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 future weed control strategies. This study designed to address quantitative effects on weed ecology as a result of changing water regime, tillage intensity and herbicide dose, was carried out on a farmers field in village Baluga, Talavera, Nueva Ecija, located in central Luzon, Philippines. The treatments included: three water regimes, viz., Shallow continuous pending throughout the crop growth, pending until panicle initiation and then saturated soil, and saturated soil throughout, two tillage intensities, viz, one plowing + 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 panicle initiation reduced weed species number, density and biomass as compared 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 were equally effective in reducing the number, density and biomass of different species, but no herbicide treatment encouraged almost all species to grow. Cyperus difformis L. was the most dominant species during both the wet and dry seasons followed by Ammannia baccifera L. during the dry season, and Ammannia baccifera L., Paspalum distichum L. and Sphenoclea zeylanica Gaertn. during wet season. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.