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Utilization of Azolla as manure in lowland rice cultivation on the vertisols of the Accra plains of Ghana
On-farm studies were carried out in order to impart to farmers techniques of using azolla in lowland rice cultivation on the Vertisol. The experiments were conducted on four farms at the Kpong Irrigation Project sites, at Akuse and Asutsuare, from 2002 to 2006. The design of experiment was randomised complete block, with five treatments and four replications. Azolla was grown in designated rice basins (3m x 4 m) for 6 weeks and water drained three days before transplanting rice. Azolla was also grown in external basins and added to give total of 25 t ha-1 fresh weight (1.2 t ha-1 dry weight). As rice was transplanted, azolla was trampled and thus incorporated into the soil. The treatments included: Incorporated azolla only (A1), azolla + 15:15:15 NPK compound fertilizer application (A2), azolla + 15:15:15 NPK fertilizer + ½ sulphate of ammonia fertilizer (A3), application of recommended 15:15:15 NPK fertilizer + sulphate of ammonia (F) and no azolla or inorganic fertilizer application - control (N). Data on the rice crop included: plant height, tillers per plant, total dry weight at booting stage and grain yield at maturity. Soils were sampled at the end of experiments and analysed for pH, nitrogen and organic carbon. The nitrogen content of incorporated azolla was 2.2 %, giving a nitrogen equiva-lent of 27 kg ha-1. Azolla plus 15:15:15 NPK fertilizer gave a yield of 5.3 t ha-1 paddy (A2) that was comparable to that of the recommended inorganic fertilizer applications (F) - 5.1 t ha-1 and greater than the control (N) - 2.9 t ha-1. In Hammond’s farm, where azolla was incorporated over a period of three years, rice yield was higher than observed in Moses’ farm, where azolla incorporation was for one year only. Cost-benefit analysis indicated a 20.7 % savings on fertilizer application.