Atrazine is the most important triazine herbicides with moderately persistence in soil. The objective of this investigation was to study the degradation of atrazine (50 ppm) in two soils different in texture. Experiment was conducted in completely randomized design with factorial arrangement and 3 replications. Experimental factors included, soil texture (sandy loam and silty clay) and organic manure (0, 2 and 5 percent(w/w)). Soil samples were incubated at 30 oC and dark conditions for 0, 20, 40 and 60 days. At the end of each incubation period, atrazine residue was measured with HPLC. Data was fitted to first order kinetic equation for analysis. Results showed that soil texture and organic manure had significant effects on atrazine degradation rate. Atrazine degradation rate in clay soil with no organic amendment was 1.54 times higher than sandy soil and its half life were 138.6 and 90 days in two soil respectively. Atrazine degradation coefficient increased by 1.14 , 1.8 times in sandy loam soil and by 1.54 , 2.46 times in silty clay soil with 2 percent and 5 percent organic amendment, and the half-life decreased from 138.6, days to 121.57 and 77 days in sandy soil and from 90, days to 58.22 and 38 days in clay soil. It seems that atrazine degredation in silty clay soil is more than sandy loam soil and soil organic manure have an important role in atrazine bioremediation.

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