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Effect of Pesticides on Nitrogen Fixation Activity of Lentil (lens Culinaris Medik.)

S. M. IMAMUL HUQ
Departmet of Soil, Water and Environment, University of Dhaka, Dhaka-1000, Bangladesh

RAQUIBUL AMINl
IUCN Country Office, Dhaka, Bangladesh

R. SADIA AFROZ
BCSIR Laboratories, Dhaka, Bangladesh.

Abstract/ Executive Summary:

Relative compatibility of two selected pesticides at two levels of application (recommended dose and four times of recommended dose) with lentil-rhizobia symbiosis was tested. Better growth was observed in the Melandaha soil than in Bhatpara soil. Detrimental effect was more pronounced in Bhatpara soil. Both the pesticides proved detrimental at four times of recommended dose to nodulation and N₂ fixation. The detrimental effect was more severe when sterile soil was inoculated . Nodulation in Bhatpara soil was decreased by more than 44 and 54% with diazinon in sterile and inoculated soils respectively, while the N₂ fixation was decreased by ca. 12 and 67%, respectively under similar conditions .

Keywords: Pesticides, Nitrogen fixation, Lentil

Location: Savar, Dhaka

Start Date:

End Date:

Program Area: Pest Management

Commodity: Insecticide

Objectives:

To get an idea of in vitro effect of pesticides on pure culture of Rhizobium as well as the in situ effect of pesticides on its symbiotic relationship with its host plant.

Methodology:

Two soils representing Melandaha and Bhatpara series were used in the present study. Both the soils were collected from adjacent areas of Savar. A composite sample was collected to a depth of 15 cm in both the cases. Before use, each sample was screened for debris, roots and other dead plant materials and sieved in a field moist condition to pass through a 2 mm sieve. Sub samples were removed and stored at subzero temperature in sealed polyethylene bags for studies requiring field moist and freshly air-dried soil samples . The remainder of each of the samples was air dried, crushed gently to pass a 2 mm screen, and stored at room temperature in a tightly sealed plastic container. The two soils were found as sandy loam and a silty clay loam after particle size analysis performed by hydrometer method as described by Day and subsequent textural class determined by following Marshall's triangular co ordinates as designed by USDA. The water holding capacity of soils was found to be in the range 49.6 - 58.8% as determined by the method described by Harding and Ross. Results of soil analysis are presented in. Lentil (Lens culinaris. Medic.) was taken as the test plant and cross inoculating Rhizobium leguminosarum as inoculant for studying the effect of pesticides both on symbiotic nitrogen fixation and nitrogen fixing bacteria. The whole study was divided into various segments as described in the following part . Isolation of Rhizobium from root nod ule: Rhizobium strain was isolated from lentil plant growing on soil of Melandaha series. Isolation was performed as described by Clark using yeast extract mannitol agar.

Pesticides were applied aseptically one week after germination. Cotton stoppers were removed when plants reached the base of the cotton stoppers. Both the sets were then left under natural condition. Additional protection was provided with iron gauge hood. At 25, 40, and 55 days after germination, plants were carefully uprooted. The uprooted plants were then gently washed in tap water to remove the adhering soil from the roots and nodules. The numbers of nodule were then counted. Shoots and roots were dried separately in the oven at 70°C for 48 hours . Dry weight of shoots and roots were taken and ground separately in a mortar. Ground shoots and roots were then analyzed for total nitrogen by alkali distillation method . Then the amount of N fixed per plant was calculated by deducting the total N content per seed from the total N content per plant as outlined by Imamul Huq and Larher.

Source of Information: Dhaka Univ. J. Biol. Sci. 13(2): 157-172, 2004 (July)

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The foregoing discussion clarifies the trend of nitrogen fixation observed during the term of the experiment . It is also found that diazinon and heptachlor when used at the recommended dose have negligible ill effect vis-a-vis nodulation , growth and N₂ fixation . But under repeated use concentration of pesticides in the field might rise far above recommended dose that may cause fatal consequences in respect of growth, yield, nodulation and N₂ fixation.

Knowledge Management: Journal