The frequency, dominance, percentage of leaf cover and index of frequency x cover of annual and perennial species were evaluated, in areas dedicated to slash/mulch bean (frijol tapado) over 35-and 80- years periods with falIow periods forone and three years, in Guaitil of Acosta, Costa Rica. Soil nutrient available, their relationship with plant cover and foliar nutrient content of each especies were also evaluated. Under falIow periods of three years, perennial species were dominant. Under falIow periods of one year without pasturing, Rottboellia cochinchinensis was dominant, but, with pasturing, Sida rhombifolia predominated. Percentage of leaf cover of some species was well correlated with soil nutrient available, but its potential use as indicator of soil fertility was unclear. High nutrient levels in the foliage of some species suggests thepossibility to use weed species as a temporal storage of nutrient, eventualIy released back to the soil to be used by crop plants when the falIow is cut.