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

S. M. lmamul Huq
Departmet of Soil, Water and Environment, University of Dhaka, Dhaka-1000, Bangladesh.

Raquibul Amini
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: Melandaha and Bhatpara soil series, Savar, Bangladesh

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Lentil

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:

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. pH of the soils was measured by a combined electrode pH meter at a soil: water ratio of 1 : 2.5. Available soil phosphorus was extracted by 0.5M NaHCO₃ and phosphorus content of the extracts were determined colorimetrically using ascorbic acid as the reductant as described by Murphy and Riley. After 20 - 25 days, when satisfactory plant growth was obtained, plants were uprooted and roots were examined for the presence of nodules. Presence of nodules only in the inoculated plants was taken as the indication of the effectiveness of the isolated strain. Several representative nodules were selected and Rhizobium was reisolated on YMA medium containing 0.0025% Congo red. Characteristic growth on the YMA-Congo red medium profoundly proved the authenticity of the isolate. 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.

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

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

In the current study total N₂ fixed at different time interval w ere found to differ; there was an initial low N₂ fixation which then reached a pick at second observation and decreased again at final observation. The N₂ fixation profile is consistent with that proposed. 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