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Ecological Considerations in the Selection of Leguminous Plants as Cover Crops on The Vertisols of the Accra Plains in Ghana
Experiments were conducted in 2003 and 2004 to select leguminous cover crops for the Accra plains ecology in Ghana, based on the ability to withstand drought, produce enough biomass and fix nitrogen. In a randomised complete block design, Crotalaria ochroleuca, Stylosanthes ha-mata, Stylosanthes guianensis, Aeschenomene histrix, Chamaecrista rotundifolia, Sesbania ses-ban and Leucena leucocephala were grown and plant residues incorporated into the soil. Other treatments were recommended inorganic fertilizer application and no fertilization (control). Maize was planted on all plots and data collected on biomass of leguminous residues and also shoot biomass, cob weight and grain yield of maize. Soil samples were taken and analysed for pH, organic carbon and nitrogen (N). The leguminous plant materials were also analysed for N, phosphorus (P) and potassium (K). Annual rainfalls of 2003 and 2004 were low and dry matter yields of some leguminous plants (e.g. Aeschenomene histrix and Chamaecrista rotundifolia) were consequently low. Also, Crotalaria ochroleuca, Leucena leucocephala, Sesbania sesban and Chamaecrista rotundifolia had higher percentage of N per unit dry weight than the other leguminous plants (3.1, 3.1, 2.8 and 2.8, respectively). In the major rainy season of 2004, maize after Sesbania sesban had higher total dry matter, cob weight and grain yield than observed in the unfertilized control and were comparable to those of the inorganic fertilizer application. Grain yields were 2.4, 0.9 and 3.5 t ha-1, respectively. In the minor season, crop growth and yield were much lower in all the treatments due to low rainfall. By virtue of its high vegetative growth and nitrogen fixation, Sesbania sesban was selected as suitable cover crop for the Accra plains.