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59
ORIGINAL SCIENTIFIC PAPER
Summary
Aeration of horticultural media is o en reported to be a problem. e air
lled porosity is generally considered as the quality determining factor for
media and is generally determining the shape of the moisture characteristic
curve. e objective of this study was to determine a ects of di erent size
and rate of pumice mixed with soil on the pore size distribution and bulk
density of a mixture medium. Pumice of di erent size (<4 mm, <8 mm, and
4-8 mm) and rate on volumetric basis (10, 20, 30, 40, 50 % v/v) was mixed
with two types of loamy soils passed through an 8 mm sieve. e moisture
characteristic curve and bulk density of each mixture media was determined.
From the moisture characteristic curve pore size distribution was obtained.
Aeration, water conductivity, and water retention of media were evaluated. e
results indicated that total porosity increased with increasing rate and size of
pumice. e amount of pores important for drainage and aeration increased,
but bulk density decreased signi cantly (p<0.01) with the increase in the
rates of pumice mixed with soil. At 50 % pumice application, the increase in
macropores (>100 m diameter) were 98.2 % and 70.3 %, and the decreases in
bulk density were 24.8 % and 21.0 % for soil I and II, respectively. While the
mesopores (100-30 m diameter), which are important for water conductivity,
decreased signi cantly with pumice application in soil I, no signi cant changes
were obtained for soil II. e amount of water held at 0.01 MPa – 0.10 MPa
decreased signi cantly with 30 % or more pumice application in both soils. e
amount of water held at 0.10 MPa or greater suctions decreased with pumice
application. Signi cant changes in physical properties of soil-pumice mixture
media were obtained for di erent sizes of pumice application.
Key words
bulk density; pore size distribution; soil-pumice mixture media
Agriculturae Conspectus Scienti cus, Vol. 71 (2006) No. 2 (59-64)
Addition of Pumice A ects Physical
Properties of Soil Used for Container
Grown Plants
Ustun SAHIN ( )
Omer ANAPALI
Ataturk University, Faculty of Agriculture,
Department of Agricultural Structures and Irrigation
25240, Erzurum, Turkey
e-mail: ussahin@atauni.edu.tr
Received: May 18, 2006 | Accepted: June 21, 2006
Agric. conspec. sci. Vol. 71 (2006) No. 2
60 Ustun SAHIN, Omer ANAPALI
Introduction
Soil and some soilless media are used as plant-growth
media in horticulture. Liquid fertilizers are essential for
soilless plant-growth media. In soilless cultures, con-
tinuous controlling is required for soil reaction (pH),
salinity and plant nutrient equilibrium because of low
bu ering capacities of these media. On the other hand,
although plant-growth media with soil may have sev-
eral disadvantages due to not providing desirable soil at
all times, heavy texture, and need for sterilization, plant
nutrition in soil media is easier because the nutrients are
retained by soil. In addition, minor element de ciencies
are rare because the elements are on the soil exchange
sites (Holcomb 2002).
In a medium with soil, the provision of aeration and
the improvement of drainage conditions are required.
For this reason, pumice is a good amendment for aera-
tion and drainage. Pumice mixed with soil in speci c
amounts improves soil air and water conductivity, and
reduces negative e ects of crusting, cracking, ooding,
and shrink swelling. It is also used for long periods be-
cause of its stable physical and chemical properties (Gur
et al. 1997). In general, pumice could be provided easily
since there are many pumice deposits distributed around
the world (Tuncer 1997). Pumice used only a er sieving
has a high water retention capacity, and very low bulk
density value compared to soil (Sahin et al. 2004).
e most important physical properties of a medium
for suitability are good aeration and drainage, optimum
water retention, high water conductivity and low bulk
density (Cabrera 2003). Within the physical proper-
ties, the air-water ratio is the most important (Bruckner
1997; Caron and Nkongolo 1999). e air-water ratio can
partly be determined by the granulometry and poros-
ity (Orozco et al. 1997). e relationship between water
energy status and water content of the medium is a re ec-
tion of the pore size distribution of the medium (Milks
et al. 1989). Pore sizes have traditionally been divided
into macropores, mesopores, micropores and ultrami-
cropores (Sahin et al. 2002). e macropores (>100 m
diameter) supply drainage and aeration, the mesopores
(100-30 m diameter) supply water conductivity, and
the micropores (30-3 m diameter) supply water reten-
tion (Gemalmaz 1993). e water retained in ultrami-
cropores (<3 m diameter) is unavailable for plant use
(Drzal et al. 1999).
