Abstract-Tropical soils have low fertility and chemical fertilizers are not affordable for most of the farmers, especially in West Africa. The development of low cost technologies for amending agricultural soils in this environment is needed. Biological and organic fertilizers were tested in 20 farmers' fields in central Benin for rainfed rice production on acidic plinthosol under monomodal rainfall pattern conditions. Short time matured cowpea and native grass fallow were preceding NERICA1 and Ina Okpè rice cultivars that are interspecific (Oryza glaberrima × Oryza sativa) and local varieties respectively. Cowpea and bush residues were incorporated into soil before rice seeding. Soil nutrients (C,N,K, Ca and Zn) contents were significantly depleted whereas null balance was observed for soil available-P content. An increased of soil content in Fe (>130 mg kg -1 ) was significantly observed in all the treatments. Highest yield of 1.6 t ha -1 was recorded in the treatment composed of cowpea and NERICA1. The study technology was deemed suitable in deficient-P acid soil whereas the land foot slope position was excluded to avoid potential increasing of Fe content (iron toxicity of rice) in soil of the subsequent lowland. Minimum chemical fertilizer was required for improving rainfed rice cultivation on plinthosol in monomodal rainfall pattern ecology.