Assessment of the allelopathic effects of seeds and seedlings of rotational crops and ryegrass

Allelopathic effects were evaluated for a series of rotational crops, namely barley, canola, wheat, lupine, medic, lucerne (alfalfa) and ryegrass in laboratory studies. This followed on a field assessment of these crops to identify inter-species phytotoxic effects. Two different experiments to determine phytotoxicity effects of seed and seedling leachates were conducted under controlled conditions. The first experiment was set up in the laboratory to observe the mutual effect of seed leachates from the plant series. The second experiment was conducted in the laboratory to study the effect of seedling leachates from all the plants in the series on germination and early development of all other species. The phytotoxic activity observed for lupine and medic under controlled conditions, corresponds to results obtained in the field and confirms that these leguminous crops could be considered as living or terminated mulches for weed suppression. Crop mixtures containing legumes may provide weed suppression which would reduce dependency on herbicides that are associated with the development of weed resistance.   Key words: Cumulative germination, inhibition, stimulation, phytotoxic leachates.