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Agriculture & Forestry, Vol. 64 Issue 3: 15-29, 2018, Podgorica
15
DOI: 10.17707/AgricultForest.64.3.02
Vesna MARKOSKA, Velibor SPALEVIC and Rubin GULABOSKI 1
A RESEARCH ON THE INFLUENCE OF POROSITY ON PERLITE
SUBSTRATE AND ITS INTERACTION ON POROSITY OF TWO TYPES
OF SOIL AND PEAT SUBSTRATE
SUMMARY
Perlite is a generic name for an amorphous volcanic rock that expands by a
factor of 4–20 when rapidly heated to (760–1100°C). Water trapped in the
structure of the material vaporises and escapes, and this causes the expansion of
the material to 7–16 times its original volume. The expanded material is a
brilliant white, due to the reflectivity of the trapped bubbles. Expanded perlite
has several attractive physical properties for commercial applications, including,
low bulk density, low thermal conductivity, high heat resistance, low sound
transmission, high surface area, and chemical inertness.
The perlite supplies the ideal balance between air and water. Perlite is
sterile, inert, non-toxic, non-decomposable and easy to handle with, enhanced
water retention and aeration capacity. The application of substrates which
improve the properties of the soils requires knowledge of their physical and
chemical characteristics that are responsible for providing adequate support and a
reservoir for air, water and nutrients.
Agricultural production is increasingly concerned about the study of the
impact of improvers of properties, such as perlite, that affect the properties of
soils as well as their impact on yield and plant quality. The goal of this paper is to
observe the influence of porosity on the Perlite substrate and its interaction with
the porosity of two types of soil and the peat substrate. The laboratory part
comprised preparation of the substrate perlite, soils, and substrate peat for
analyses and conducting quantitative laboratory analysis.
The substrate perlite, soils and substrate peat were analysed in all five of
their different ratios: Perlite (Pe) 20%; 30%; 50%; 70%; 80% by volume) and
100% perlite. Fluvial soil (FS) 80%; 70%; 50%; 30%; 20% by volume) and
100% fluvial soil. Mollic Vertic Gleysol (GS) 80%; 70%; 50%; 30%; 20% by
volume) and 100% mollic vertic gleysol. Peat (P) 80%; 70%; 50%; 30%; 20% by
volume) and 100% Peat. In laboratory conditions the total porosity (in percentage
form) was determined with the help of apparent and specific density (apparent
density through applying the Koppecki method (specific density was determined
1Vesna Markoska (corresponding author: vesnemarkoska@yahoo.com), Faculty of Environmental
Resources Management, MIT University, Skopje, Republic of MACEDONIA. Velibor Spalevic,
University of Montenegro, Faculty of Philosophy Niksic, Department of Geography,
MONTENEGRO; Rubin Gulaboski, Faculty of Agriculture, Faculty of Medical Sciences,
University "Goce Delcev" Stip, Republic of MACEDONIA;
Notes: The authors declare that they have no conflicts of interest. Authorship Form signed online.
Markoska et al.
16
through the Gracanin method. The pores’ total content is determined indirectly
on the basis of the specific mass and volume mass. The results will be displayed
through statistical data processing.
Key words: perlite, soil, porosity.
INTRODUCTION
Perlite is a 100% natural siliceous volcanic glass mineral, which traps
crystalline water into its mass. Perlite expands when rapidly heated in
temperatures of 700°C–1100°C (Dogan and Alkan, 2004). The way of
preparation of fine expanded perlite, was given by (Sodeyama et al., 1999).
Causing entrapped water molecules in the rock to turn to steam and expand the
particles like popcorn.
The abrupt, controlled rise of temperature forms a white mass of
minuscule glass bubbles. Perlite melts and expands in an extremely porous
surface and increasing its volume up to 4-20 times of its original volume (Ennis,
2011). It is very porous, has a strong capillary action and can hold 3–4 times its
weight in water. (Bures et al. 1997a). This microstructure gives the material a set
of favourable properties such as excellent insulation properties, low density and
high porosity (Sengul et al., 2011; Kramar and Bindiganavile 2013; Polat et al.,
2015). Here are a number of obvious advantages of perlite over other substrates
like stability, great properties such as: ultra-lightweight, excellent water retention
up to four times its weight, advances drainage and aeration, pH natural and
asbestos free, chemically inert, sterile, free of weeds and permanent, serves as an
insulator to reduce extreme soil temperature fluctuations, reduces concentrations
of salt and also promotes the long term effect of fertilizers (Raviv, M., and Lieth,
J ,H, 2008; Asher B.,T et al., 2008).
