Effect of continuous direct seeding on weed species diversity in Seberang Perai rice granary, Malaysia

M. Azmi and M. Mashhor

Abstract

Weed surveys were conducted in nine consecutive seasons at Seberang Perai, Malaysia between January 1990 and October 1994. The dominant weed species between seasons were compared using importance value. A total of 48 weed species belonging to 22 families under 36 genera were recorded. Of these, 23 species were broad-leaved weeds, 12 grasses, 9 sedges and 4 submerged weeds were recorded. Two to four of the species were dominant with less than 30 marginal species each season. Echinochloa crus-galli var. formosensis and Leptochloa chinensis were ubiquitous, dominant and competitive weeds in all seasons. The rating of dominant species was Monochoria vaginalis, Bacopa rotundifolia and E. crus-galli during the off-season 1990; M. vaginalis and E. crus-galli during the main season 1990/91; Leptochloa chinensis, M. vaginalis and E. crus-galli during the off season 1991; L. chinensis, E. crus-galli and Fimbristylis miliacea during the main season 1991/92; B. rotundifolia, M. vaginalis, E. crus-galli and L. chinensis during the off-season 1992; L. chinensis and E. crus-galli during the main season 1992/93; L. chinensis, E. crusgalli and B. rotundofolia during the off season 1993; L. chinensis, E. crus-galli, S. guyanensis and Najas graminea during the main season 1993/94; B. rotundifolia, L. chinensis and S. grossus during the off season 1994. Weed species diversity based on Sorenson's index of similarity indicated that at least 38% of the listed species occurred in all seasons.

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