ABSTRACT In order to meet the need for nutrients or soil cover, when plants are used as green manure, it is necessary to determine the ideal plant population, as well as the amount and duration of released nutrients. This study aimed to assess the decomposition and nitrogen (N), phosphorus (P) and potassium (K) release rates of vetiver grass mulch. A split-plot arrangement was used, with the plots consisting of mulch decomposition times after cutting (0, 15, 25, 70 and 125 days) and the subplots of vetiver plant densities (1, 2, 3 and 4 plants m-2). A randomized block design was used, with four replications. The highest release rates for N, P and K were recorded during the first five days. The plant density of 3 plants m-2 exhibited the highest mulch dry weight at 125 days and contained more N, P and K, when compared to the populations of 1, 2 and 4 plants m-2.