional fertilizer, NK-Z as
additional fertilizer were added into the soil at the same
time with the application of basal fertilizer before seed-
ling transplanting. In the treatment of ZBAF, the NK-Z
were also added into the soil before seedling transplant-
ing. 2200 g N-Z, 405 g K-Z, and 36 g superphosphate (P
= 20%) were added into soil as basal and additional fer-
tilizer.
Table 1. Chemical characteristics of natural zeolite used in the experiment.
SiO2
(%)
Al2O3
(%)
Fe2O3
(%)
CaO
(%)
MgO
(%)
Na2O
(%)
K2O
(%)
P2O5
(%)
Moisture
(%)
Specific
gravity
CEC
cmol+ kg−1
70.3 13.6 1.29 2.51 0.31 1.93 3.17 0.09 6.80 2.04 68.29
Table 2. The characteristics of experimental soil.
Ex. Cations
(cmol+ kg−1) pH
(1:5)
EC
(dSm−1)
O.M
(g·kg−1)
Av.P2O5
(mg·kg−1)
K Ca Mg
C.E.C
(cmol+ kg−1)
5.7 0.81 28 643 1.8 4.9 2.1 10.8

Effect of Ammonium- and Potassium-Loaded Zeolite on Kale (Brassica alboglabra) Growth and Soil Property 1978
Table 3. The growth characteristics of kale before trans-
planting.
Species No. of
leaves (ea)
Leaf
area (cm2)
Shoot
fresh weight (g)
Brassica alboglabra
Bailey 5.0 ± 0.0 112.25 ± 1.96 8.02 ± 0.26
2.4. Test Methods and Statistical Analysis
Soil in the different treatment fields were sampled 0, 3, 6,
and 18 weeks after transplanting, Weight 5 g dry soil into
a plastic triangular flask, add 50 ml distilled water and
shake for 30 minutes at the speed of 120 rpm. The clear
solution was accepted after filtering using what man
No.2 filter paper. The nitrogen content was analyzed by
the Kjeldahl digestion method [8] and potassium was
analyzed by Inductive Coupled Plasma (ICP, Optima
3300 DV, Perkin-Elmer, USA) using the method of NI-
AST [9]. EC and pH were analyzed using Istek Conduc-
tivity meter and Mettler Toledo 340 pH meter, respec-
tively. Phosphorus and Soil CEC were also analyzed us-
ing the method of NIAST [9].
Chlorophyll content of fully expanded kale leaves was
measured using an in situ SPAD-502 chlorophyll meter
(Minolta Co. Ltd., Japan). Actual chlorophyll content Y
(mg/100 cm2) was calculated by substituting the SPAD
reading for X in the standard formula Y = 0.0996X −
0.152 [10]. Leaf length and leaf width were measured us-
ing vernier caliper, shoot weight were measured using
platform balance (A&D HF-2000 g). For chemical analy-
sis, plant samples were finely ground after drying at 65˚C
for 48 h. A 0.5 g sample was placed in a 100 ml flask
with 10 ml of concentrated H2SO4. Next, 0.5 ml H2O2
was added to the sample every 10 min for 90 min (total:
4.5 ml). After cooling, the solution was filtered through a
Whatman No. 6 filter into 100 ml flasks. Inorganic con-
stituents contents were determined using Inductive Cou-
pled Plasma (ICP, Optima 3300DV, Perkin-Elmer, USA).
The data from different treatment combinations were ana-
lyzed using SPSS for windows.
3. Results and Discussion
3.1. Crop Growth Characteristics
Significant increases in the yields of wheat (13% - 15%),
eggplant (19% - 55%), apples (13% - 38%), and carrots
(63%) were reported when 4 - 8 tons of zeolite were
added per acre [11]. In our study, leaf number, leaf
length, leaf width, shoot weight, and chlorophyll content
were estimated three weeks after transplanting (Table 4).
The leaf length of kale in ZAF and ZBAF were 12.61%
and 9.28% longer, respectively, than in CF. However, the
leaf number did not differ significantly among the groups.
The shoot weight in ZAF and ZBAF was 3.74% and
3.61% higher, respectively, than in CF. Thus, the results
indicate that NK-Z enhances plant growth during the ear-
ly stage.
