Effect of Source of Organic Matter on the Persistence of Butachlor and Pretilachlor in a Lateritic Soil under Flooded Soil Conditions

The influence of source of organic matter on the dissipation of two chloroacetamide herbicides butachlor and pretilachlor, in a lateritic soil under flooded condition is reported. Two exogenous sources of organic matter viz., farm yard manure (FYM) and vermicompost, and soil alone (control) were taken as treatments under each herbicide. The soil was kept under submerged condition in mud pots by maintaining 3 cm water above the soil surface. The herbicides, butachlor and pretilachlor were applied @ 1.25 and 0.45 kg ai ha⁻¹ respectively and each manure @ 5.0 t ha ⁻¹. The results showed that butachlor as well as pretilachlor with FYM dissipated slowly compared to soil alone and vermicompost. At one day after application of herbicides, significant variation in the dissolved organic carbon (DOC) content was noticed among the organic manure treatments. The initial concentration of residues in soil (1 day after spraying, DAS) was lowered by DOC released from the farmyard manure, However, total organic carbon content was significantly higher under FYM treatment up to four weeks after herbicide application. The half life of both the herbicides was also higher in FYM treatment as compared to vermicompost and control (soil alone). The results indicated superiority of FYM in retaining the herbicides for longer period of weed control in rice.