INTER-SPECIFIC AND INTRASPECIFIC COMPETITION OF FAT-HEN (CHENOPODIUM-ALBUM L) AND GROUNDSEL (SENECIO-VULGARIS L)

The responses of Chenopodium album L. and Senecio vulgaris L. to inter - and intra-specific competition were investigated in both additive an d replacement series experiments under glasshouse conditions. When gro wn with tomato the two weed species had similar effects on shoot dry w eight at low densities but S. vulgaris showed more competitive effect at higher densities. Weed density did not affect the concentrations of N, P, K, Ca or Mg in tomato shoots but dry matter and total amounts o f nutrients were reduced increasingly with the increase in density of both weeds. The concentration of nutrients in the shoots of the weeds was not affected by density but dry matter yield and total nutrient ac cumulation per plant fell as the density increased. The concentrations of N, P, K and Mg in the shoots were higher in C. album than S. vulga ris but that of Ca was lower. In a replacement series experiment the t wo weed species behaved differently. With C. album, both dry matter yi eld and total nutrient per plant were reduced as its proportion in the mixture increased but, with S. vulgaris, dry matter per plant increas ed with its proportion in the mixture. One plant of C. album grown wit h five S. vulgaris gave a higher shoot dry weight than when present in higher proportions or in a pure stand. In a pure stand of six plants the shoot dry weight per plant of C album was 26% of that of one plant grown with five S. vulgaris. In comparison, the shoot dry weight of o ne S. vulgaris in pure stand was 120% of that of one plant grown with five C album. The reduction in growth of C album was associated with a greater reduction in its ability to accumulate K than other elements. The competition index (CI) of C. album in terms of dry weight decreas ed with its proportion in the mixture but the reverse was true for S. vulgaris. The relative competitive ability index (RCAI) of C. album wa s almost 3.5 times that of S. vulgaris. The results showed that differ ences between the weeds in inter- and intraspecific competition were c losely related to the growth of their root systems.