The leaf fresh weight per plant was estimated at 6 in-
tervals of harvesting. NK-Z improved the harvest of kale
significantly; the yield in ZAF and ZBAF was 4.97% and
4.65% higher, respectively, as compared with CF (Fig-
ure 1). It has been reported that leaf area, dry weight,
and root fresh weight was higher in radishes fertilized
with A-CP than in those fertilized with ammonium sul-
fate [12]. In this experiment, we showed that plant growth
and kale harvest was higher both in ZAF and ZBAF as
compared to that in CF.
3.2. Inorganic Matter Contents in Kale Leaf
There was rare experiment adjustment the effective of
zeolite on crop inorganic matter contents. In this paper,
we tested the inorganic matter contents between every
group in the kale leaf to investigate the effective of nutri-
tion loaded zeolite on improving crop inorganic matter
contents 18 weeks after transplanting (Table 5). In the
group of ZAF, all of the tested inorganic constituents
Table 4. Growth responses of kale 3 weeks after trans-
planting.
Treatments
No. of
leaves
(ea)
Shoot
weight
(g/plant)
Leaf
length
(cm)
Leaf
width
(cm)
Chlorophyll
contents
(mg/100 cm2)
CF* 9.58141.24 19.83 18.50 4.67
ZAF* 9.41146.52 22.33* 19.67 4.89
ZBAF* 9.69146.34 21.67 19.33 4.92
LSD 0.05*0.379 25.9711.972 2.568 0.386
*CF, Compound fertilizer as basal conventional fertilizer along with addi-
tional fertilizer; *ZAF, Compound fertilizer as basal conventional fertilizer,
NK-Z as additional fertilizer; *ZBAF, NK-Z as basal and additional fertilizer.
*Each value was compared with least significant difference (LSD).
0
500
1000
1500
2000
2500
CFZAF ZBAF
Treatment group
Leaf fresh wight(g/plant)
1 st harvesting2nd harvesting3rd harvesting
4th harvesting5th harvesting6th harvesting
Figure 1. The fresh weight of kale leaf via 6 times of har-
vesting.

Effect of Ammonium- and Potassium-Loaded Zeolite on Kale (Brassica alboglabra) Growth and Soil Property 1979
contents (CaO, K2O, MgO, Na2O) in kale leaf were sig-
nificantly higher than that in the group of CF, especially
the Na2O content which was 50% higher than CF. In the
group of ZBAF, the K2O, MgO and Na2O contents were
remarkably higher than that in the treatment of CF. From
the data above, we indicated that both ZAF and ZBAF
improved the contents of inorganic constituents in kale
leaf.
3.3. The Physicochemical Property Change of
Soil
The addition of zeolites usually increases pH levels [13].
However, in this experiment, there were no significant
differences between compound fertilizer and NK-Z fer-
tilizer on the soil pH (Table 6). Available phosphorus
(av-P) contents of CF group were 655.49 mg·kg−1 before
experiment and was 494.78 mg·kg−1 at the end of the
experiment. However, in ZBF group. The av-P contents
were 516.03 mg·kg−1 after the experiment. That because
NK-Z, as a kind of slow-release fertilizer, could adsorb P
and release to soil slowly when crop needed, which lead
to the less losing of P.
CEC and exchangeable cation contents (Ca2+ K+ Mg2+
Na+) in soil were analyzed in the last stage of plant
growth (Table 7). The exchangeable cation contents and
CEC had no significant differences among the three
treatments. This was probably because of the same nu-
trients and the same cultivator methods were used in
every treatment. The results indicate that NK-Z had no
significant differences with the traditional chemical fer-
tilizers on improving exchangeable cation contents and
soil CEC. But the utility of NK-Z as a slow-release fer-
tilizer on reducing the leaching speed of nitrogen and
potassium was very important and would be discussed in
the following.
3.4. Nitrogen and Potassium Movement in Soil
The dynamics of exchangeable and water-soluble NH4-N
in soil is shown in Figure 2. During the first 3 weeks, the
downward trend of exchangeable and water-soluble NH4-
N was more apparent in the ZAF and ZBAF treatment
group than in CF treatment group, probably because of
an absence of additional compound fertilizer in the for-
mer groups. A significant difference was observed in the
NH4-N concentration among the various amendment treat-
ments at all sampling dates, and the exchangeable NH4-N
concentrations for all groups were less than 200 mg·kg−1,
6 weeks after incubation. Eighteen weeks after trans-
planting ZAF and ZBAF applied soils appeared to main-
tain relatively higher NH4-N concentrations. This was
probably due to retention of 4 on cation-exchange
sites of the zeolite. The exchangeable NH4-N concentra-
tions in ZAF and ZBAF were 8.22% and 45.40% higher,
respectively, than in CF, while water-soluble NH4-N con-
centrations in ZAF and ZBAF were 1.71% and 5.95% hi-
gher, respectively, than in CF.
