Middle East Journal of Applied
Sciences
ISSN 2077-4613
Volume : 06 | Issue :02 | April-June| 2016
Pages: 357-361
Influence of Soil Mechanical Impedance on Growth and Root Penetration of some
Plants
Mashhour A. M. A., Shahin M. M. and Rizk A. H.
Soils and Water Dept., Agric. Faculty, Al-Azhar University, Cairo, Egypt
Received: 5 April 2016 / Accepted: 4 May 2016 / Publication date: 25 May 2016
ABSTRACT
A pot experiment was conducted in the research farm of Agricultural Faculty, Al-Azhar University, Nasr
city, to investigate the effect of mechanical impedance of the soil on the penetration, elongation, root
distribution (number of secondary roots) and biomass of roots and shoots to determine root-limiting bulk density
and cone index for the following plants: wheat (Triticum aestivum L), broad bean (Vicia faba L), pea crab
(Pisum sativum L) and Egyptian lupin (Lupinus terms L). The plants were grown for 40 day under different
compaction states, whereas the soil bulk density values were 1.25, 1.4, 1.55 and 1.7 Mgm-3. The results show
that there are difference between critical limit values of soil bulk density and cone index for the investigated
parameters of plants under studied soil condition. For wheat and pea crab plants, the moderate compaction (1.4
Mgm-3 and 3.2 MPa) had the effect on decreasing the values of root length, root density and biomass of roots
and shoots and consequently, that is the critical limit for both plants. While for Egyptian lupine, the critical limit
of cone index increased to 4.8 M Pa or 1.55 Mgm-3. On the other hand, broad bean parameters are not affected
by the compaction values under study. This means the high ability of broad bean root to penetrate hard soils.
Key words: Bulk density, penetration resistance, compaction, wheat, broad bean, pea crab, Egyptian lupine
Introduction
Soil compaction is the physical consolidation of the soil by an applied force that destroys structure,
reduces porosity, limits water and air infiltration, restricts plant root growth and exploration, increases resistance
to root penetration and subsequently reduce crop yield (Ishaq et al., 2001). Materechera et al. (1991) examined
the effects of increased soil strength on 22 monocot and dicot species; the dicot showed less effect of increased
soil strength on elongation rates of roots than the monocots. Bengough and Young, (1993) showed that the daily
elongation rate of pea roots which were growing through a high bulk density soil was only about 65 % of that of
root which were growing through the weaker low bulk density soil. Atwell, (1993) reported that total root mass
of lupine is not necessarily reduced by mechanical impedance. Also, Sato et al. (1997) concluded that
mechanical impedance is the most appropriate expression for root elongation because it includes the effects of
soil-water content and bulk density. Houlbrooke et al. (1997) found that the increasing subsurface soil bulk
density and low matrix potential had significant effect on root and shoot growth. Goodman and Ennos, (1999)
stated that soil strength affected shoot and root systems of sunflower and maize but had no significant effect on
shoot height. Murphy et al. (2000) noted that root length is more consistently affected by compaction than is
root biomass, with extension throughout the soil profile decreasing with increasing compaction. Liu and shan,
(2003) showed that high soil bulk density and low matrix potential had a significant effect on root and shoot
growth. Guihua and Weil, (2010) evaluated penetration of compacted soil by roots of three cover crops (forage
radish, rapeseed and rye). They concluded that soil penetration capabilities of three cover crops were in the
order of forage radish > rapeseed > rye. Bengough et al. (2011) found that impedance caused physical
limitations to root growth in the rooting zone with a typical soil penetrometer resistance of 2.0 M Pa, the
threshold for root elongation.
