Soil & Environ. 28(1): 56-59, 2009
www.se.org.pk
Impact of five insecticides on chickpea (Cicer arietinum L.)
nodulation, yield and nitrogen fixing rhizospheric bacteria
H. Khan*, A. Zeb, Z. Ali and S.M. Shah
Nuclear Institute for Food and Agriculture (NIFA), Tarnab, Peshawar, Pakistan
Abstract
A field experiment was conducted to study the effect of five insecticides i.e. Lorsban (40% EC), Decis (25%
EC), Pyrifos (40% EC), Karate (25% EC), and Ripcord (10% EC) on the survival of rhizosphere N2-fixing
microorganisms, nodulation, pod damage (by pod borer), and grain yield of chickpea (Cicer arietinum L.) crop. The
study revealed that Pyrifos suppressed nodulation in chickpea and specific rhizobial counts in the crop rhizosphere,
indicating that this insecticide was harmful to rhizobial population in rhizosphere. All the other tested insecticides
were safe as they did not affect nodulation of the crop and the specific rhizobial counts in the rhizosphere. The
results also revealed that all the tested insecticides except Lorsban (40% EC) suppressed Azotobacter population in
the rhizospheric soil indicating that Lorsban was harmless to Azotobacter while all other tested insecticides were
harmful to the survival of this important nitrogen fixing bacterium. Pyrifos proved to be the most effective
insecticide in controlling the pod borer damage and also in increasing the grain yield significantly as compared to
other tested insecticides.
Key words: Insecticides, nodulation, rhizosphere, Rhizobium, Azotobacter, plant infectivity test
Introduction
Chickpea (Cicer arietinum L.) is the major rabbi pulse
crop grown on low fertility sandy loam soils in Pakistan.
The area under chickpea cultivation in the country is 1.028
million hectares with average production of 466 kg ha-1
(Agriculture Statistics of Pakistan, 2006-07). Being a
leguminous crop, chickpea has an inbuilt genetic capability
to produce root nodules if its specific Rhizobia are present
in the rhizospheric soil. Normally in Peshawar Valley and
other chickpea growing areas of NWFP (Karak, Lukky
Marwat etc), the crop is naturally nodulated (Idris et al.,
1980) indicating the presence of indigenous chickpea
rhizobia in sufficient number in the rhizospheric soil.
Brockwell and Robinson (1970) also reported consistent
relationships between vegetation, particularly legumes, and
number and types of rhizobia in the rhizosphere.
Besides having high nutritive value, chickpea enriches
the soil by virtue of its high symbiotic nitrogen fixing
ability. However, chickpea yield is significantly low that
could be attributed to many factors including insect pests
and chickpea pod borer being the major economic pest. The
pod borer (Helicoverpa armigera) damages the crop
extensively (Read et al., 1980; Lal et al., 1985; Naresh and
Malik, 1986; Deka et al., 1987; Gohoker et al, 1987;
Biradar et al., 1999; Mahmood and Shah, 2003) as it feeds
on tender shoots and young pods. According to Joginder et
al., (1990) damage to pods and seed varies from 13.684.3% and 3.1-84.3%, respectively. These losses to the crop
can be reduced by the application of insecticides (Gohokar
et al., 1987; Birader et al., 1999). Usually farmers spray the
crop with different insecticides for the control of various
insect pests. Ultimately after spray, these insecticides fall
upon the soil directly during spray or indirectly with rain
and dew water. A part of these insecticides penetrates into
the rhizosphere of the soil with potential to affect soil
microflora. Rager et al. (1994) noticed negative effect of
pesticides on soil and water microflora of wetland rice
fields.
The objective of the present study was to investigate
the effect of five commonly used insecticides on the
survival and population of rhizospheric nitrogen fixing
microorganisms, natural nodulation, pod borer damage and
grain yield of chickpea crop.
Materials and methods
In a field trial, effect of five insecticides i.e. Lorsban
(40 %EC, 875 mL acre-1 ), Decis (25% EC, 200 mL acre-1)
Pyrifos (40% EC, 1125 mL acre-1), Karate (25% EC, 250
mL acre-1) and Ripcard (10% EC, 225 mL acre-1) was
investigated on chickpea nodulation, population of nitrogen
fixing bacteria in the rhizosphere, damage by pod borer and
grain yield of chickpea during rabbi 2001-02 at the research
farm of Nuclear Institute for Food and Agriculture (NIFA),
Peshawar located at 34 oN, 71 oE at an altitude of 972 ft.