Moreover, it is commonly used in the food industry, filter product,
growing of seed, regulating of the soil in agriculture, and in so many other
industrial applications (Alihosseini et al., 2010). Perlite has very good physical
characteristics. The physical properties of container-growing substrates,
particularly air space, container capacity, and bulk density, have a significant
impact on plant growth, and knowledge of these properties is essential in
properly managing nursery irrigation and fertilization programs (Yeager et al.,
2000). Peat is formed as a result of the partial decomposition of plants
(Sphagnum, Carex) typical of poorly drained areas (peat bogs), with low
nutrients and pH, under low temperatures and anaerobic conditions (Raviv et al.,
2002). Other relevant properties are the high easily available water under
conditions of container capacity, i.e. after the end of free drainage and the high
oxygen diffusion rate. On the other hand, as negative aspect peat can be a
conducive substrate for numerous soil-borne diseases and its sterilization does
not solve the problem as it leaves a biological vacuum that can be easily filled by
pathogenic fungi. (Abad et al., 2001).
Peat use in horticulture increased during the last decades, resulting in
rising costs and generating doubts about availability of this material in the near
A research on the influence of porosity on perlite substrate and its interaction on porosity...
17
future due to environmental constraints. In fact, peat mining has been recently
questioned because it is harvested from peat lands, highly fragile wetlands
ecosystems with a great ecological and archaeological value, included in the list
of natural habitats with a potential degradation. (Barber et al., 1993). Peat also
plays an important role in improving groundwater quality, and peat bogs also
serve as a special habitat for wild plants and animals. Moreover, these
ecosystems represent important carbon dioxide (CO2) sinks (Maher et al., 2008).
Peat is the most widely used growing media and substrate component in
horticulture, currently accounting for 77–80 percent of the growing media used
annually in Europe’s horticultural industry (Gruda, 2012),
Seedlings and transplants are grown predominantly in organic substrates
based on peat it is also used in horticulture as a raw material for substrates in
which container plants are grown (Gruda, 2005). The term alluvial originates
from the Latin word alluvio which means rubble. Lately, names that originate
from the Latin word fluvius river are being used. The following such names can
be frequently encountered: fluviogenic soil, fluvizem, fluvisol, fluvent etc. In our
newest classification multiple terms are used: alluvial or fluviatile soils (fluvisol)
which are classified as fluvisol according to WRB 2016. In regards to physical
properties fluvial soils are quite heterogeneous in their mechanical composition.
All varieties of soils can appear among fluvial soils from sandy to clayish soils.
However, they are most often sandy loam or loamy sand. In most cases, fluvial
soils have good porosity, an advantageous relation between capillary and non –
capillary pores, they are well aerated, they permeate water quite well etc.
The following definition is ascribed for the soil type of Mollic Vertic
Gleysol (Filipovski, 1996) hydromorphic soils which have a darkly colored
mollic humus horizon with possible signs of hydromorphy. The humus horizon
usually has a dark grey color to a distinctly black color, out of which the name is
derived. These soils are rich in clay and the clay content is above 40% in hor. A.
The physical properties (water-air regime) of these soils depend on the
mechanical composition of the substrate and the mineralogical composition
(especially the contents of montmorillonite), the humus contents, some processes
that are significant for the physical properties (re-covering with new rubble,
duality of the layers, alkalization and human influence).
Aeration as an important physical property is of great significance for non
– capillary porosity which on average is around 5%. This speaks to the fact that
the soil is not aerated enough when it is saturated in regard to its field capacity.
The goal of this paper is to observe the influence of porosity on the perlite
substrate and its interaction with the porosity of two types of soil and the peat
substrate. The water and air regime of the soil/substrate depends on the porosity
and its character which means supplying the plant with sufficient quantities of
water and air. Knowing the total porosity, the relationship between the
macropores and micropores, the stability of the porous system and the total
internal surface of the pores has an immense practical significance for the soil as
well as the substrates for plants growth.
Markoska et al.
18
MATERIAL AND METHODS
The experimental part served to determine on the influence of porosity on
perlite substrate and its interaction on porosity of two types of soil and peat
substrate. The experimental part was divided into two parts: field part and
laboratory part. The used perlite originates from Cera Poliana, Mariovo
Gradesnica, Republic of Macedonia, and was applied in expanded (commercial)
form. The experimental part was divided into two parts: field part and laboratory
part. The laboratory part comprised preparation of the substrate perlite, soils, and
substrate peat for analyses and conducting quantitative laboratory analysis.
