Field pea (Pisum sativum L.) and blue lupin (Lupinus angustifolius L.) were either sole cropped or inter-cropped with barley (Hordeum vulgare L.) at two levels of nitrogen application to determine the effects of interspecific interaction in an intercrop and nitro-gen fertility on competitive ability towards volunteer crops - exemplified by red clover (Trifolium pratense). The dynamically change of competitive ability by intercropped species over time was shown to be im-portant in order to reduce opportunities for growth of volunteer crops and weed