NH
During the first 3 weeks, the downward trend in the
exchangeable and water-soluble NO3-N concentrations
Table 5. Inorganic constituents contents in kale leaf 18
weeks after transplanting.
Treatments CaO
(%)
K2O
(%)
MgO
(%)
Na2O
(%)
CF* 2.40 1.10 0.39 0.18
ZAF* 2.59* 1.29* 0.46* 0.27*
ZBAF* 2.43 1.34* 0.46* 0.24*
LSD 0.05* 0.073 0.049 0.013 0.009
*CF, Compound fertilizer as basal conventional fertilizer along with addi-
tional fertilizer; *ZAF, Compound fertilizer as basal conventional fertilizer,
NK-Z as additional fertilizer; *ZBAF, NK-Z as basal and additional fertilizer.
*Each value was compared with least significant difference (LSD).
Table 6. The physicochemical property changement of soil.
pH EC (dS m−1) av-P2O5 (mg·kg−1)
CF ZBF ZBAF CF ZBF ZBAF CF ZBF ZBAF
Before 6.70 6.68 6.66 0.58 0.58 0.56 655.49 618.94 621.05
After 6.57 6.57 6.55 0.56 0.57 0.55 494.78 516.03 478.66
Before: Soils sampled before experiment; After: Soils sampled after experiment.
Table 7. Exchangeable cation contents and cation exchange capacity in soil.
Treatments Ca
(cmol+ kg−1)
K
(cmol+ kg−1)
Mg
(cmol+ kg−1)
Na
(cmol+ kg−1)
CEC
(cmol+ kg−1)
CF* 3.08 0.60 0.22 4.75 14.21
ZAF* 3.32 0.59 0.20 5.03 14.49
ZBAF* 3.07 0.57 0.19 4.81 14.71
LSD 0.05* 0.206 0.013 0.008 0.239 0.582
*CF, Compound fertilizer as basal conventional fertilizer along with additional fertilizer; *ZAF, Compound fertilizer as basal conventional fertilizer, NK-Z as
additional fertilizer; *ZBAF, NK-Z as basal and additional fertilizer. *Each value was compared with least significant difference (LSD).

Effect of Ammonium- and Potassium-Loaded Zeolite on Kale (Brassica alboglabra) Growth and Soil Property 1980
0
300
600
900
0510 15 20
Elapsed weeks
NH4-N concentration(mg kg-1)
CF
ZAF
ZBAF
(a)
60
80
100
120
051015 20
Elapsed weeks
D.W. extracted NH4-N(mg kg
-1) CF
ZAF
ZBAF
(b)
Figure 2. The dynamics of NH4-N concentrations in soils.
because of nitrification was more pronounced in ZAF
and ZBAF than in CF (Figure 3). The decrease in ex-
changeable NO3-N concentration in ZAF and ZBAF is
probably because of the retention of 4
N
H on the zeolite,
which decreased the availability of 4
N
H for nitrification.
The concentration of both exchangeable and water-solu-
ble NO3-N decreased gradually after 6 weeks. Eighteen
weeks afterwards, the exchangeable NO3-N concentra-
tion in ZAF and ZBAF was 3.16% and 19.87% higher
than in CF, and the water-soluble NO3-N concentration
in ZAF and ZBAF were 1.32% and 27.12% higher, re-
spectively, than in CF.
Clinoptilolite zeolite has been used to reduce NH3
emission from farm manures and as an 4
N
H

-loaded
exchange fertilizer because of its high CEC [14]. NK-Z
has been shown to be an excellent long-term slow-release
fertilizer when applied to agricultural crops. In loamy
sand (6% clay), the decrease in 3 leaching by A-CP
treatment was 30% more than that by compound fertil-
izer treatment [12]. Perrin hypothesized that A-CP re-
NO 
0
1000
2000
3000
05101520
Elapsed weeks
NO3-N concentration(mg kg-1)
CF
ZAF
ZBA
(a)
0
500
1000
1500
0510 1520
Elapsed weeks
D .W. extracted N O3-N(mg kg
-1)
CF
ZAF
ZBAF
(b)
Figure 3. The dynamics of NO3-N concentrations in soils.
duced N leaching while increasing N-use efficiency com-
pared to compound fertilizer [4]. However, the experi-
ment was terminated after approximately 4 weeks, and
they did not collect data pertaining to the last stage of
crop growth. In our experiment, the N concentrations
were estimated throughout the growth period of crops,
and hence, we could observe the constantly changing trend
of N concentration.
