The mutual effect of ryegrass and clover when grown together

Italian ryegrass and a late-flowering red clover were grown together, with abundance of water and nutrients for both. It was found that even a small number of ryegrass plants reduced the growth of clover by 30%. This effect varied very little with increasing density of the clover crop. The presence of clover reduced the ryegrass crop by an amount diminishing as the density of the ryegrass was increased. In a sparse crop of ryegrass, clover reduced the growth of the grass considerably more than did barley under comparable conditions. There is no evidence of any specific effect of the roots of one plant on the other. When ample nitrogen is available the clover tends to take some that would otherwise be available for the grass and does not provide the grass with additional nitrogen.