We investigated the chemical and biochemical composition, residue decomposition, and mineralization rate of leguminous (Cajanus cajan, Crotalaria spectabilis, and Lablab purpureus) and spontaneous vegetation in two experimental coffee systems in southeast Brazil. The nitrogen (N) content of the shoot biomass varied from 19.3 to 45.7 g kg-1, and phosphorus (P) content ranged from 1.6 to 3.8 g kg-1. C. cajan contained the greatest values of N and P, whereas spontaneous plants had the lowest values. In both areas, spontaneous vegetation had the greatest values of carbon (C) / P, C/N, polyphenol/N, and (lignin + polyphenol) / N ratios. Decomposition rate increased in the order C. cajan C. spectabilis L. purpureus spontaneous vegetation. There was no correlation between the chemical and biochemical composition and the decomposition rate under field conditions. However, the cumulative carbon dioxide (C-CO2) produced by the residues under laboratory conditions was correlated positively with initial contents of N and P and negatively with polyphenol/N and (lignin + polyphenol) / N ratio (P 0.01) throughout the sampling period. The low nutrient content, especially for N, of spontaneous vegetation is compensated by the greater decomposition rate under natural conditions than that of introduced species. Management of the spontaneous plants is therefore an attractive alternative for sustainable agriculture.