Lynch, (2013) reported that the deep roots that are capable of penetrating hard soil are important for
improving crop productivity in compacted soil. Generally the ability of roots to penetrate hard soils is associated
with phenes that reduce the likelihood of root buckling when penetrating hard soils (Clark et al., 2003;
Bengough et al., 2011; Jin et al., 2013). Chimungu et al. (2015) reported that the root anatomical phenes were
found to be better predictors of root penetrability than root diameter per se and associated with smaller distal
cortical region cell size. Smaller outer cortical region cell play an important role in stabilizing the root against
ovalization and reducing the risk of local buckling and collapse during penetration, thereby increasing root
penetration of hard layers. The aim of this paper is an attempt to study the effect of the soil bulk density and
penetration resistance on selected parameters of the plant roots and shoots to determine root-limiting bulk
Corresponding Author: Shahin, M. M., Soils and Water Dept., Agric. Faculty, Al-Azhar University, Cairo,
Egypt
E-mail: [email protected]
357
Middle East J. Appl. Sci., 6(2): 357-361, 2016
ISSN 2077-4613
density and cone index for the following plants: wheat (Triticum aestivum L), broad bean (Vicia faba L), pea
crab (Pisum sativum L) and Egyptian lupine (Lupinus terms L).
Materials and Methods
A pot experiment was conducted in the research farm of Agricultural Faculty, Al-Azhar University, Nasr
city, to investigate the effect of mechanical impedance of the soil on the penetration, elongation, root
distribution (number of secondary roots) and biomass of roots and shoots to determine root-limiting bulk density
and cone index for the following plants: wheat (Triticum aestivum L), broad bean (Vicia faba L), pea crab
(Pisum sativum L) and Egyptian lupin (Lupinus terms L).
Soil characteristics and pot preparation:
Surface soil samples (0 – 20 cm depth) were collected from El-Mansouria, Manchiate Al-Khanater, Giza
Governorate. The soil was transported to the laboratory, air dried on plastic sheets, loosely crushed, and sieved
to remove the > 2 mm fraction. Only the fine earth fraction was used in this experiment to easily soil layers
compaction. Soil samples were taken for routine physical and chemical analysis according to Klute, (1986) and
Page et al. (1982). Tables 1 and 2 show some physical and chemical properties of the investigated soil.
Table 1: Physical properties of the investigated soil
Coarse Fine
Textural
Bulk
Real
Silt Clay
sand sand
class
density density
% %
%
%
Mg m-3 Mg m-3
10
30 22 38 Clay loam 1.25
2.7
Table 2: Chemical properties of the investigated soil
Soluble cations
EC
pH
c mol Kg-1
-1
dSm
1:2.5
Ca Mg
Na
K
1.9
7.3 1.4 0.55
2.9
0.35
Porosity
%
F. C
%
53.7
33
CO3
0.0
Available
water
%
13.5
19.5
W. P
%
Soluble anions
c mol Kg-1
HCO3
Cl
2.4
3.2
SO4
0.6
Hydraulic
conductivity
cm hour-1
2.1
MWD
mm
2.54
OM
%
CaCO3
%
2.2
2.0
Pots (top diameter 20 cm, height 20 cm) were packed by a range of compaction forces to produce a range
of different soil bulk density for separately treatment. Whereas the pots were packed into four layers, each layer
was compacted individually to obtain the required weight for each layer and consequently the weight of pot
divided into the volume gave the soil homogeneous at soil bulk density as follows; 1.25 Mg m-3 for weak
compacted soil (natural soil), 1.4 and 1.55 Mg m-3 for moderate compacted soil and 1.7 Mg m-3 for strong
compacted soil. Cum et al. (1992) used the following equation to predict the cone index in the relation to soil
bulk density and moisture content percentage: CI= (91.46 ln (MV) – 644) 0.862 μ, where CI= cone index (M
Pa), MV= soil bulk density (Kgm-3), μ= moisture content percentage. According to this equation, the values of
soil bulk density 1.25, 1.4, 1.55 and 1.7 Mg m-3 are versus cone index values or caused penetration resistance of
1.4, 3.2, 4.8 and 6.3 M Pa respectively. In this study, soil moisture content expressed by 20 %. The four plants
were grown for 40 days in the previous prepared pots in randomized complete design in three replicates. At the
end of experiment, plant roots were separated from the soil, washed, air dried prior to recording the fresh and
dry weight, length, secondary root number. Also, fresh and dry weights of shoots were determined and the ratio
between dry roots and dry shoots was calculated for all plants and treatments. Data were statistically analyzed
(Snedecor and Cochran, 1980)
Results and Discussion
1. Effect of compaction on root length of plants.
Root length indicates the relative ability of the different plant roots to penetrate the compacted soil layers.
