Studies on Sorption, Movement and Persistence of Soil Applied Pesticides in Different Soils.
Rajannan Jayakumar, Tamil Nadu Agricultural Univ, Dept of Soil Science and Agricultural Chemistry, Coimbatore, India
The adsorption and desorption studies were conducted in alluvial, black, laterite and red soil taking four soil applied pesticides viz., metsulfuron methyl (Sulfonyl urea herbicide), atrazine (Triazine herbicide), carbendazim (Benzimidazole fungicide) and chlorpyriphos (Organo phosphorus insecticide) using the following methods. One g of the soil sample was taken in a centrifuge tube and the respective pesticide at 20, 40, 60, 80 and 100 ppm were added followed by 25 ml of water. The soil samples were shaken for 16 hours and centrifuged at 5000 rpm for 5 minutes. The supernatant liquid was removed and the samples were extracted and the residues were determined using standard procedures. The final determination was carried out by HPLC for metsulfuron methyl, atrazine and carbendazim and GC for chlorpyriphos. The desorption studies were carried out from the residual soil using 0.01 M CaCl2. The movement of soil applied pesticides was conducted using pesticide leaching apparatus. The degradation and persistence studies were conducted after the application of pesticide in 50g soil kept in polythene containers. The soil samples were maintained at field capacity moisture under controlled conditions. The soil samples were collected at 0 (1 hr.), 1, 3, 5, 10, 15, 30, 45 and 60 days after applications and analysed for pesticide residues using above methods. The results revealed that the adsorption was the highest in black soil irrespective of the pesticides tried. Among the pesticides, atrazine was adsorbed more followed by chlorpyriphos, carbendazim and metsulfuran methyl. The desorption studies revealed that red soil desorbed more amount of pesticides followed by alluvial, laterite and black soil. Atrazine retained in the top soil (0-10 cm) at the highest level followed by chlorpyriphos, carbendazim and metsulfuran methyl. The mobility of metsulfuran methyl was higher irrespective of soil types. Among the soil types red soil registered the highest mobility of all the pesticides. The soil applied pesticides in general followed 1st order kinetics and RF 1st order depending upon the soil types. In general, all the four pesticides recorded higher persistence in black soil and lower half life in red soil.