MSc

An experiment was conducted at the College of Agriculture, Vellayani, during 1992 – 93 for modelling carbofuran movement and sorption in soils with varying physic – chemical properties. Undisturbed vertical and horizontal soil columns were used for the study.
Five major locations of the state cropped to banana were selected for the study viz. Malappuram (Ultisol), Chengannur (Inceptisol), Kayamkulam (Entisol), Nedumangad (Mollisol) and Kuttanad (Entisol). The soils exhibited wide variation in the major physico – chemical properties such as texture, water holding capacity, bluk density, particle density, hydraulic conductivity, CEC, AEC and organic matter. The mineralogy of the clay samples had revealed the occurrence of Kaolinite, quartz and smetite as major minerals in these soils.
Distribution of carbofuran in the vertical soil columns showed high concentration of carbofuran at lower depths in the first observation for the Inceptisol of Chengannur and the Entisol of Kayamkulam. While in the 6th observation, the Ultisol of Malappuram, Entisol of Kuttanad and the Mollisol of Nedumangad showed higher concentrations in the lower layers due to higher adsorption.
Horizontal distribution of carbofuran was very low though significant differences were observed between soils. Maximum horizontal distribution was observed in the Entisol of Kuttanad and the least for the Entisol of Kayamkulam.
Regression equation of soil properties on carbofuran content indicated significant influence for organic matter and clay content. Path coefficient analysis of soil properties revealed significant direct positive effect for organic matter and significant direct negative effect for clay content. Indirect negative effects expressed through pH, clay content, Bulk density and AEC with respect to organic matter was not strong enough to counteract the direct positive effect. Similarly the indirect positive effect contributed by clay through organic matter, CEC and sesquioxide was also not sufficient to overcome the direct negative effect.
Concentration of carbofuran in the leachate showed highest values for the Inceptisol of Chengannur followed by the Entisol of Kayamkulam, both having low CEC, organic matter and clay content. The Ultisol of Malappuram with high organic matter, CEC and clay had given the lowest value for carbofuran in the leachate.
Persistence of carbofuran of was maximum in the Mollisol of Nedumangad with high organic matter, clay content and CEC. Persistence was poor in the Inceptisol of Chengannur and the Entisol of Kayamkulam which are low in organic matter, clay content and CEC. Persistence was poor in the Inceptisol of Chengannur and the entisol of Kayamkulam which are low in organic matter, clay content and CEC. The only transformation product identified was 3 – keto carbofuran observed in the surface soil of Ultisol of Malappuram and Mollisol of Nedumanged in the last observation made at 80 days after application.