Effect of Herbicides on Weed Control and Nitrogen Dynamics of Direct Sown Rice and Associated Weeds

A field experiment was conducted during Kharif 2002 and Rabi season 2002–03 on clay soil at the research farm of Directorate of Rice Research, with the objectives of determining the nitrogen harvesting by weeds and rice crop, working out the weed indices. The treatments were non-weeded check, hand weeding twice and 10 herbicides. It was found that grasses were dominant over sedges and broadleaved weeds. Dry matter production of weeds was minimum with butachlor+safener @ 1kg a.i. ha^-1, anilophos+ethoxysulfuron @ 0.312+0.012 kg a.i. ha^-1and butachlor+propanil @ 1.12+1.12 and 1.05+1.05 kg a.i. ha^-1indicating their effectiveness over the weed population. Treatments with butachlor+propanil @ 0.84+0.84 kg a.i. ha^-1, butachlor+safener @ 1kg a.i ha^-1recorded minimum nitrogen harvesting by weeds indicating their effectiveness, whereas anilophos+ethoxysulfuron @ 0.375+0.015 kg a.i. ha^-1, fenoxaprop-p-ethyl @ 0.056 kg a.i. ha^-1recorded higher nitrogen harvesting by weeds indicating their less effectiveness. Chemical weed control with butachlor+safener, butachlor+propanil @ 1.05+1.05, 1.12+1.12 kg a.i./ha at right time contributed to higher nitrogen harvesting and grain yield of rice and are promising in direct seeded rice under puddled conditions. Application of these herbicides controlled the weeds effectively and showed higher crop resistance and lower weed persistence.