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Predicted density (plants m –2 )5040Lindernia spp.Ammannia baccifera302010Echinochloa colonaLeptochloachinensisFimbristylis miliaceaCyperus difformis0–2 –1 0 1 2 Axis 1Site distributionLowerMiddleUpperFig. 6. Log-linear regression of density of selected species per quadraton the site scores of the first axis of correspondence analysis(Fig. 5) assuming a Gaussian distribution function. Axis scores themselveswere derived from the site ordination and are not those shownin Figure 5, which have been rescaled for biplot presentation. Regressionsgave significant (P ≤ 0.05) fits to abundance distributionsfor all species except Ammannia baccifera.were found in lower toposequence positions with differences of up to 1 t ha –1 beingrecorded. Average on-farm yields in the same locality, however, have been reportedto be significantly lower and typically less than 3 t ha –1 (Syamsiah et al 1994).While confirming the well-known variability in soil characteristics in Java, thisstudy illustrates that surprisingly dense, diverse weed communities persisted ingogorancah rice during the latter stages of crop development. Within the restrictionsof this study and by inference only, these may be strongly structured by spatial variabilityin soil pH, by nutrient availability governed by soil pH, and by hydrologythrough toposequence position. The literature is sparse on data describing speciesdistributional ranges in relation to soil characteristics in Indonesia. It is interesting tonote, however, that Echinochloa crus-galli achieved a mid score on axis 1 (Fig. 7)and that this species is reported to prefer neutral soils (Soerjani et al 1987). Figure 3indicates that only seven species were common (>5%) in the upper and midtoposequence with five in the lower toposequence. Acidic, nutrient-poor sites in theupper toposequence were dominated by Lindernia spp., which are commonly consideredto be ruderal species of open sites. Habitat specificity was reflected within Cyperus,with C. tenuispica being replaced by C. difformis in lower site locations, whereWeed communities of gogorancah rice and reflections on management 281