Root interactions between intercropped legumes and non-legumes-a competition study of red clover and red beet at different nitrogen levels

摘要

To investigate root competition in a legumeon-legume mixture, and how root growth of the legume is affected by the competition at increasing nitrogen (N) supply. Red beet (Beta vulgaris L.) and red clover (Trifolium pratense L.) were grown in transparent rhizotron tubes either in mixture or as sole crop at N supplies of 0, 75 or 150 kg ha(-1). The root growth was evaluated by the root intensity on the rhizotron surface, root depth and plant uptake of N-15 injected into the soil at the deeper part of the red clover root system. Competition with red beet decreased clover root intensity in deeper soil layers compared to clover grown as sole crop. The difference between clover in sole crop and in mixture was not evident at the highest N supply because the root growth of clover in sole crop appeared to be lowered at high N level. Increased N supply increased the dominance of red beet, but generally did not alter the root growth and distribution of the two species grown in mixture. Clover root growth and rooting depth were inhibited by competition with red beet but the effect was not enhanced by increased N supply; hence the increased dominance of red beet at higher N level was likely due to its increased growth and competitiveness for other soil resources.