Allelopathic effects of Cenchrus ciliaris L. and Bothriochloa pertusa (L.) A. camus

Cenchrus ciliaris l.,and bothriochloa pertusa (l) a. camus are perennial range grasses growing from plains upto 1000m in hot and dry tropical and subtropical regions of the world including pakistan. both these grasses are preferred for pasture due to easy germination,fast growth,good palatability and better productivity. however,the pasture generally declines after few years. the present study was conducted to see if allelopathy might be responsible for the declination of pastures. studies made with using aqueous extracts and added mulches from different plant parts indicated that extracts from various parts and mulches invariably inhibited the germination,radicle growth,dry weight and moisture contents of test species used in different bioassays and experiments. the toxicity depended upon the parts assayed,test species used,soaking duration and physiological parameter. above ground parts,especially leaves,were more toxic than roots. the toxicity enhanced with increasing soaking duration and amount of plant material. however,the toxicity of shoots declined with constant leaching of plant material. shoot mulches added to soil retarded the germination and dry weight of test species. it was observed that allelopathy operates through water soluble toxins. however,further study is needed to see the role of root exudates,rains leachates and to identify phytotoxins.