Aiming to study the effect of the application of increasing levels of phosphorus on some parameters of growing of plants of Sorghum bicolor (L.) Moench (sorghum) and Cyperus rotundus L., grow isolated or in community, an experiment was conducted in pots. A soil colleted at the arable layer of dark red latossol median texture was used for filling the pots. The experimental desing was a of completely randomized with 5 replication. The treatments were arranged at a 3 x 6 factorial plot where the variables were: three conditions of vegetation at the pots (3 sorghum plants per pot; population originally from the insertion of four tubers of Cyperus rotundus per pot; and three plants of sorghum in community with plants originally from four tubers of C. rotundus per pots) and six levels of phosphorus aplications (0, 25, 50, 100, 150 and 200 mg/kg of P/pot). The experiment lasted for fifty days. For the data statistical analysis it was considered within each specie a factorial of 2 x 6 that is two conditions (isolated or in community) and six levels of P applications. It was observed that both species showed an increasing response in relation to the rates of P application. It was also noticed that there was an improvement of all studied characteristics, but this improvement occurred in lower levels when both kinds of plants were grown together. In this case, this increase only was significant until the rate of 100 mg/kg of P for Cyperus rotundus plants and 150 mg/kg of P for sorghum plants when both were grown separated. When they were grown together, sorghum plants had a significant response only from the rate of 50 mg/kg. It was in lower doses that purple nutsedge showed their competitive action, reducing significantly the leaf area and the accumulation of dry matter in leaves and stems of sorghum. Sorghum plants was more competitive when the higher doses of P were applied (150 and 200 mg/kg). This fact may be related to the capacity of shading of sorghum over the Cyperus rotundus. The presence of sorghum reduced the leaf area, number and accumulation of dry matter in sprouts and tubers of Cyperus rotundus. With the increase in the rate of application of fertilizer with phosphorus, Cyperus rotundus showed a greater allocation of dry matter in the aerial part than in the tubers.
competition; phosphorus; Cyperus rotundus; Sorghum bicolor