Data in Table 3 show that the root length of plants was significantly affected by soil bulk density or cone index
values, whereas the high values of root length for the almost plants were in the 3.2 and 4.8 M Pa cone index.
This may be due to the medium bulk density may provide longer retention of water in the soil and increase
available water for plants due to the higher proportion of mesopores. On the other hand, the lowest values of
root length were observed with highly cone index and soil bulk density (6.3 M Pa or 1.7 Mgm-3) in all plants
except that in broad bean plant, root length was greater than other treatments. This may be attributed to the
broad bean is a dicot plant and the increase in the thickness of roots for this plant. In this concern, Clark et al.
358
Middle East J. Appl. Sci., 6(2): 357-361, 2016
ISSN 2077-4613
(2008) observed that thicker roots are more resistance to buckling and deflection when encountering hard soil
domains. They reported log-log positive relationships between root diameter and bending stiffness. Also, Jin et
al. (2013) suggested that the ability of roots to penetrate hard soils is associated with synergisms or additive
interactions between root phenes (genotype) such as root growth angle, root hairs and anatomical phenes,
because a combination of greater anchorage of the root tip, reduce axial stress and resistance to root bending or
buckling would work together to improve root penetrability of hard soils.
Table 3: Root length (means cm) of plants as affected by compaction
BD
CI
Porosity
wheat
Mgm-3
M Pa
%
1.25
1.4
53.7
5.00
1.4
3.2
48.15
8.50
1.55
4.8
42.59
6.00
1.7
6.3
37.04
4.90
LSD at 0.005
0.32
Broad bean
Pea crab
Egyptian lupine
9.00
10.40
10.60
11.10
0.57
7.00
7.50
6.00
5.00
0.498
5.90
7.53
7.73
6.00
0.27
2- Effect of compaction on root density (number of secondary roots).
Root distribution is the most important properties of plant which effect on plant growth and crop yield.
The data in Table 4 show that the mean number of secondary roots is significantly affected by soil strength. The
results showed that the roots of plant species differed considerably in their ability to secondary root formation at
different soil strength. However, the root density in wheat and pea crab followed the decreasing order of
moderate cone index > low cone index > high cone index. This may be attributed to the roots type of both plants
was the thinner roots which cannot grow in dense soil. In contrast, the mean number of secondary roots of broad
bean increases with the high values of soil density under study. Similar trend of brad bean was observed with
Egyptian lupine in the weak and moderate treatments, while in the strong compaction, the number of roots is
decreased. Bischetti et al. (2005) stated that root tensile strength decreases with increasing diameter according to
a negative power law. Also, Loades et al. (2013) showed that thicker roots are associated with good penetration
of strong soils by relieving stress at the growing root tip.
