Weed Community Dynamics in the System of Rice Intensification (SRI) and the Efficacy of Mechanical Cultivation and Competitive Rice Cultivars for Weed Control in Indonesia

ABSTRACT The system of rice intensification (SRI) prescribes the use of young seedlings, planted at reduced densities and managed using reduced irrigation and frequent mechanical weeding, as a means of optimizing rice yields and reducing input costs. Such changes in management practice have been known to result in prominent shifts in weed flora, which if anticipated could help refine future weed control strategies. This study, conducted at four locations in West Java, Indonesia, examines the effects of two complimentary control tactics, mechanical cultivation and competitive rice cultivars, on individual weed species, broader weed classes and entire weed communities. Relative dry weights of individual weed species ranged widely from site-to-site. Differences in dry weight among weed classes were observed, with sedges accumulating greater biomass than either broadleaved weeds or grasses in nonweeded plots across all sites and cultivars. Mechanical cultivation was effective in reducing the dry weight, density, and species number of all weed classes. Effective weed control by mechanical cultivation also resulted in weed communities with lower species richness, greater dominance by fewer species, and hence lower overall diversity. The weed competitive cultivar (Sarinah) more effectively suppressed the dry weight of sedges and grasses than did the control variety (IR64), but had no influence on the dry weight of broadleaved weeds. Despite reducing total weed dry weight by 32%, use of a competitive cultivar had no effect on the density and species number of weed classes or any of the community-scale measures of diversity. Although competitive cultivars may have little effect on the relative abundance of resident weed species from an ecological standpoint, this should not diminish the practical potential such cultivars may have in reducing the number and intensity of weeding operations.