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Effect of Three Insecticides on Soil Microorganisms

M. S. Miyan
Bangladesli Rice Research lnstitute (BRRI), Gazipur-1701, Bangladesh

M. Haq
Bangladesli Rice Research lnstitute (BRRI), Gazipur-1701, Bangladesh

A. N. M. R. Karim
Bangladesli Rice Research lnstitute (BRRI), Gazipur-1701, Bangladesh

N. I. Bhuiyan
Bangladesli Rice Research lnstitute (BRRI), Gazipur-1701, Bangladesh

A. B. M. S. lslam
Bangladesli Rice Research lnstitute (BRRI), Gazipur-1701, Bangladesh

Abstract/ Executive Summary:

The effects of phosphamidon, diazinon, and carboluran on the microorganisms present in the rhizosphere of an irrigated rice crop of BR II was studied in the transplanted Aman season. Pliosphamidon (Dimecron 100 WSC) and diazinon (Diazinon 60 EC) were applied as foliar sprays at 0.85 and 1.0 liter a.i. per ha, respectively, at a calibrated spray volume of 700 litres per ha, and carbofuran (Furadan 3G) as paddy water application at 0.5 Kg a.i. per ha. Applications of the insecticides at 35 and 55 days after transplanting reduced the polulations of Azotobacter, sulphate-reducing, and iron-reducing bacteria in varying degrees. Phosphamidon and carbofuran reduced the number of Azotobacter hy 41 and 42%, respectively, followed by diazinon (29%). The highest reductions of sulphate-reducing and iron-reducing bacteria were obtained in carbofuran (56 and 37%), followed by diazinon (47 and 26%) and phosphamidon (41 and 19%).

Keywords: Insecticides, Azotobacter, sulphate-reducing bacteria, Iron-reducing bacteria, Rice rhizosphere.

Location:

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Insecticide

Objectives:

To study the effects of three widely used insecticides (phosphamidon, diazinon, and carboluran) on Azotobacter, sulphate-reducing bacteria, and iron-reducing bacteria commonly present in rice rhizosphere.

Methodology:

The trial was conducted in 1988 transplant Aman season at BRRI farm, Gazipur. A 850 sq. metre field was laid out in a randomized complete block (RCB) design with four replications, and rice variety BRRU was planted as an irrigated crop in unit plots of 8 x 5 square metres. The following treatments were given: (a) phosphamidon spray (Dimecron 100 WSC) at 0.85 litre a.i. per ha., (b) diazinon spray (Diazinon 60 EC) at 1.0 litre a.i. per ha .. (c) carbofuran (Furadan 3G) at 0.5 Kg a.i. per ha. as paddy water application, and (d) untreated control. All the plots were surrounded by mud levees with one-metre irrigation channel between plots. The insecticides were applied twice. 35 and 55 days after transplanting (OAT). Sprayable insecticides were applied with a knapsack sprayer over the rice canopy at a calibrated spray volume of 700 litres per ha. Soil samples. taken randomly from five spots of each plot, were composited into one for analysis and identification of microorganisms. The soil samples were collected from the middle of 4 rice hills in each spot upto a depth of 15 cm at the following frequencies (a) First sample - 15 OAT but prior to first insecticide application: (b) Second sample - 3 days after the first insecticide application. i.e. 38 OAT; (c) Third sample - 3 days after the second insecticide application, i.e. 57 OAT; (d) Fourth sample - 30 days after the first insecticide application. i.e. 67 OAT: and (e) Fifth sample - 30 days after the second insecticide application. i.e. 85 OAT. Each of the soil samples was mixed thoroughly and passed through mesh sieve and was diluted serially upto 10-6 with Ringer's solution. One ml of each soil dilution was added to a set of 5 tubes each containing 10 ml mediurn suitable for Azotobacter growth. The medium had the following composition: (a) Mineral salts solution -5g of K₂HP0₄; 2g of MgS0₄. 7H₂0; Ig of CaS0-l: O.2g of FeS04; O.2g of MnS04; 0.1 g of Mo0₃, H:p; 0.1 g of KI; and 1000 ml distilled water: and (b) Sucrose-mineral salts solution-100 ml of mineral salt solution; 109 of sucrose; 3g of CaCO; and 900 ml distilied water. The inoculated tubes were incubated one week for Azotobacter, and 3 weeks for others. The bacterial populations were determined by the "Most-Probable-Number" (MPN) method .

Source of Information: Bangladesh J. Sci. Res. 11(2): 175-178, 1993 (December)

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The organophosphate insecticide diazinon, used in soil in granular form or as sprays on the foliage of beans (Phaseolus vulgaris I.), has been reported to affect the number as well as the type of microorganisms present in the rhizosphere of beans. Results further showed that repeated applications of the insecticides were more detrimental to the microbes of rice rhizosphere, as the populations of all the microorganisms decreased further after the second application of the insecticides. The adverse effect of the insecticides was presistent and continued upto 30 days after insecticide application. The residual effect of the insecticides on the microbes could not, however, be ascertained as the sampling was restricted upto 30 days after insecticide application. Azotobacter, sulphate-reducing and iron-reducing bacteria are important microorganisms of the rice rhizosphere because of their direct involvement in the availability of nitrogen, sulphur, and iron nutrients in wetland rice. Certain insecticides used in this study, can decrease their population. On the other hand, use of insecticides is an important component of an "integrated pest management" (IPM) system, and it will continue to be so for increased crop production. Since the effects on microorganisms vary with the type of insecticides, laboratory and field evaluations are necessary to identify relatively safer insecticides. At the same time it is . necessary to determine the critical level of microbial populations required to maintain satisfactory nutritional process of crop plants.

Knowledge Management: Journal