The objective of this study was to determine the
effects of different size and rates of pumice mixed
with soil on the pore size distribution and bulk
density of the mixture medium.
Materials and methods
Two soils formed under di erent climates with 450
mm (Erzurum-Turkey) and 2200 mm (Rize-Turkey)
annual rainfalls were used. Some physical and chemical
properties of these soils and pumice are given in Table
1. e soils used in this study sampled from Ap hori-
zon (0-20 cm depth) and origin of pumice was Ercis,
Van-Turke y.
Pumice is a very light, porous igneous rock that is
formed during volcanic eruptions. It is made up of very
tiny crystals, since they cool so quickly above ground.
e texture of pumice is rough and has many hollows
and cavities. Pumice has been used to a large extent as a
plant growing media and it lightens the soil, makes tillage
easier, improves soil aeration and holds water. Pumice
mixed with soil in speci c amounts improves soil’s air
and water conductivity, and reduces negative e ects of
crusting, cracking, ooding, and shrink-swelling. It
can also be used for a long periods because of its stable
Properties Soil I Soil II Pumice
Soil taxonomy Ustent Aquoll -
Dominant clay type Montmorillonite Kaolinite -
Clay (%) 23.7 24.6 -
Silt (%) 39.8 27.7 -
Sand (%) 36.5 47.7 -
Bulk density (g cm-3) 1.05 1.00 0.65 (for < 4 mm)
0.63 (for < 8 mm)
0.40 (for 4-8 mm)
Particle density (g cm-3) 2.64 2.61 2.24
Wet Aggregate stability (%) 28.5 50.7 -
pH 8.2 6.7 8.4
Electrical cond. (dS m-1) 0.93 0.19 0.11
CEC (cmol(+) kg-1) 33.6 26.0 6.9
Carbonates (%) 2.7 0.1 0.8
Organic matter (%) 2.9 3.8 -
Table 1.
Some physical and chemical properties of soils and pumice used
Agric. conspec. sci. Vol. 71 (2006) No. 2
61
Addition of Pumice Affects Physical Properties of Soil Used for Container Grown Plants
physical and chemical properties and it can be provided
easily since there are many pumice deposits distributed
around the world. Pumice used only a er sieving has a
high water retention capacity, and very low bulk density
value compared to soil (Sahin et al. 2005).
Soil samples were passed through a sieve with open-
ings of 8 mm before mixing them with pumice. e rates
of size fractions (<2 mm, 2-4 mm, and 4-8 mm) were
58.6, 26.1 and 15.3 % for Soil I and 44.2, 29.7, and 26.1
for Soil II, respectively, following sieving.
Soil and pumice mixtures were prepared as 9:1, 8:2,
7:3, 6:4, and 5:5 ratio on volumetric basis, resulting in
10 % (M1), 20 % (M2), 30 % (M3), 40 % (M4), and 50
% (M5) of pumice in the mixture media. Similar mix-
ture media were prepared for three di erent sizes of
pumice as S1: <4 mm (50 % 2-4 mm, 25 % 1-2 mm, and
25 % < 1mm), S2: <8 mm (33.3 % 4-8 mm, 33.3 % 2-4
mm, 16.7 % 1-2 mm, and 16.7 % <1 mm), S3: 4-8 mm.
Sample with no pumice mixture was used as the con-
trol medium (C).
e soil water characteristic curve (pF curve) was
determined using pressures plates (Klute 1986), and
was used as the basis for the calculation of the pore
size distribution. Water held at 0.001 MPa, 0.01 MPa,
0.03 MPa, 0.10 Mpa and 1.5 MPa was obtained when
water output stopped for a given suction. e samples
for pF curves were packed by dropping the cylinders.