The substrate perlite, soils and substrate peat were analyzed in all five of
their different ratios: Perlite (Pe) 20%; 30%; 50%; 70%; 80% by volume) and
100% perlite, Fluvial soil (FS) 80%; 70%; 50%; 30%; 20% by volume) and
100% fluvial soil. Mollic Vertic Gleysol (GS) 80%, 70%, 50%; 30; 20 by
volume) and 100% mollic vertic gleysol. Peat (P) 80%; 70%, 50%; 30%; 20% by
volume) and 100% peat. The soil samples were taken at depth of 0-30cm. In
laboratory conditions, soil samples were brought to an airy dry state. Then the
soil was finely milled and sifted through a sieve with 2mm openings, and an
average analytical sample was prepared in which further soil analysis was carried
out. In laboratory conditions the total porosity (in percentage form) was
determined with the help of apparent and specific density (apparent density
through applying the Koppecki method (Mitrikeski and Mitkova, 2013) (specific
density was determined through the Gracanin method (Resulovic, H. et al.,
1971). The pores’ total content is determined indirectly on the basis of the
specific mass and volume mass.
The results will be displayed through statistical data processing. The first
statistical analysis of the gathered data was made with the descriptive procedure
for analysis of frequencies and data dispersion depending on the factors of
influences. The obtained results are represented as an average with a ± standard
deviation from the arithmetic mean value. With the help of the general linear
model, the multivariate procedure, the influence of independent (factor) variables
were tested and their interaction on the mean values of the different groupings
from the physical and chemical properties of the examined variants. For those
variables, for which the F-value has displayed statistical significance, a post –
hoc test was implemented i.e the Bonferoni test. With it, the differences between
the specific mean values of the pairs were assessed in a multiple comparison for
the factors involved in the model. The interdependence of variables incorporated
in statistical regression models was examined through Pearson’s correlation
coefficient. The obtained results will be presented through tables, sketches, etc.
RESULTS
In Table 1 the results are displayed with the mean values of: total porosity,
water and air porosity of the analyzed samples: Perlite (Pe) 20%; 30%; 50%;
70%; 80% by volume) and 100% perlite. Fluvial soil (FS) 80%; 70%; 50%; 30%;
20% by volume) and 100% fluvial soil. Mollic Vertic Gleysol (GS) 80%; 70%,
A research on the influence of porosity on perlite substrate and its interaction on porosity...
19
50%; 30%; 20% by volume) and 100% Mollic Vertic Gleysol. Peat (P) 80%;
70%; 50%; 30%; 20% by volume) and 100% peat. The results of the multivariate
regression statistical model will be presented for the influence of the different
variants, the different correlation in variants and their interaction with total
porosity, water and air porosity. Additionally, the results of the post hoc analysis
for the testing of the differences in mean values of dependent variables are
presented, depending on the sources of variation.
The analyzed sample of Perlite (Pe) has displayed the highest percentage
of total porosity out of all analyzed samples from Table 1 with a mean value of
88.09%, out of which 60.2% in mean value is air porosity and 27.9% is water
porosity. The contents of total porosity of fluvial soil (FS) is has a mean value of
77.73% out of which 39.68% with a mean value is water porosity and 38.05% is
air porosity. All the other analysed samples in their various ratios are displayed in
Table 1.
Formulation
Designation
1.
100% Perlite (commercial
substrate)
(Pe)
2.
100% Peat (commercial
substrate)
(P)
3.
80% Perlite + 20%Peat
Pe80/P20
4.
70%Perlite + 30% Peat
Pe70/P30
5.
50%Perlite + 50% Peat
Pe50/P50
6.
30%Perlite + 70% Peat
Pe30/P70
7.
20%Perlite + 80% Peat
Pe20/P80
Formulation
Designation
1.
100% Perlite
(commercial substrate)
(Pe)
2.
100% Fluvial soil (soil)
(FS)
3.
80% Perlite + 20% Soil
Pe80/FS20
4.
70%Perlite + 30% Soil
Pe70/FS30
5.
50%Perlite + 50% Soil
Pe50/FS50
6.
30%Perlite + 70% Soil
Pe30/FS70
7.
20%Perlite + 80% Soil
Pe20/FS80
Formulation
Designation
1.
100% Perlite (commercial
substrate)
(Pe)
2.