Natural zeolite can be used both as a carrier of nutri-
ents (e.g., 4
N
H

and K+) as well as a medium of free ex-
changeable nutrient ions. Some natural zeolites contain
considerable amounts of exchangeable K+ that can en-
hance plant growth. Only a few studies have compared
the K leaching from K-saturated clinoptilolite and KNO3,
pointing out the advantages of the zeolite as and slow-
release fertilizers [15]. In this experiment, the plot of K
concentrations is shown in Figure 4. Both exchangeable
and water-soluble K concentration decreases sharply in
the first 3 weeks and stabilize thereafter. Despite the hi-
gher K+ retention, the release pattern of ZAF and ZBAF
is similar to that in CF, but at the later stage, i.e.,

Effect of Ammonium- and Potassium-Loaded Zeolite on Kale (Brassica alboglabra) Growth and Soil Property 1981
0
2
4
6
0510 1520
Elapsed days
K concentration(cmol+ kg-1)
CF
ZAF
ZBAF
(a)
0. 00
0. 25
0. 50
0. 75
1. 00
0510 1520
Elapsed days
D.W. extracted K(cmol + kg-1)
CF
ZAF
ZBAF
(b)
Figure 4. The dynamics of K concentrations in soils.
18 weeks after transplanting, the exchangeable K con-
centrations were 12.85% and 34.08% higher and the wa-
ter-soluble K were 39.87% and 58.37% higher, respec-
tively, than that of CF. The K concentrations in ZAF and
ZBAF were higher than that in CF on each of the inves-
tigation days, which indicate that NK-Z as a kind of
slow-release fertilizer can maintain the high level of K
throughout the growth period until the final stage of plant
development.
Unlike compound fertilizers, ZAF and ZBAF provided
controlled release of available N and K, and thus can
serve as slow-release fertilizers. The slow release of N
and K from NK-Z at late stage was probably due to the
diffusion and cation exchange [16], processes that con-
trol the release of N and K from NK-Z. According to the
results above, we also suggest that NK-Z can be used as
slow-release fertilizers because of its long-lasting nutri-
ent-keeping ability.
4. Conclusion
Many studies have been conducted to develop nitrogen
best management practices (BMPs) to increase N utiliza-
tion efficiency and to reduce N losses via leaching or vo-
latilization. Zeolite has been used to reduce NH3 emis-
sion from farm manures and as 4
N
H-loaded exchange
fertilizer because of its high CEC [4,14].
In this study, we indicated that NK-Z can maintain the
requisite N and K levels during the entire period of crop
growth compared with the compound fertilizer. Kale
grown in soil applied with NK-Z assimilated significant-
ly higher levels of Na, Mg, and K than kale grown in soil
applied with CF. According to the result of ZAF and
ZBAF, we indicated that NK-Z as basal fertilizer and ad-
ditional fertilizer was more effective on crop growth.
That means NK-Z, not as a compound fertilizer adjunct
agent, can be applied into soil instead of compound fer-
tilizer. NK-Z can not only be used as a slow-release fer-
tiliser for sustaining plant growth and also provide a nu-
trient supply that is high enough to sustain suitable plant
development. Furthermore, the use of NK-Z provides a
long-lasting reservoir of nutrients, which reduces the
need of adding fertilization while achieving better crop
performance. Another important advantage is that NK-Z
as additional fertilizer can be added into soil before seed-
ling transplanting because of their slow-release character,
which can reduce lots of labour force for the application
of additional fertilizer. The product is environmentally
safe as well. Unlike the commonly used fertilizers, the
use of NK-Z can dramatically reduce the loss of nutrients
to ground water and the environment.
5. Acknowledgements
This study was supported by the Technology Develop-
ment Program for Agriculture and Forestry, Ministry for
Food, Agriculture, Forestry and Fisheries, Republic of
Korea.
REFERENCES
[1] E. Polat, M. Karaca, H. Demir and N. Onus, “Use of
Natural Zeolite (Clinoptilolite) in Agriculture,” Journal of
Fruit and Ornamental Plant Research, Vol. 12, 2004, pp.
183-189.
[2] D. W. Ming and F. A. Mumpton, “Zeolites in Soils,” In: J.
B. Dixon and S. B. Weed, Eds., Minerals in Soil Environ-
ments, 2nd Edition, Soil Science Society of America, Ma-
dison, 1989, pp. 874-911.