Porosity was estimated by calculation (Danielson and
Sutherland, 1986). Bulk density was determined by the
cylinder method (Blake and Hartge 1986a) on samples
packed by dropping the sample cylinders from a height
of 10 cm for 20 times.
e percentage of water-stable aggregates was deter-
mined by a wet sieving procedure (Kemper and Rosenau
1986). Particle density was determined by the pycnometer
method (Blake and Hartge 1986b), pH by a pH-meter in
saturation extract (Mc Lean 1982), Electric conductiv-
ity (EC) by an EC-meter in saturation extract (Rhoades
1982a), cation exchange capacity (CEC) by the sodium
acetate method (Rhoades 1982b), carbonates by the cal-
cimeter method (Nelson 1982) and organic matter by the
wet combustion method (Nelson and Sommers 1982).
e experimental design was factorial (soils (2),
mixture rates (5), and pumice sizes (3)) with three rep-
lications. Analysis of variance (ANOVA) for the data of
macropores, mesopores, micropores, ultramicropores
and bulk density was performed, and Duncan’s multiple
range tests were used for important treatments.
Results and Discussion
Total porosity increased with increasing rates and
sizes of pumice in both soils. e increasing rates in
total porosity were higher for Soil I than Soil II. e ini-
tial total porosity was 60.4 for Soil I and 62.1 for Soil II.
Since both soils have similar texture, it may be that the
di erences in total porosity may be related to the degree
of soil structure. erefore, pumice application to Soil
I gave better results in improving total porosity which
reached up to 12.2 % (M5) and 10.0 % (S3) as compared
to the initial porosity value.
e amount of macropores supplies aeration and
drainage increased signi cantly (p<0.01) with increas-
ing rate of pumice in the medium. Pumice mixture to
soil medium with a rate of 50 % increased the amount
of macropores by about 98.2 % in soil I and 70.3 %
in soil II compared with the control medium (Fig. 1).
Similar results were obtained in all pumice size groups.
Maximum increase was obtained for S2 treatment in
soil I, and S1 treatment in soil II (Fig. 1). e macro-
pores increased with increasing rates of pumice in the
medium in all pumice sizes. e maximum macropo-
res values were obtained in S2 treatment (Fig. 2). More
LSD =1.24
0.01
0
5
10
15
20
25
30
35
40
C 10 20 30 40 50 <4 <8 4-8
Soil I
Soil II
Rate of pumice (%v/v) Pumice size (mm)
(over means of S1, S2, and S3) (over means of M1,
M2, M3, M4, and M5)
Macroporosity (%)
LSD =0.96
0.01
1
0
5
10
15
20
25
30
35
40
10 20 30 40 50
<4mm
Rate of pumice (%v/v)
Macroporosity (%)
LSD =1.51
0.01
<8mm
4-8 mm
1
Figure 1.
Changes in macropores with pumice size and rate
Figure 2.
Changes in macropores with pumice rate in the different
pumice size
Agric. conspec. sci. Vol. 71 (2006) No. 2
62 Ustun SAHIN, Omer ANAPALI
Figure 7.
Changes in bulk density with pumice size and rate
Figure 8.
Changes in bulk density with pumice rate in the different
pumice size
Figure 3.
Changes in mesopores with pumice size and rate
Figure 4.
Changes in micropores with pumice size and rate
Figure 5.
Changes in ultramicropores with pumice size and rate
Figure 6.