100% Mollic Vertic Gleysol
(Soil)
(GS)
3.
80% Perlite + 20% Soil
Pe80/GS20
4.
70%Perlite + 30% Soil
Pe70/GS30
5.
50%Perlite + 50% Soil
Pe50/GS50
6.
30%Perlite + 70% Soil
Pe30/GS70
7.
20%Perlite + 80% Soil
Pe20/GS80
Table 1. Physical properties of perlite substrate and fluvial soil
n
Air porosity %
Water porosity %
Total porosity %
x
SD
x
SD
x
SD
Pe-Perlite
3
60.20
0.01
27.90
0.01
88.09
0.01
FS-Fluviol Soil
3
38.05
0.28
39.68
0.60
77.73
0.84
Pe80/FS20
3
55.77
0.01
29.61
0.01
85.38
0.01
Pe70/FS30
3
53.56
0.19
31.43
0.40
84.99
0.23
Pe50/FS50
3
49.13
0.03
33.79
0.03
82.92
0.02
Pe30/FS70
3
44.69
0.62
36.15
0.22
80.84
0.79
Pe20/FS80
3
42.48
1.06
37.16
0.89
79.64
1.95
Markoska et al.
20
An overview of the following results is displayed in Table 2 total porosity,
water and air porosity of analyzed samples of Perlite (Pe), Mollic Vertic Gleysol
(GS) and their mixtures in various ratios. The highest value of total porosity was
recorded in the Perlite ratio with a mean value of 88.09% while the lowest value
was recorded in the Mollic Vertic Gleysol with a mean value of 49.99%. The
highest percentage of water porosity was noted in the mollic vertic gleysol with a
mean value of 42.79% and the lowest in perlite with a mean value of 27.9%.
The highest air porosity was noted in perlite with a mean value of 60.2%
while the lowest air porosity was recorded in mollic vertic gleysol with a mean
value of 4.21%. All the other analyzed samples in their various ratios are
displayed in Table 2
Table 2. Physical properties of perlite substrate and mollic vertic gleysol
n
Air porosity
%
Water porosity
%
Total porosity
%
x
SD
x
SD
x
SD
Pe-Perlite
3
60.20
0.01
27.90
0.01
88.09
0.01
GS- Mollic vertic gleysol
3
4.21
1.41
42.79
0.01
46.99
1.41
Pe80/GS20
3
49.00
2.74
30.23
1.06
79.23
0.86
Pe70/GS30
3
43.40
1.70
32.37
1.03
75.77
0.93
Pe50/GS50
3
32.20
1.03
35.34
1.17
67.54
1.65
Pe30/GS70
3
21.00
0.09
38.23
0.93
59.23
1.33
Pe20/GS80
3
15.40
0.92
39.65
1.22
55.05
1.13
The following results are displayed in Table 3 total porosity, water and air
porosity and the total retention capacity of the analyzed samples of Perlite, Peat
and their mixtures in various ratios. The highest total porosity was noted in Peat
(P) with 90.8% out of which 10.7% belong to air porosity and 80.1% with a mean
value belong to water porosity. A somewhat lower porosity was noted in Perlite
(Pe) with a mean value of 88.09% out of which 27.9% belong to water porosity
and 60.2% to air porosity. All the other analyzed samples in their various ratios
are displayed in Table 3.
Table 3. Physical properties of Perlite substrate and peat
n
Air porosity %
Water porosity %
Total porosity %
x
SD
x
SD
x
SD
Pe-Perlite
3
60.20
0.01
27.90
0,01
88.09
0.01
P-Peat
3
10.70
1.03
80.10
0.93
90.80
1.95
Pe80/P20
3
50.30
0.16
39.96
0.53
90.26
0.68
Pe70/P30
3
45.35
0.15
44.64
1.08
89.99
1.02
Pe50/P50
3
35.45
0.28
54.00
0.28
89.45
0.55
Pe30/P70
3
25.55
0.56
63.55
0.41
88.90
1.76
Pe20/P80
3
20.60
0.83
68.03
0.60
88.63
1.58
A research on the influence of porosity on perlite substrate and its interaction on porosity...
21
Table 4. Multivariate general linear model for the influence of variants, various
ratios within the variants and their interaction on water porosity, air porosity,
total porosity
Parameters
Source of variation
Model
Variants
Ratios
Variants x ratios
Error
df
F
df
F
df
F
df
F
df
Variance
aAir porosity
%
21
5454
.2*** 2 1045.4***
6 1919.9
***
12 1360.8
***
42 0.9
bWater
porosity %
21
7046
.9*** 2 6245.3***
6 836.6
***
12 1163.3
***
42 0.9
cTotal porosity
%
21 14120.
