Seedbank and Seedling Emergence Characteristics of Weeds in Ricefield Soils of the Muda Granary Area in North-West Peninsular Malaysia

Abstract

Tlie experiment was conducted in the glasshouse of UPM from March 2003 to June 2004 to determine the soil seedbank in the ricefields ot'Muda rice granary area in Peninsular Malaysia. Six soil cores of 5 cm in diameter and 10 cm depth were sampled from each of 24 fields. All samples from each individual field were bulked and placed in plastic trays of 38 x 25 x 10 cm. Soil was moistened as required and emergence of weed seedlings were recorded over period of one year. After one year, remaining seeds were separated, removed and identified. The total seed bank was estimated at 1136.48 million/ha of which 62.35% (708.60 million seedlings ha" 1) germinated within 12 months and 37.65% (427.88 million seeds ha" 1) remained ungerminated. Total of 20 taxa were recognized. Based on importance value (I.V.) the five most dominant species in terms of emerged seedling were Fimbristylis miliacea, Leplochloa chinensis, LitJwigia hyssopifolia, Cyperus difformii and C. iria. Of the remaining seeds the five dominant species with decreasing trend in ranking were F. miliacea, Scirpus lateriflonis, Monochoria vagina/is, L. hyssopifolia and L. chinensis. Ranking of total seed reserves (seedlings+ remaining seeds) were similar to emerged seedling indicating that emerged seedlings reflect the actual weed flora in the Muda area. Among the dominant species F. miliacea accounted for 58.07% of emerged seedlings, 79.31% of remaining seeds and 66.07% of total seed bank. Total seedling emergence of all species was higher in the first observation in April 2003 and cumulative seedling emergence showed no clear peaks.

Continuous Practice of Conservation Agriculture for 3–5 Years in Intensive Rice-Based Cropping Patterns Reduces Soil Weed Seedbank

“…Fewer aboveground weed taxa in 50% residue than 20% residue might be due to the effective suppression of germinated weeds, caused by the physical barrier of extra residue, lower soil temperatures, and allelochemicals released from decaying plant tissues in the field, as suggested by [29]. Moreover, reduced light penetration and cooler average soil temperatures in 50% residue, relative to 20% residue, could reduce weed seed germination or delay germination, damage of weed seeds, due to predation, and decomposition by macro and microbial populations [30]; delay emergence of etiolated plants that, in turn, produced fewer seeds, as stated earlier [31]. Comparatively higher and lower values of qualitative and quantitative similarity indices, respectively, in 50% residue than 20% signify a more diversified weed seedbank in the 50% residue than the 20% residue in this study.…”