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Effect of Insecticides on Soil Microorganisms

A. A. Masum Billah
Agriclture Extension Officer
Department of Agricltural Extension, Iswardi, Pabna, Bangladesh

M. H. Ferdous
Department of Genetics and Plant Breeding, Sher-e-Bangla Agricultural University, Dhaka-1207, Bangladesh

T. Taufique
Department of Horticulture, Sher-e-Bangla Agricultural University, Dhaka-1207, Bangladesh

H. Mehraj
Department of Horticulture, Sher-e-Bangla Agricultural University, Dhaka-1207, Bangladesh

A.F.M. Jamal Uddin
Department of Horticulture, Sher-e-Bangla Agricultural University, Dhaka-1207, Bangladesh

Abstract/ Executive Summary:

An experiment was conducted in the laboratory of the Department of Agricultural Chemistry, Sher-e-Bangla Agricultural University, Bangladesh from July to December, 2008 to know the impact of 4 selected insecticides (i.e., Diazinon 60 EC, Marshal 20 EC, Dursban 20 EC and Admire 200 SL) on soil microorganisms. The impact was expressed as amount of CO₂ evolution/gram soil and dehydrogenase activity (TPF formation). CO₂ evolution in soils indicates a great activity of soil microorganisms and maximum CO₂ evolution was found from Marshal 20 EC (74.8, 281.2 and 142.4 μg/g soil) at 2, 8 and 24 days of incubation while Admire 200 SL (126.5 and 222.4 μg/g soil) at 4 and 16 days of incubation. Diazinon 60 EC (0.073, 0.075, 0.079, 0.072 and 0.067 μmole/ml at 2, 4, 8, 16 and 24 days of incubation respectively) had maximum TPF formation.

Keywords: CO2 evolution, TPF formation, Incubation

Location: The laboratory of the Department of Agricultural Chemistry, Sher-e-Bangla Agricultural University, Bangladesh

Start Date: 00-07-2008

End Date: 00-12-2008

Program Area: Crop-Soil-Water Management

Commodity: Insecticide

Objectives:

Objective of the study was to know the impact of four selected insecticides (i.e., Diazinon 60 EC, Marshal 20 EC, Dursban 20 EC and Admire 200 SL) on soil microorganisms.

Methodology:

The experiment was conducted in the laboratory of the Department of Agricultural Chemistry, Sher-e-Bangla Agricultural University (SAU), Dhaka, Bangladesh, during the period from July to December, 2008. Soil sample was collected from the farm of SAU and brought to the laboratory. Then spread for partial air drying after removal of plant roots, insects, worms and small pieces of organic matter and passed through 2 mm mesh sieve. After sieving, soil was pre-incubated in the laboratory. Pre-incubation of soil: Soil with 40% water holding capacity was subjected to pre-incubation aerobically at room temperature for 10 days. This allowed the soil microbial population to stabilize, minimize the effects of soil handling and preparation. Immediately after conditioning the soil was used for the experiment. Treatments: Four treatments viz., Diazinon 60 EC @ 3.0 ml/L, Marshal 20 EC @ 2.0 ml/L, Dursban 20 EC @ 2.0 ml/L, Admire 200 SL @ 4.0 ml/L and control (untreated) were used in the experiment following a Completely Randomized Design (CRD) with three replications. Procedure for determination of soil microbial activity: Sixty gram dry soil was weighed in a 100 ml glass jar and 5 ml of insecticide solution was injected inside the soil of the jar for each treatment. Five milliliters of distilled water was added to the control soil (untreated) to maintain moisture content equivalent to those of treated soils. Following insecticide application, glass jars were placed in 1L glass bottles. To trap CO₂ evolved by soil microorganisms during each incubation, 20 ml of 1M NaOH solution was taken in a small glass bottle and placed inside the jar. The 1L glass bottles were sealed and incubated for 24 days at room temperature. To maintain internal humidity of 1L glass bottle, 10 ml of distilled water was added at the bottom of each incubation bottle. The amount of CO₂ evolved due to soil microbial respiration was determined after 2, 4, 8, 16 and 24 days of incubation. Microbial respiration: Microbial respiration was monitored as CO₂ evolution from soil samples after 2, 4, 8, 16 and 24 days of incubation. Fresh NaOH was replaced at each sampling. The trapped CO₂ was titrated with standard (0.09N) HCl using pH meter. Microbial activity was expressed as μg CO₂-C evolved g^-1 soil. The amount of total CO₂-C was determined by using the formula. Substrate solution (TTC), 1% TTC solution: 3 g of 2, 3, 5-triphenyltetrazolium chloride was dissolved in 100 ml ethanol. The solution was stored for one week at 4ºC in dark or in amber bottle. Glucose solution: For preparing glucose solution 1 g of glucose was dissolved in 100 ml distilled water. Triphenyl formazan (TPF) solutions: A standard solution of 0.0002 M triphenyl formazan was prepared by dissolving 0.03 g triphenyl formazan in 500 ml ethyl alchol. Data analysis: Collected data were statistically analyzed using MSTAT-C Computer Package Program. The significance of the differences among the treatment means were estimated by the Least Significance Difference (LSD) test at 1% level of probability.

Source of Information: Int. J. Expt. Agric. 4(4):24-28, 2014

Article Link (Online Journal):

Funding Source:

1. Government

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Insecticides have a recognizable effect on the soil microbial activity as CO₂ evolution. In case of dehydrogenase activity, Diazinon 60 EC, Admire 200 SL and Marshal 20 EC gave greater positive effect than the control (untreated). In this experiment only the duration of incubation is considered but temperature varies in summer and winter drastically and soil become saturated in the monsoon in Bangladesh. As a result, the soil pH has changed. This is why further experiment is needed on the temperature, carbon sources and pH response on the microbial activity and microbial dehydrogenase activity along with the different insecticides.

Knowledge Management: Journal