7***
2 3608.3***
6 335.8
***
12 138.3
***
42 1.2
aR2 = 0,919; bR2 = 1; cR2 = 0,1.
***statistically significant on level p<0.001;**statistically significant on level p<0.01;*statistically significant
on level p<0.05
All statistical models about the influence of the variants and the different
ratio of Perlite and fluvial soil, Perlite and Peat and Perlite with Mollic Vertic
Gleysol soil in the respective variants, as well as the interaction of the variant and
the ratio with water porosity, air porosity and total porosity have displayed a high
statistical significance (p<0.001).
According to the results obtained out of the statistical model, displayed in
Table 4 the variants displayed a significant statistically high influence of water
porosity, air porosity and total porosity (p<0.001). The influence of the various
ratios within the variants have also displayed a significant statistically high
influence on water porosity, air porosity and total porosity (p<0.001). The
interaction of the variants and the ratios have displayed a statistically high
influence (p<0.001) on water porosity, air porosity and total porosity. The value
of R² in all three statistical models was high. This means that a large part of the
variant for water porosity, air porosity and total porosity can be explained
through the variation sources involved in the model.
The testing of the differences between the mean values of air porosity
depending on the variant are displayed in Table 5. A statistically significant
difference between the mean values of air porosity was recorded among all
variants. Throughout it, the largest statistically significant difference in the mean
values of air porosity has been determined among the Perlite/Fluvial soil and
Perlite/Peat variants with a value of 12.72%.
Table 5. Testing the differences of the mean values of air porosity between the
variants
Air porosity %
Perlite/ Peat
Perlite/ Mollic Vertic Gleysol
Perlite/ Fluvial soil
12.72*
9.1*
Perlite/ Peat
1
-3.6*
*statistically significant on level p<0.05
Markoska et al.
22
Table 6. Testing the differences of the mean values of air porosity depending on
the different ratio of Perlite, Fluvial soil, Peat and Mollic Vertic Gleysol in the
respective variants
Air porosity %
FS,GS,
P70/Pe30
FS,GS,P80/
Pe20
FS,GS,
P30/Pe70
FS,GS,
P20/Pe80
Perli
te
FS, FG, P
FS,GS,P50/Pe50
6.49*
9.58*
-2.27*
-5.67*
-31.11*
-11.70*
FS,GS,P70/Pe30
1
3.10*
-8.75*
-12.15*
-37.60*
-18.19*
FS,GS,P80/Pe20
1
-11.85*
-15.25*
-40.70*
-21.28*
FS,GS,P30/Pe70
1
-3.40*
-28.85*
-9.43*
FS,GS,P20/Pe80
1
-25.45*
-6.03*
Perlite
1
19,41*
*statistically significant on level p<0.05
A statistically significant negative difference was noted in the mean values
of air porosity between Perlite and the different ratios which points to the
realization that the percentage of air porosity in Perlite is larger compared to the
presence of air porosity in the different ratios of the variants in Table 6. The
biggest statistically significant difference between the values of air porosity of
the variants was determined between the ratio FS, GS, P80/Pe20 and FS, GS,
P20/Pe80 with a value of 15.25%. Likewise, the difference in the mean values of
air porosity of the soils and Peat that are used in the formation of various ratios
and the ratios within the variants has displayed a statistically significant
difference. However, the greatest difference in the mean values of air porosity i.e.
19.41% was noted between Perlite and the appropriate soils and Peat which in
various ratios comprised the variants.
The testing of the differences between the mean values of water porosity
depending on the variant is displayed in Table 7. A statistically significant
difference between the mean values of water porosity was noted among all
variants. Throughout it, the largest statistically significant difference in the mean
values of water porosity was determined between the variants Perlite/Mollic
Vertic Gleysol and Perlite/Peat with a value of 30.94%. A very noticeable fact
was the statistically significant positive difference in the mean values of water
porosity between Perlite and the ratio FS, GS, P80/Pe20. The largest statistically
significant difference between the values of water porosity and the variants was
determined between the ratio FS, GS, P80/Pe20 and FS, GS, P20/Pe80 with a
value of 15.98%.