Chickpea cultivar NIFA-95 was used as a test crop. Sowing
was done in rows with row-to-row distance of 40 cm and
plant-to-plant distance of 15 cm in the plots size of 20 m2.
Six treatments including control were replicated four times
in RCB design. A uniform basal dose of N, P and K at 20,
60 and 40 kg ha-1 was applied at the time of sowing as
Urea, SSP and K2SO4, respectively. Each insecticide was
*Email: mails@nifa.org.pk
© 2009, Soil Science Society of Pakistan (http://www.sss-pakistan.org)
Khan, Zeb, Nawaz and Amir
sprayed 45 days after planting and at pod initiation stage.
Indigenous population of chickpea Rhizobia and
Azotobacter at the time of sowing as determined by plant
infectivity test was 3.1 x 103 cells g-1 soil (Vincent, 1970)
and 1.3 x 103 g-1, respectively, by MPN Technique
(Francis,1965). Physico-chemical properties of soil at the
experimental site were determined (Rhoades, 1982). The
soil was poor in nitrogen and organic matter and was free of
excessive salts (Table 1).
Table 1. Phyisco-chemical analysis of the experimental
field
Soil property
pH (1:2.5 suspension)
EC (dS m-1)
Organic matter (%)
CaCO3 (%)
Nitrogen (%)
Phosphorus (P2O5 mg kg-1)
Textural class
Value
8.00
0.50
0.96
11.20
0.05
14.20
Silty clay
Data on nodulation (number and nodules fresh weight
plant-1) were recorded at 50% pod formation stage. For this
purpose, three plants were randomly selected (one in the
centre of the central row and two at the opposite corners of
each plot). These plants were uprooted with the help of
spade by making a 40 cm deep pit approximately 30 cm
around the plant. Samples from the adhering soil to the
roots were collected from each treatment including control
and were analyzed for chickpea rhizobial counts (cells g-1 of
soil) by plant infectivity test (Vincent, 1970) and for
Azotobacter by MPN method (Francis, 1965).
The roots were thoroughly washed and the nodules
were detached with the help of forceps and collected in a
Petri dish. Number of nodules and fresh weight of nodules
plant-1 were recorded. The crop yield data and pod borer
incidence were recorded by Entomology Division of NIFA.
The percent damage of pods was calculated as under
(Rashid et al., 2003).
pod damage (%)= No. of damaged pods x 100
No. of total pods
Grain samples were dried in oven at 70 OC for 48
hours. After grinding, grain N and protein content were
determined by Kjeldhal method (Bremner, 1982). The data
were analyzed statistically according to DMRT (Steel and
Torrie, 1982).
Results and discussion
Effect on nodulation
The study revealed (Table 2) that all the tested
insecticides were safe for chickpea nodulation except
57
Pyrifos (organophosphate group) that significantly
suppressed the natural nodulation as compared with other
tested insecticides. It has been assumed that the
agrochemicals, accumulated due to extensive application to
soil, may cover the rhizobium recognition sites on the root
surface of legumes resulting in reduced nodulation
(Mussarat and Haseeb, 1999).
Table 2.
Effect of insecticides on natural nodulation of
chickpea (at 50% pod formations stage)
Treatment/
Insecticide
Lorsban (40% EC)
Decis (25% EC)
Pyrifos (40% EC)
Karate (40% EC)
Ripcord (10% EC)
Control (No. insecticide)
No. of
nodules
plant-1
25 a
22 a
10 b
25 a
26 a
25 a
Fresh weight
of nodules
(g plant-1)
2.3 a
2.0 a
1.1 b
2.2 a
2.0 a
2.0 a
Each figure is average of four replicates
Figures sharing the same letters do not differ significantly at 5%
level of probability according to DMRT (Steel and Torrie,
1980).
Effect on nitrogen fixing bacterial population
The specific rhizobial counts g-1 of rhizospheric soil as
determined by plant infectivity test revealed (Table 3) that
Pyrifos (40% EC) significantly suppressed the population
of specific chickpea Rhizobia from 2.1 x 105 cells to 2 x 104
cell g-1 of rhizospheric soil (90 % reduction as compared to
control). All the other tested insecticides did not affect the
population of chickpea Rhizobia significantly in the
rhizospheric soil. The study also revealed (Table 3) that
except Lorsban (40% EC), all the tested insecticides
suppressed the Azotobacter population (free living nitrogen
fixer) in the rhizosphere. According to Hang et al. (2001),
application of herbicide Butachlor stimulated the growth of
nitrogen fixing and nitrifying bacteria in the beginning but
reduced greatly afterwards in paddy soil. Other workers
have also reported varying effect of different pesticides on
soil bacteria (Allievi et al., 2001; Ghaury et al., 2001; Min
et al., 2001; Athiana et al., 2003 and He et al., 2006).
