Phytotoxic effects of Centrosema pubescens and Calopogonium caeruleum litter on seed germination and seedling growth of Asystasia gangetica and Pennisetum polystachion

To evaluate the Allelopathic effect of residue extracts of C. pubescens and C. caeruleum on A. gangetica and P. polystachion, two greenhouse and laboratory experiment were carried out at Putra University, Malaysia, in 2012. In laboratory experiment, the litter leachates of C. pubescens sicnificantly reduced seed germination (%) of both weeds, but C. caeruleum had no significant effect on seed germination of both weeds. However, both cover crops increased seed germination time – length of both weeds. Residue extracts of both cover crops reduced hypocotyl length of A. gangetica and inhibitory effect of C. caeruleum was higher than C. pubescens. However, in pot culture, the increased concentration of both cover crop extracts incorporated with soil did not affect root and shoot length, dry weight and chlorophyll content of both weed seedlings. The results of residue decomposition of these two cover crops in soil showed that phenolic compounds are not persistent in soil. The results of this experiment also showed that the Allelopathic effect of both cover crops on seed germination and seedling growth depended on weed species, and residues of both cover crops in mixture with soil did not affect the seedling growth of both weed species