LONG TERM HERBICIDAL WEED MANAGEMENT INTEGRATED WITH NITROGEN NUTRIENT IN TRANSPLANTED RICE-RICE CROPPING SYSTEM OF TAMIL NADU, INDIA

With a primary objective to evaluate the long-term herbicide application integrated with nitrogen management on weed shift, weed control efficiency, soil micro flora, herbicide residue and productivity of transplanted rice-rice cropping system, field experiments were conducted for ten years from 2000 to 2010. Field experiments with hand weeding (HW) twice, pre-emergence butachlor 0.75 or pretilachlor 0.75 kg/ha or in rotation + post emergence 2,4, D, 0.4 kg/ha along with inorganic and organic nitrogen(N) at 75 and 25 percent were conducted with four replications arranged in a randomized blocks design. Decreased grass weeds density from 53.0% with first rice crop during kharif 2000 to 42.1% with eighteenth rice in HW with 100% N as inorganics, was observed. Broad leaved weed (BLW) density was higher with HW in eighteenth and nineteenth rice crops compared to first rice crop. Ludwigia parviflora, Eclipta alba and Marselia quadrifoliata were BLWs in nineteenth and twentieth rice crops. Weed shift from Echinochloa crusgalli to Panicum distachyon was observed, which was more in rotational use of herbicides. BLW density was higher in HW with nineteenth and twentieth rice crops compared to first crop. Reduced weed density and dry weight were observed with herbicidal weed control and it was well pronounced under rotational use of herbicides (butachlor in kharif and pretilachlor in rabi with 2,4-D). Herbicides application recorded significantly higher yield in nineteenth and twentieth rice crops and the yield increase was higher with continuous and rotational use of herbicides. Residues of butachlor, pretilachlor and 2,4-D were below deductable level from 45 days after application in soil and crop. Improvement in soil actinomycetes, fungi and bacteria was observed with herbicides application.