Effect of water, tillage and herbicide on ecology of weed communities in intensive wet-seeded rice system

Quantitative information on shifts in weed flora brought about by changing soil and water management practices can provide valuable indications for fu ture weed control strategies. This study designed to address quantitative e ffects on weed ecology as a result of changing water regime, tillage intens ity and herbicide dose, was carried out on a farmers field in village Balug a, Talavera, Nueva Ecija, located in central Luzon, Philippines. The treatm ents included: three water regimes, viz., Shallow continuous pending throug hout the crop growth, pending until panicle initiation and then saturated s oil, and saturated soil throughout, two tillage intensities, viz, one plowi ng + two harrowings, and two plowings + two harrowings and three herbicide levels, viz. pretilachlor @ 0.30 kg a.i/ha, pretilachlor @ 0.15 kg a.i./ha, and no herbicide. Continuous shallow pending throughout as well as until p anicle initiation reduced weed species number, density and biomass as compa red to saturated soil throughout. In general, increase in tillage intensity did not produce significant effects on all the weed classes, but, sporadic reduction in some species was noticed. Full-and half-doses of herbicide we re equally effective in reducing the number, density and biomass of differe nt species, but no herbicide treatment encouraged almost all species to gro w. Cyperus difformis L. was the most dominant species during both the wet a nd dry seasons followed by Ammannia baccifera L. during the dry season, and Ammannia baccifera L., Paspalum distichum L. and Sphenoclea zeylanica Gaer tn. during wet season. (C) 1999 Published by Elsevier Science Ltd. All righ ts reserved.