Campuloclinium macrocephalum is an Asteraceous alien weed that invades roadside vegetation and grassland in South Africa. The role of allelopathy and competition in its invasiveness was investigated using Eragrostis curvula (weeping lovegrass, an indigenous grass), E. tef and Lactuca sativa (lettuce) as test species. Trials were conducted in Petri-dishes, pots and in the field. Root and shoot extracts of adult C. macrocephalum plants did not inhibit seed germination in any test species. The greatest effect was radicle stunting produced by leaf extracts at 10 and 25% w/v. Eragrostis curvula was less tolerant of the extracts than E. tef. Allelopathic effects could however not be confirmed in pot trials evaluating the interference potential of the weed or weed residue effects against E. curvula. E. curvula growth and biomass was not affected by plant densities of one or five C. macrocephalum per pot, whereas C. macrocephalum suffered a 17% mortality and density-dependant trade-offs of size and biomass for survival. Under field conditions C. macrocephalum had a broader ecological niche than E. curvula, invading hygrophilous and undisturbed grasslands not amenable for E. curvula establishment, this included well drained disturbed soils on which the latter proliferated. Evidence of competitive exclusion of E. curvula by C. macrocephalum or vice versa was not detected. The coexistence of both species irrespective of relative density suggested these species have different resource requirements. Allelopathy was not an adequate causal mechanism to explain invasiveness in Campuloclinium macrocephalum. A more traditional hypothesis such as the absence of natural enemies, at this stage, better justifies the weed's invasion success.

Nematodes play an important role in agricultural soil in terms of their pest status and their contribution to soil quality, where they may serve as a valuable indicator of soil health. The aim of the study was to assess changes occurring in nematode community structure, as affected by soil tillage applied to high N-input and irrigated pastures in South Africa. Such practices were investigated by means of analysing diversity and ecosystem function indices, as well as the faunal profile, to enable analysis of their effect on soil quality. The pre-treatment soil analyses showed a low overall mean nematode density. No clear and predictable pattern was present in the nematode community structure in relation to tillage. The lack of indicative information leading from the nematode community structure to the tillage disturbance types might be linked to the fact that such systems were able to recover from soil disturbance within the relatively short period of less than a year.

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