Four green manure sources, viz., Mucuna pruriens (mucuna), Centrosema pubescence (centrosema), Pueraria phaseoloides (pueraria), and natural grass cover (dominated by Panicum maximum) and NPK fertilizer were evaluated for their comparative effects on four varieties of maize (FARZ23-Y, DMRSR-W, Hybrid-PAN 6195, and Bende White) in the forest zone of southeastern Nigeria, between 1999 and 2000. Mucuna gave significantly greater number of grains per cob and consequently higher grain yield in maize than the other green manure sources and NPK fertilizer, when the fallow period was maintained for two years. Pueraria-planted fallow always gave less grain yield, thus rendering it unsuitable for maize production. Var. FARZ23-Y gave significantly higher yield than the other varieties, and therefore, was more effective in exploiting the potential of the green manures.