Effect on pod borer damage and grain yield
The study revealed (Figure 1) that pod borer damage
was minimum and significantly lower in the treatment
sprayed by Pyrifos (only 9.72% damage) as compared to
control (68.9% damage) indicating that Pyrifos was the
most effective in controlling the damage inflicted by pod
borer as compared to four other tested insecticides. Grain
yield (Figure 1) was also significantly higher (1290 kg ha-1)
Impact of five insecticides on chickpea
58
Table 3. Effect of different insecticides on Rhizobial and Azotobacter population in Chickpea rhizosphere
Chickpea Rhizobia
(counts g-1 of soil)
2.0 x 105
1.2 x 105
2.0 x 104
1.1 x 105
1.0 x 105
2.1 x 105
Treatment/ Insecticide
Lorsban (40% EC)*
Decis (25% EC)
Pyrifos (40% EC)
Karate (40% EC)
Ripcord (10% EC)
Control (No. insecticide)
Azotobacter
(counts g-1 of soil)
2.0 x 105
5.5 x 104
5.0 x 104
4.5 x 104
4.0 x 104
1.9 x 105
*EC = Emulsify able concentrate
in treatment receiving Pyrifos as compared to all other
tested insecticides and control (only 105 kg ha-1). Simon
and Sydney (2000) evaluated different insecticides for the
control of Helicoverpa armigera on soybean and found that
only Chloropyrifos (Pyrifos) showed significant activity
one week after treatment. Mahmood and Shah (2003) also
tested different insecticides and found that Chloropyrifos
proved to be the best in reducing pod damage and in
increasing biomass and grain yields which are in close
agreement with the results of the present study.
Grain Yield
% Damage
70
60
1000
50
800
40
600
30
400
% Damage
-1
Grain yield (kg ha )
1200
20
200
10
0
0
Lorsban
Decis
Pyrifos
Karate
Ripcord
Treatment/
Insecticide
Lorsban
Decis
Pyrifos
Karate
Ripcord
T6 Control
%
Nitrogen
4.23 a
4.12 a
4.20 a
4.25 a
4.18 a
4.12 a
N-uptake
(kg ha-1)
22.2 b
22.0 b
54.2 a
25.7 b
23.2 b
4.30 c
%
Protein
26.4 a
25.7 a
26.2 a
26.6 a
26.1 a
25.7 a
Each figure is average of four replicates.
Figures sharing the same letters do not differ significantly at 5%
level of probability.
80
1400
Table 4. Effect of insecticidal spray on percent
nitrogen, percent protein and nitrogen
uptake in grains
Control
Figure 1. Effect of insecticides on pod borer damage
and grain yield of chickpea
Effect on nitrogen and protein contents in
grains
Nitrogen and protein contents of grain were not
affected significantly while nitrogen uptake showed
significant variations (Table 4). The study revealed that
although the insecticide Pyrifos proved effective in
managing pod borer damage yet it was harmful to chickpea
Rhizobia in the crop rhizosphere by decreasing its survival
significantly. So, the crop sprayed by Pyrifos for pod borer
control, increased the grain yield at the cost of decreased
nitrogen fixing capability of the crop by suppressing the
rhizobial population in the rhizosphere and spray before
pod formation is very harmful thus resulting in decreased
natural nodulation in the crop. Mussarat and Haseeb (1999)
attributed this decrease in nodulation to the protection of
rhizobium recognition sites by extensive application and
accumulation of agrichemicals (paraquat) on the root
surface of legumes. This is exactly like the side effect of
antibiotics.
However, the profit due to Pyrifos spray, (by decreased
pod borer attack and increased grain yield), was several
hundred times more as compared to the loss in nitrogen
fixation due to decreased nodulation.
Pyrifos and all the tested insecticides except Lorsban,
suppressed the population of Azotobacter in the crop
rhizosphere. Lorsban, however, slightly enhanced the
growth and survival of this valuable nitrogen fixing
bacterium. Lu et al. (2003) also reported stimulating effect
of herbicide Quinclorac on the growth and survival of
nitrogen fixing bacteria in paddy soil.
It can be concluded from the present study that
chickpea crop should be sprayed with insecticide Pyrifos
(only at pod formation stage because earlier sprays affected
the nodule formation and beneficial microbial population in
the rhizosphere) for the effective control of pod borer
attack.
Khan, Zeb, Nawaz and Amir
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