Table 4: Root distribution (number) of plants as affected by compaction
BD
CI
Porosity
wheat
Broad bean
Mgm-3
M Pa
%
1.25
1.4
53.7
9.33
20.00
1.4
3.2
48.15
14.00
20.67
1.55
4.8
42.59
11.00
20.67
1.7
6.3
37.04
9.33
22.33
LSD at 0.005
1.197
1.104
Pea crab
Egyptian lupine
4.67
6.00
5.00
4.00
0.99
5.67
7.67
10.33
8.00
0.745
3- Effect of compaction on root and shoot dry matter
Tables 5 and 6 present the biomass of roots and shoots for four plants. Generally, the critical limits of
cone index for root and shoot dry matter varies between plant species. Broad bean (shoot and root) dry matters
were greater significantly under high cone index or soil bulk density than under low and moderate cone index or
soil bulk density (LSD at 0.05 % was 0.037 for root and 0.11 for shoot). On the other hand, wheat and pea crab
dry matters were greater significantly under moderate and low cone index than under high cone index. For
Egyptian lupine, the highest values of roots and shoots dry matter were observed under moderate cone index
(4.8 M Pa) and the lowest values were under low cone index or soil bulk density values. These results in
agreement with those of Atwell (1993), who reported that root mass of lupine is not necessarily reduced by
mechanical impedance. Also, Goodman and Ennos (1999) found that bending strength of maize roots changes
with soil bulk density, with roots from stronger soil being less stiff than those from weak soil.
Concerning the relation between soil bulk density and the root: shoot ratios, Fig. 1 show there were also
differences in root: shoot ratios between treatments. In all plants except slightly variances in Egyptian lupine,
the higher ratios were observed under dense soil than those grown in weak soil. Similar results were obtained by
Materechera et al. (1992). The contrast result founded by Goodman and Ennos (1999). They found that, in
sunflower plants grown in strong soil had significantly lower root: shoot ratios than those grown in weak soil.
Clark et al. (2003) reported that root of different species differ in capacity to penetrate compacted soils where
the sizes of soil pores are smaller than their diameters, and it has been suggested that roots with greater diameter
may be better able to penetrate compacted soils than roots with smaller diameters. Studies by Ishaq et al. (2001)
suggested that incorporating species with a deep tap root system in the rotation was desirable to minimize the
effects of soil compaction.
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Middle East J. Appl. Sci., 6(2): 357-361, 2016
ISSN 2077-4613
Table 5: Mean values of root biomass (gm plant-1) as affected by compaction
BD
Wheat
Wheat
Broad
Broad bean Pea crab
Mgm-3
FW
DW
bean
DW
FW
FW
1.25
0.217
0.117
1.033
0.267
0.223
1.4
0.317
0.167
1.300
0.333
0.317
1.55
0.267
0.150
1.333
0.350
0.273
1.7
0.250
0.117
1.617
0.417
0.187
LSD at 0.005
0.05
NS
0.047
0.037
NS
Table 6: Mean values of shoot biomass (gm plant-1) as affected by compaction
BD
Wheat
Wheat
Broad
Broad
Pea crab
Mgm-3
FW
DW
bean
bean
FW
FW
DW
1.25
3.533
0.700
8.600
1.533
4.800
1.4
3.700
0.767
9.300
1.700
4.900
1.55
3.500
0.600
9.567
1.750
4.500
1.7
3.333
0.433
10.500
1.800
3.800
LSD at 0.005
0.12
0.09
0.115
0.11
0.22
Pea crab
DW
0.100
0.150
0.117
0.100
0.029
Pea crab
DW
0.733
0.833
0.600
0.417
0.15
Egyptian
lupine
FW
0.200
0.300
0.350
0.307
0.012
Egyptian
lupine
FW
4.700
6.300
6.600
6.400
0.2
Egyptian
lupine
DW
0.103
0.150
0.207
0.153
0.005
Egyptian
lupine
DW
0.600
0.717
0.767
0.700
0.013
Fig. 1: The effect of soil compaction on the root: shoot ratio of plants
The abovementioned results concluded that the effect of compaction on the investigated parameters of plants
differ according to plants types (monocot or dicot) and the root type (thicker or thinner). Also, this study offered
a glance into how plants under study respond to mechanical impedance of soil and helping in determining the
extent to which plants compensate for changes in soil strength and how changes in the cultivation of specific
crops might reduce losses due to uprooting and lodging. Finally, to better understand the relative importance of
compaction study and it effects on different plants in a cultivated soils need to incorporate into future research.
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