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Effect of Insecticides on Soil Microorganisms, Natural Enemies and Soil Chemical Properties in Rice Field

Dr. Mainul Haq
CSO and Head
Entomology Division, BRRI, Gazipur-1701

Sheikh Shamiul Haque
SSO
Entomology Division, BRRI, Gazipur-1701

Md. Shahjahan Kabir
SSO
Plant Pathology Division, BRRI, Gazipur-1701

Abstract/ Executive Summary:

Three commonly used insecticide (carbofuran 5G, diazinon 10G and chlorpyrifos 20EC) did not have any effect on soil chemical properties. However, these insecticides reduced the population of the bacteria Agotobacter sp. by 3.22 to 3.66%. All these three insecticides were also found to have detrimental effect on spiders (population decreased 34 - 70%).

Keywords: Insecticide, Soil microorganism, Natural enemy, Azotobacter

Location: BRRI, Gazipur

Start Date: 01-07-2006

End Date: 30-06-2007

Program Area: Pest Management

Commodity: Insecticide

Objectives:

To determine the effect of insecticides on soil chemical properties, microorganisms present in soil and on natural enemies of rice insect pests

Methodology:

Three commonly used insecticides, carbofuran 5G, diazinon 10G, chlorpyriphos 20EC and an untreated control were designed in RCB with four replications during T. Aman 2006 and Boro 2007. The unit plot size was 5m X 8m. The insecticides were applied at recommended rate. Two applications of insecticide at 30 DAT and 45 DAT were applied in each season. Natural enemy population was estimated by direct hill count (20 hill/plot) before and after three days of insecticide application. For soil chemical properties initial soil samples (0-15 cm) were collected prior to transplanting in T. Aman 2006. At Boro 2007, the post harvest soil samples were collected. Samples were analyzed for chemical properties (organic carbon, total N, available P and exchangeable K). Soil samples were collected at five different dates (29, 33, 48, 60 and 75 DAT) in both T. Aman and Boro season. Soil bacteria Azotobacter were counted from the soil of 5th sample. Ten gm soil was diluted in 250 ml sterile water and then a dilution series of 10 -1 to 10 -6 was made. From each series 1 ml soil dilution was added to a set of 5 tubes containing 10 ml Azotobacter growing medium. The inoculated tubes were incubated for one week and the bacterial populations were determined by ' Most probable number' method.

Source of Information: Proceedings of BRRI Annual Internal Review for 2006-2007

Article Link (Online Journal):

Funding Source:

1. Government

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Overall populations of natural enemies were low. Most commonly found natural enemies were spider, carabid beetle and ladybird beetle. Spider population was comparatively higher than the others. In T. Aman 2006, spider population was increased after insecticide spray at 30 DAT. But it sharply decreased at 45 DAT. Similarly, carabid beetle population sharply decreased in all the treated plots and increased in control plot at 30 DAT. In Boro 2007 season spider population sharply decreased after insecticide spray at 45 DAT. No yield differences were observed among the treatments. Effect on soil chemical properties and microorganisms present in soil: No significant differences were observed among the treatments in all the chemical properties of soil tested. The number of Azotobacter in 10 gram soil was 1488, 1465, 1313 and 40,700 respectively in carbofuran 5G, diazinon 10G, chlorpyriphos 20EC and control plots respectively. It is remarkable that the action of all insecticides was toxic enough to reduce bacterial populations present in the rice rhizosphere.

Knowledge Management: Report/Proceedings