Table 7. Testing the differences of the mean values of water porosity between the
variants
Water porosity %
Perlite/Peat
Perlite / Mollic Vertic Gleysol
Perlite/ fluvial soil
-20.08*
10.86*
Perlite/Peat
1
30.94*
*statistically significant on level p<0.05
A research on the influence of porosity on perlite substrate and its interaction on porosity...
23
Table 8. Testing the differences of the mean values of water porosity depending
on the different Perlite ratio, Fluvial soil, Peat and Mollic Vertic Gleysol in the
respective variants
Water porosity
%
FS,GS
,P70/Pe30
FS,GS
P80/Pe20
FS,GS
P30/Pe70
FS,GS
P20/Pe80
Perlite
FS,GS,P
FS,GS,P50/Pe50
-5.70*
-8.81*
5.85*
7.17*
14.82*
11.66*
FS,GS,P70/Pe30
1
-3.11*
11.55*
12.87*
20.52*
17.36*
FS,GS,P80/Pe20
1
14.66*
15.98*
23.63*
20.47*
FS,GS,P30/Pe70
1
1.32
8.97*
5.81*
FS,GS,P20/Pe80
1
7.65*
4.49*
Perlite
1
-3.16*
*statistically significant on level p<0.05
The difference in the mean values of water porosity of the soils and Peat
used in the formation of the various ratios and the ratios within the variants has
also indicated a statistically significant difference depicted in Table 8. However,
the largest difference in the mean values of water porosity i.e. 20.47% has been
noted between Perlite and the respective soils and Peat which in various ratios
formed the variants. The testing of the differences between the mean values of
total porosity depending on the variant is displayed in Table 9. A statistically
significant difference between the mean values of total porosity was noted among
all variants. Throughout it, the largest statistically significant difference in the
mean values of total porosity was determined among the Perlite/ Mollic Vertic
Gleysol and Perlite/Peat variants with a value of 27.63%.
Table 9. Testing the differences of the mean values of water porosity between
variants
Total porosity %
Perlite/Peat
Perlite / Mollic Vertic Gleysol
Perlite/ fluvial soil
-7.63*
19.99*
Perlite/Peat
1
27.63*
*statistically significant on level p<0.05
Table 10. Testing the differences of the mean values of total porosity depending
on the different ratio of Perlite, Fluvial soil, Peat and Mollic Vertic Gleysol in the
respective variants
Total porosity
%
FS,GS
P70/Pe30
FS,GS
P80/Pe20
FS,GS
P30/Pe70
FS,GS
P20/Pe80
Perlite
FS, GS, P
FS,GS,P50/Pe50
0.34
0.55
3.54*
1.50
-16.29*
-0.04
FS,GS,P70/Pe30
1
0.21
3.20*
1.17
-16.63*
-0.38
FS,GS,P80/Pe20
1
2.99*
0.95
-16.84*
-0.59
FS,GS,P30/Pe70
1
-2.04*
-19.83*
-3.58*
FS,GS,P20/Pe80
1
-17.79*
-1.5
Perlite
1
16.25*
*statistically significant on level p<0.05
A statistically significant negative difference was once more noticeable in
the mean values of total porosity between Perlite and the different ratios which
Markoska et al.
24
points to the realization that the total porosity in Perlite is larger compared to the
total porosity in the various ratios of the variants. The largest statistically
significant difference between the values of total porosity was determined
between the ratio FS, GS, P30/Pe70 and FS, GS, P50/Pe50 with a value of 3.54%
which is depicted in Table 10. The difference in the mean values of total porosity
of the soils and Peat used in the formation of different ratios and the variants
ratios has also displayed a statistically significant difference. Never the less, the
largest difference in the mean values of total porosity i.e. 16.25% was noted
among Perlite and the respective soils and Peat which comprised the variants in
various ratios.
DISCUSSION
Porosity or void fraction is the total volume of the pores (cavities)
expressed in voluminous percentages of the total soil/raw material in a natural
(undistorted) state. The volume of all pores in a certain volume i.e. soil/raw
material constitutes total porosity which is encompassed by water and air. In the
macropores (non – capillary pores) there is air while in the micropores (capillary
pores) there is water. Through irrigation the water gets into all pores but it is only
retained in the capillary pores. A different ratio between capillary and non –
capillary pores will induce a different water and air regime. Total porosity,
capillary and non – capillary porosity differ among each other. In our research
the values of total porosity, water porous capacity, air porous capacity of Perlite
substrate with Fluvial soil, Mollic Vertic Gleysol and Peat substrate were
analyzed. Out of the obtained results with their respective values from Table 1
and Table 2 for total porosity it can be noted that Perlite as a substrate has a very
high porosity with a mean value of 88.09% out of which 60.2% belong to air
porosity and 27.9% belong to water porosity with high capillary porosity. This is
due to the high porosity level which facilitates the retention of oxygen and water
in the pores.
