Presentation on theme: "Persistence and Degradation of Herbicides in Rice, Maize and Soybean Grown in Vertisols of Tamil Nadu, Southern India P. JANAKI Herbicide Residue Chemist."— Presentation transcript:
1Persistence and Degradation of Herbicides in Rice, Maize and Soybean Grown in Vertisols of Tamil Nadu, Southern IndiaP. JANAKIHerbicide Residue ChemistDWSR Centre, Department of Agronomy,Tamil Nadu Agricultural University, Coimbatore ,Tamil Nadu, India
11Experimental Details Soil Properties Rice soil Maize soil Soybean soil Soil typeClay loamSandy Clay loamOrganic Carbon (g kg-1)3.92.303.00Available N (kg ha-1)314137190Available P (kg ha-1)15.249.011.20Available K (kg ha-1)796904642Infiltration rate (cm hr-1)1.681.591.52Bulk Density (g cm-3)1.231.321.33Porosity (%)424648
12Treatments and methodology CropsHerbicidesDosesDeterminationRecovery (%)RiceButachlorX (1 kg ha-1)2X (2 kg ha-1)GC-ECD86-88Pretilachlor82-84MaizeAtrazineGC-FID78-83AlachlorX (0.75 kg ha-1)2X (1.50 kg ha-1)> 80SoybeanPendimethalin81-82Metolachlor
15Field dissipation of applied herbicides in vertisols
16Half-lifeHerbicides persistence in the soil is expressed as half life or time required for degradation of fifty percent of the original molecule.The persistence varies with the nature of a chemical, soil and climatic conditions.
17Persistence in Rice grown soil Sampling intervals after herbicide application (Days)Butachlor Residue (mg kg-1)x (1 kg/ha)2 x (2 kg/ha)0.3280.658100.1940.300200.0070.02030BDL0.0054590HarvestSampling intervals after herbicide application (Days)Pretilachlor Residue (mg kg-1)x (1 kg/ha)2 x (2 kg/ha)0.2140.486150.0960.246300.0580.189450.02060BDL0.01490Harvest
24Summary Initial deposits vary with the concentration applied Gradual and continuous dissipation was observed as a function of timeDissipation followed the first order kineticsHalf life increased with increase in concentrationMean half life of herbicides : 5.88, 12.44, 31.45, 4.78, and days for butachlor, pretilachlor, atrazine, alachlor, pendimethalin and metolachlor