Inter and intraspecific competition studies envolving Glycine max (L.) Merril and Cyperus rotundus L. were performed by measuring the effects on the growth and accumulation of N, P, K, Ca and Mg in the plants. The standard number of the plants per pot was three. In the interspecific competition plots three shoots of purple nutsedge and three plants of soybeans were cultivated per pot. In the intraspecific competition studies six shoots or plants per pot of C. rotundus or G. max were cultivated, respectively. The inter and intraspecific competitions response were different in these species. For purple nutsedge the effect of density was compensated by a larger shoot and tuber production in the low density treatment. In this last condition the tuber size was also larger. The interspecific competition showed a decisive effect of soybean shading on the C. rotundus behaviour. The nutrient competition showed different patterns for the different elements and species.
Glycine max; Cyperus rotundus; competition; mineral nutrition