The effortless availability of nutrients and water is of great significance for
the healthy growth and development of plants. (De Boodt and Verdonck, 1972)
and (Fonteno et al, 1981) through their research point to the fact that an ideal
substrate should have a TPS or total porous space which exceeds 85%. The pores
are filled with air or water depending on their dimension and the contents of the
base. The substrates’ total porous space is higher than the soils’ porous space
whose percentage amounts to a quantity which is approximately 50% of the
volume. (Michiels et al., 1993) claims in his research that in principle, according
to the shape and size of the particles, organic substrates should have a total
porosity that amounts to around 85-95% of the volume (Michiels et al., 1993;
Raviv at al., 2002) in his research points to the fact that the total porous space in
the substrates for plant cultivation should amount to 60-90% in volume. A lot of
studies and authors with (Eriksson, 1982) being one of them stressed the
importance of the presence of air in the pores for healthy growth of plants and
high yield.
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25
The authors (Wesseling and Van Wijik, 1957; Paul and Lee, 1976) stress
that there is a general consensus on the fact that the minimal volume of the air
porous space for an appropriate air exchange for supporting plant growth should
amount to around 10% of the volume. (Brückner U, 1997) underscores in his
research that the relative balance of air and water in the pores of the soil space is
of crucial significance for the growth of plants.
The analyzed soil sample of fluvial soil in Table 1 also has a high total
porosity with a mean value of 77.73% which points to the fact that this type of
soil falls in the category of soils which are high in porosity which is an indicator
for excellently aeriated soils rich in sand and with less clay which influence high
porosity. (Filipovski, 1997) has divided soil types depending on porosity in four
categories: quite porous (pores that exceed 60%), porous (45-60%), slightly
porous (30-45%) and quite moderately porous (pores whose percentage is below
30%).
Knowing the value of total porosity, the relation between macropores and
micropores, the porous system’s stability and the total internal surface of the
pores has immense practical significance for the soil and the growth of plants. It
is not beneficial for the plant when only non - capillary or only capillary pores
are present in the soil. In the first case the soil doesn’t retain water and in the
second all the pores fill with water and enough air isn’t available or there is weak
aeration. The obtained values from the air porous space of the fluvial soil has a
mean value of 38.05% while the water porous space has a mean value of 39.68%
which can be explained with the fact that fluvial soil has an optimal water and air
regime. (Gajic, 2006) points to the fact that optimal physical and water physical
properties and their water – air regime can be obtained when the capillary and
non – capillary porosity are in a mutual relation of 1:1 or 2:3. (Filipovski, 1996)
claims that the most advantageous relation of porosity occurs when out of the
total porosity 60% of the pores are capillary pores and 40% of the pores are non –
capillary pores. All the other analyzed samples have displayed optimal water –
air porosity.
Out of the analyzed properties of the Mollic Vertic Gleysol soil type and
Perlite substrate with their mixtures in Table 2 we can draw the conclusion that
the examined trials of total porosity of Mollic Vertic Gleysol have displayed a
total porosity with a mean value of 46.99% which points to a soil which is
porous. But, the Mollic Vertic Gleysol soil type falls in the category of clay soils
with high porosity. Its characteristics are low presence of non – capillary pores
with a presence which usually doesn’t exceed 8% which makes the water – air
regime of these soils disadvantageous. In our research the obtained values from
the analyzed properties of water porosity had a mean value of 42.79% and a high
capacity of the capillary pores while the analyzed samples of air porosity
displayed quite low values with a result of 4.21%. This is due to the high
percentage of clay present in that soil, the low presence of non – capillary pores,
poor filtration and infiltration with the low diffusion of gasses which characterize
poorly aerated soil. The authors (Steffens D, et al., 2005) point to the fact that
Markoska et al.
26
soils which access to limited conditions for aeration in the inside of the soil’s
porous volume have an increase in CO2concentration with a transient increase of
pH around the root’s absorption system. The author (Spirovski, 1965) achieved
similarly low values of air porosity in his research with a value of 6.44%.
