Nicandra physalodes (L.) Gaertn. is a weed that frequently infests Brazilian agricultural areas. Knowledge of the plant's response to competition, in the form of nutrient availability in soil, is fundamental to management of agroecosystems. This study aimed to evaluate the effect of concentrations of N, P and K on the growth of N. physalodes. The experiment was carried out in greenhouse conditions, using a randomized complete block design with split-plot arrangement (4 x 10), with three replications. The main plots were four combinations of N, P and K: (L1) 26, 33, 40, 47, 54, 61, 76, 91, 106 and 121 days after emergence (DAE). The dry matter, dry matter partitioning, leaf area, relative growth rate, height and photochemical efficiency of photosystem II were measured in N. physalodes plants at each harvest time. Overall, the leaves showed higher total dry matter accumulation up to 61 DAE. After that, the reproductive organs showed higher accumulation. Increasing concentrations of N, P and K resulted in higher plant height and dry matter of N. physalodes. Moreover, doubling the nutrient levels resulted in a proportional increase in dry matter accumulation. However, N. physalodes showed lower growth under natural soil fertility conditions (L1 treatment). Thus, increasing concentrations of N, P, and K promoted higher growth of N. physalodes. Biomass distribution was not changed by fertilization. There is evidence that N. physalodes could adapt easily in fertile soil. Thus, this species has greater competitive potential in high fertility soils.
