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Table 2. Correlation (product moment) matrix of soil characteristicspooled over sites and toposequence position. Data in bold are significant(P ≤ 0.05). CEC = cation exchange capacity.pH C N P KC 0.7252N 0.5723 0.6151P –0.2343 –0.2572 –0.2871K 0.4421 0.3680 0.2719 –0.1623CEC 0.6982 0.6778 0.5222 –0.2636 0.6190Weed abundanceFifty-six weed species (Table 3) in total from 18 familes (Amaranthaceae, Araceae,Asteraceae, Boraginaceae, Commelinaceae, Convolvulaceae, Cyperaceae,Euphorbiaceae, Lythraceae, Marsileaceae, Molluginaceae, Onagraceae, Poaceae,Pontederiaceae, Portulacaceae, Rubiaceae, Sphenocleaceae, Scrophulariaceae) wererecorded in the census. The developmental stages of species varied considerably, mostbeing vegetative and below the crop canopy height. Species commonly observed inthe flowering stage were Eclipta alba, Echinochloa crus-galli, E. colona, Fimbristylismiliacea, and Cyperus difformis and C. rotundus.The overall mean total weed density was 175 plants m –2 (Fig. 1) and this did notdiffer significantly in relation to toposequence when averaged across sites. Positionswere ordered lower < middle < upper in terms of mean number of species. At lowpositions, the variance in densities was least and density distributions were highlyskewed in the mid and upper regions. Very high densities (above 400 plants m –2 )were always dominated by a single species. Frequency distribution of counts per m 2varied among species and between toposequence positions, both Poisson and lognormaldistributions being evident in the data set. For the most abundant species,distributions were typically strongly skewed but in some instances apparently disjunct(e.g., Ammannia baccifera, lower toposequence) (Fig. 2).Figure 3 illustrates the rank order abundance of species in each toposequence,based on pooled counts across sites. While all communities were structured geometrically,common taxa had a different rank in their relative abundance in relation totoposequence (Spearman’s R s , P ≤0.03). In the upper and mid toposequence, communitieswere dominated by a similar group of species with Lindernia spp. the mostabundant. At the low toposequence, Lindernia was replaced by Ammannia bacciferaand in low and mid positions Leptochloa chinensis was more abundant than in theupper toposequence. Both Echinochloa colona and Fimbristylis miliacea achievedhigh rankings across all toposequence positions. Ranking species by summed dominanceratio (averaged relative abundance and relative frequency) promoted relativelyrare species overall (e.g., Phyllanthus niruri and Digitaria ciliaris) to a much higherrank (Fig. 4), especially evident at the low toposequence.Figure 5 shows the biplot ordination from CA of species and sites according totoposequence. In the analysis, data were logarithmically transformed and the influ-Weed communities of gogorancah rice and reflections on management 275