[3] A. K. Bansiwa, S. S. Rayalu, N. K. Labhasetwar, A. A.
Juwarkar and S. Devotta, “Surfactant-Modified Zeolite as
a Slow Release Fertilizer for Phosphorus,” Journal of Ag-
ricultural and Food Chemistry, Vol. 54, No. 13, 2006, pp.
4773-4779.
[4] T. S. Perrin, D. T. Drost, J. L. Boettinger and J. M. Nor-
ton, “Ammonium-Loaded Clinoptilolite: A Slow-Release
Nitrogen Fertilizer for Sweet Corn,” Journal of Plant Nu-
trition, Vol. 21, No. 3, 1998, pp. 515-530.

Effect of Ammonium- and Potassium-Loaded Zeolite on Kale (Brassica alboglabra) Growth and Soil Property 1982
http://dx.doi.org/10.1080/01904169809365421
[5] E. Lichtenberg and L. S. Shapiro, “Agriculture and Ni-
trate Concentrations in Maryland Community Water Sys-
tem Wells,” Journal of Environmental Quality, Vol. 26,
No. 1, 1997, pp. 145-153.
[6] T. S. Perrin, D. T. Drost, J. L. Boettinger and J. M. Nor-
ton, “Ammonium-Loaded Clinoptilolite: A Slow-Release
Nitrogen Fertilizer for Sweet Corn,” Journal of Plant Nu-
trition, Vol. 21, No. 3, 2008, pp. 515-530.
[7] S. W. Ritchie, J. J. Hanway and G. O. Benson, “How a
Corn Plant Develops,” Iowa State University of Science
and Technology Cooperative Extension Service, Special
Report, 1997.
[8] J. M. Bremner and C. S. Mulvaney, “Nitrogen-Total,” In:
A. L. Page, R. H. Miller and D. R. Keeney, Eds., Part 2.
Methods of Soil Analysis, Agronomy 9, American Society
of Agronomy, 1982, pp. 403-430.
[9] NIAST, “Methods of Soil Chemical Analysis, National
Institute of Agricultural Science and Technology,” RDA,
Suwon, 2000.
[10] Y. Watanabe, F. Uchiyama and K. Yoshida, “Compositio-
nal Changes in Spinach (Spinacia oleracea L.) Grown in
the Summer and in the Fall,” Journal of Japanese Society
of Horticulture, Science, Vol. 62, 1994, pp. 889-895.
[11] K. Torri, “Utilization of Natureal Zeolite in Japan,” In: L.
B. Sand and F. A. Mumpton, Eds., Natural zeolites: Oc-
currence, Properties, Use, Pergamon, Elmsford, 1978, pp.
441-450.
[12] M. D. Lewis, F. D. Moore and K. L. Goldsberry, “Am-
monium-Exchanged Clinoptilolite and Granulated Clino-
ptilolite with Urea as Nitrogen Fertilizers,” In: W. G.
Pond and F. A. Mumpton, Eds., Zeo-Agriculture: Use of
Natural Zeolites in Agriculture and Aquaculture. West-
view Press, Boulder, 1984, pp. 105-111.
[13] D. W. Ming and J. L. Boettinger, “Zeolites in Soil Envi-
ronments,” Reviews in Mineralogy and Geochemistry,
Vol. 45, No. 1, 2001, pp. 323-345.
http://dx.doi.org/10.2138/rmg.2001.45.11
[14] M. Amon, M. Dobeic, R. W. Sneath, V. R. Philips, T. H.
Mis-selbrook and B. E. Pain, “A Farm-Scale Study on the
Use of Clinoptilolite Zeolite and De-Odorase for Reduc-
ing Odor and Ammonia Emissions from Broiler Houses,”
Bioresearches Technology, Vol. 61, 1997, pp. 229-237.
[15] D. R. Hershey, J. L. Paul and R. M. Carlson, “Evaluation
of Potassium-Enriched Clinoptilolite as a Potassium Source
for Potting Media,” Horticultural Science, Vol. 15, 1980,
pp. 87-89.
[16] D. W. Ming, D. J. Barta, D. C. Golden, C. Galindo and D.
L. Henninger, “Zeoponic Plant-Growth Substrates for Space
Applications,” In: D. W. Ming and F. A. Mumpton, Eds.,
Natural Zeolites: Occurrences, Properties, Use, Interna-
tional Committee on Natural Zeolites, Brockport, 1995,
pp. 505-513.