Changes in ultramicropores with pumice rates in the
different pumice size
0
0,2
0,4
0,6
0,8
1
1,2
10 20 30 40 50
Bulk density(gm )
–3
<8mm
LSD =0.02
0.01
<4mm 4-8 mm
Rate of pumice (%v/v)
0
2
4
6
8
10
12
C10 20 30 40 50 <4 <8 4-8
Microporosity (%)
Rate of pumice (%v/v) Pumice size (mm)
(over means of S1, S2, and S3) (over means of M1,
M2, M3, M4, and M5)
Soil I
Soil II
LSD =1.21
0.01 LSD =0.94
0.01
1
0
1
2
3
4
5
6
7
8
C10 20 30 40 50 <4 <8 4-8
Mesoporosity (%)
Rate of pumice (%v/v) Pumice size (mm)
(over means of S1, S2, and S3) (over means of M1,
M2, M3, M4, and M5)
Soil I
Soil II
LSD =0.86
0.01 LSD =0.67
0.01
1
0
5
10
15
20
25
30
10 20 30 40 50
Rate of pumice (%v/v)
Ultramicroporosity (%)
<8mm
LSD =0.82
0.01
<4mm 4-8 mm
1
0
5
10
15
20
25
30
C 10 20 30 40 50 <4 <8 4-8
Ultramicroporosity
(
%
)
Rate of pumice (%v/v) Pumice size (mm)
(over means of S1, S2, and S3) (over means of M1,
M2, M3, M4, and M5)
Soil I
Soil IIns ns
1
1
C10 20 30 40 50 <4 <8 4-8
Rate of pumice (%v/v) Pumice size (mm)
(over means of S1, S2, and S3) (over means of M1,
M2, M3, M4, and M5)
0,5
0,6
0,7
0,8
0,9
1
1,1
Bulk density (g m )
–3
Soil I
Soil II
LSD =0.02
0.01 LSD =0.01
0.01
suitable air volume conditions were reached; due to the
macropores they were greater than 20 % in all treat-
ments (Verdonck 1984).
Pumice caused signi cant reduction of the amount
of mesopores, which e ect water conductivity, in soil
I, but no signi cant changes were determined for soil
II (Fig.3). is may be related to di erences in soil ag-
gregation (Table 1). e e ects of mixed ratio with all
pumice sizes on the amount of mesopores were not sig-
ni cant.
Agric. conspec. sci. Vol. 71 (2006) No. 2
63
Addition of Pumice Affects Physical Properties of Soil Used for Container Grown Plants
e amounts of micropores, which a ect water re-
tention, also decreased signi cantly (p<0.01) by higher
rates of pumice application. Signi cant decreases of
the amount of micropores occurred with M3-M5 treat-
ments in soil I and M4-M5 treatments in soil II. In soil
I, a small increase (8.1 %) in the amount of micropores
with M1 treatment was obtained, but it was statistically
insigni cant (Fig. 4). It means that pumice application
to soil medium in small rates has no signi cant e ect on
the amount of water retention. On the other hand, dif-
ferent sizes of pumice caused reduction in the amount of
micropores. e most signi cant reduction was obtained
with S2 treatment in soil I (25.6 %) and S1 and S2 treat-
ments in soil II (13.2 and 14.3 %, respectively) (Fig. 4).
e e ects of mixed ratio with all pumice sizes on the
amount of micropores were not signi cant.
Pumice application also reduced the amount of ultra-
micropores compared to the controls (Fig. 5, and 6), but
this may not be important because water in these pores
is not available for plant use (Drzal et al. 1999).
Bulk density of the medium decreased signi cantly
(p<0.01) with the rate of pumice applied to soil medium
in both soils. In soil II, no signi cant e ect of pumice
size on bulk density was obtained, but it became more
important with pumice size in soil I (Fig.7). e bulk
density decreased signi cantly (p<0.01) with increasing
rates of pumice in the medium in all pumice sizes (Fig. 8).
In greenhouse culture, a lower bulk density is desirable
due to easier handling and less root losses during pick
up and transportation (Sahin et al. 2004).
e results of this study indicated that the optimum
air- lled porosity conditions were reached by pumice ap-
plications. While the amount of macropores increased
signi cantly (p<0.01) with increasing rate of pumice
in the medium, the amount of mesopores in one of the
soils decreased. e amounts of micropores decreased
signi cantly (p<0.01) by higher rates of pumice applica-
tion. Pumice application reduced the amount of ultrami-
cropores compared to the controls. Bulk density of the
medium decreased signi cantly (p<0.01) with increas-
ing rate of pumice applied to soil medium. It was clearly
determined that pumice may be e ectively used in spe-
ci c amounts for improving aeration and bulk density
conditions of poorly structured soils.
Conclusions
Pumice application to soil increased the amount of
macropores and decreased the bulk density. It was clearly
determined that pumice may be e ectively used in spe-
ci c amounts for improving aeration and bulk density
conditions of poorly structured soils.
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