ABSTRACT
The objective of this study was to evaluate the productivity of shoot dry biomass and the capacity of nitrogen (N), phosphorus (P) and potassium (K) extraction by the Vetiver and Tifton 85 grasses when cultivated in horizontal subsurface flow constructed wetlands (HSSF-CWs) whose porous medium was saturated with solutions containing different nutrient availability. The grass shoots were cut every 30 days to determine the productivity and N, P and K contents in the plant tissue. Models of productivity and the extraction capacity of each nutrient were obtained as a function of the nutrient concentration. Based on the results obtained, it was verified that the productivity of shoot dry biomass and the extractions of N, P and K by the Vetiver grass increased linearly with the nutrient availability of the nutritive solution. In relation to Tifton 85, quadratic models of productivity and N and K extraction were adjusted. The maximum productivity, N, P and K extraction by Vetiver grass were 513.4, 8.2, 1.9 and 10.39 g m-2 month-1, respectively. In relation to Tifton 85 grass, these values were 739.4, 30.8, 3.0 and 15.59 g m-2 month-1 for productivity, N, P and K extraction, respectively.