Clover as a cover crop for weed suppression in an intercropping design - II. Competitive ability of several clover species

Undersown cover crop species introduced for weed management purposes should ideally combine adequate weed suppression with only marginal negative competitive effects on the main crop. The aim of this research was to identify the growth characteristics of clover species that determine weed suppressive ability and competitive ability against the main crop. In addition, the variation in these characteristics among clover species was determined, to identify whether species selection is an important component of the optimization of living mulch systems. In 2001, a field experiment was conducted in which weed suppression and competitive ability against leek of eight clover types was determined. Based on the results, three contrasting clover types were selected and their weed suppressive ability was further investigated in a field experiment conducted in 2002. Results of both experiments were related to growth characteristics that were simultaneously determined and described in a previous paper. Correlation analysis showed that the competitive effect of clover on transplanted leek was strongly correlated with maximum canopy height, indicating that yield reduction was mainly caused by competition for light. Subterranean clover, being the shortest species, gave inadequate weed suppression, whereas all other species were found to provide at least reasonable weed suppression. Subterranean clover reduced individual leek plant dry weight more strongly (60%) than expected based on its canopy height. Indications were found that this clover species was hindering the uptake of nitrogen by leek. Clover species with superior weed suppression, like Persian clover, red clover, alsike clover, berseem clover and crimson clover also gave the strongest negative effect on dry matter accumulation of leek (reductions between 70% and 90%). White clover was found to give the best compromise between adequate weed suppression and mild yield reduction, though also with this species reduction in leek plant dry weight was still 60%. It was concluded that for optimization of systems that introduce clover species as a weed suppressing cover crop species selection is important element, though additional management to restrict the competitive effect on the main crop remains a requirement. (c) 2006 Elsevier B.V. All rights reserved.