Because of the higher content of clay, Mollic Vertic Gleysol is falls into the
category of heavy soils in which non – capillary pores dominate while clay soils
despite the greater content of capillary pores often have a low quantity of easily
accessible water because of the high content of micropores (smaller than 3
microns). The water in these micropores isn’t easily accessible for the plants. Out
of the results in Table 3 it can be easily noted that out of the analyzed properties
of Peat substrate the highest result for total porosity stands out with a mean value
of 90.8% which defines a high total porous volume. This high percentage of
porosity present in Peat is due to the high content of organic matter which can be
found in Peat.
With the increase of organic matter the total porosity also increases. Never
the less, the mutual water and air regime is disadvantageous because the capillary
pores have a mean value of 80.1% which points to a very high content of water
capacity while air capacity has a low capillarity or insufficient retention of air
with a mean value of 10.7%. All the other analyzed samples in various ratios
indicate a different balance between the water and air regime. With adding or
mixing of Perlite and Peat, the percentage of air porosity increases. For example,
the analyzed sample in a mixture with a ratio Pe20/P80 or 20% Perlite + 80%
Peat displays a total porosity with a mean value of 88.63%, which points to high
porosity and an advantageous water – air regime. Air capacity has a mean value
of 20.6% and water porosity has a high mean value of 68.03%. All the other
analyzed samples of mixtures in ratios of Pe50/P50 and Pe70/P30 display
different values. By adding a mixture of 50% Perlite and 50% Peat total porosity
reaches a mean value of 89.45%, air porosity reaches a mean value of 35.45%
while water porosity displays a mean value of 54.0%. These states allow us to
claim that the analyzed sample Pe50/P50 has a high total porosity and
advantageous water – air capacity. By adding a mixture of 30% Perlite and 70%
Peat the total volume of the pores (both capillary and non – capillary) reaches a
value of 88.9%.
The water regime is high and filled with capillary pores with a mean value
of 63.55%. Non – capillary pores have an advantageous air porosity with a mean
value of 25.55%. Similar results to ours were also obtained by the authors (Jeb S,
Fields et al., 2014) in their research on the hydrohpysical properties of Perlite and
Peat. They reached the following results: total porosity of Peat with a value of
91.0%, air porosity with a value of 10.7%, water porosity of Perlite with a value
of 66.4% and air porosity with a value of 12.2%.
CONCLUSIONS
Once more, the analyzed properties of total porosity of Perlite as a
substrate have displayed a very high porosity with a mean value of 88.09% out of
which 27.9% belong to water porosity which points to a presence of solid
A research on the influence of porosity on perlite substrate and its interaction on porosity...
27
capillary porosity while the researched properties of air porosity in Perlite have
displayed a very high air capacity with a mean value of 60.2%. That points to the
fact that this is a substrate with a high level of superiority for appropriate
retention of air whose application can act as a betterment for the increase of
aeration of problematic heavy soils which will impact plants directly in their
roots when the need for stable supply with oxygen exists. Through the
application of Perlite in mixtures in various ratios an influence of the water and
air porosity is displayed in the analyzed samples of fluvial soil, mollic vertic
gleysol and Peat.
The fluvial soil type also has a high total porosity with a mean value of
77.73%. The obtained values from the air porous space of the fluvial soil type has
a mean value of 38.05% while the water porous space has a mean value of
39.68%. This can be explained with the high water and air porosity because of
the high quantity of sand and the lower quantity of clay. While it is a
characteristic of mollic vertic gleysol soil type to have a low percentage of non –
capillary pores with a value which doesn’t exceed 8% which points to a low
percentage of air porosity. Water porosity has an average value of 46.99% which
points to an advantageous water porosity. This soil type has a disadvantageous
ratio of water and air i.e. a weak exchange between the water regime and the
aeration regime. Here the positive influence of Perlite substrate on air porosity is
the most visible.
There is a drastic improvement of the air porosity in soil. It can be derived
out of all of this that Perlite as a substrate improves the soil’s aeration power of
soil types with a poorer aeration capacity. It can be derived out of the analyzed
properties of Peat substrate that this substrate stands out with the highest total
porosity with a mean value of 90.8% that defines a high total porous volume.
This high Porosity percentage in Peat is due to the high content of organic matter
which can be found in Peat. With the increase of organic matter itself the total
porosity increases. Nevertheless, the mutual water and air regime is
disadvantageous because capillary pores have a mean value of 80% which points
to a very high content of water capacity while air capacity has a low capillarity or
insufficient air retention with a mean value of 10.7%. In all the other ratios a
different balance between the water and air regime can be noted while with the
mixing of Perlite and Peat, air porosity displays a higher percentage.
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