Potential of Chromolaena odorata, Panicum maximum and Pueraria phaseoloides as nutrient sources and organic matter amendments for soil fertility maintenance in Ghana

The need to maintain soil organic matter in an effort to overcome declining soil fertility on smallholder farms in Ghana cannot be over emphasized. Wh ile organic matter such as poultry manure and cow dung are scarce, access t o inorganic fertilizers is limited due to high cost. Three high biomass-pro ducing plants (Chromolaena odorata, Panicum maximum and Pueraria phaseoloid es), considered as weeds on farmers' fields in Ghana, were evaluated as nut rient sources and organic matter amendments. Mass loss and nutrient release were measured from residues contained in litterbags buried 15 cm below the soil surface. Decomposition and nutrient release constants were estimated by fitting a single exponential model to the data. The initial resource qua lity analyses showed that the residues contained N and P levels that were h igher than the critical values below which net immobilization from the soil would be expected. Decomposition rates of the residues 56 days after buria l were not significantly different. All the plant residues had released mor e than 75% of their constituent elements at the end of the period. The half life of nutrient release of the residues suggest that they can be effectiv ely used together with or without a small amount of mineral fertilizer to p roduce maize, which is a major cereal in Ghana. Composts prepared from the plant residues were not significantly different in terms of their N, P, K, Ca and Na contents. The pH of all composts was near neutral making them sui table for application to any soil type. The plant residues or compost prepa red from them could therefore be used as sources of nutrients and soil orga nic matter amendment for increased crop production in Ghana.