Spontaneous plant species in agricultural areas have been regarded as weeds, invasive or unwanted plants, when considering the damages that they can bring to cultivated species. However, spontaneous species can bring about the same effects of soil protection and nutrient cycling that cultivated or introduced species used for green manure do. Biomass productivity and nutrient accumulation for the aerial part of spontaneous and leguminous plants used as green fertilizers were measured at the experimental station Embrapa Corn and Sorghum, in Sete Lagoas, Minas Gerais (Brazil). The experiment comprised five leguminous species (Canavalia ensiformes, Canavalia brasiliensis, Mucuna aterrima, dolichos lablab and Cajanus cajan) tested in two growing conditions (with and without weeding), and a control (only spontaneous species). At flowering of the leguminous species, dry matter and nutrient level of the aerial part, for each leguminous and spontaneous species present in the parcels, were obtained. The system which had only spontaneous species produced less biomass and accumulated less nutrient than the systems with leguminous species. Few spontaneous species presented carbon, calcium and nitrogen levels which were close to or larger than the leguminous one. However, the inverse occurred for potassium, magnesium and phosphorus. Most spontaneous species presented potassium and magnesium levels, and several of them, phosphorus levels , larger than the leguminous ones. With regard to levels of phosphorus, potassium and magnesium, the following spontaneous species stood out: Portulaca oleracea, Euphorbia heterophylla, Bidens pilosa, Commelina benghalensis and Melanpodium perfoliatum.
biomass productivity; nutrient cycling; invasive