Research and Development Note: The utilization of Azolla as a source of nitrogen for rice production in Ghana

Abstract

The performance of the local strain of Azolla, Azolla pinnata var. africana, as a green manure for rice was compared with inorganic nitrogen alone and a combination of Azolla and inorganic nitrogen. The Azolla was incorporated under the rice crop (cv. GRUG 7) grown under irrigation on the vertisol. Within a period of 4 weeks and a doubling time of 5 days, a total biomass of 18 t/ha of Azolla, equivalent to 25 kg N/ha was produced. This is 28 per cent of the optimum recommended nitrogen rate (90 kg N/ha) for rice cultivation on the vertisols of the Accra Plains. Azolla, in combination with 40 kg N/ha ammonium sulphate fertilizer, gave significantly higher grain yields than Azolla only, 60 kg N/ha ammonium sulphate fertilizer and the control plot. No significant grain yield differences were observed between the single and double Azolla incorporations, but the double incorporation of Azolla only gave a yield equivalent to that obtained under 60 kg N/ha ammonium sulphate while a lower yield was observed for the single incorporation. The grain yields were 4.8, 3.5, 2.7 and 1.8 t/ha for the Azolla plus N-fertilizer, 60 kg N/ha, Azolla only and the control plot respeectively.


(Ghana Journal of Agricultural Science, 1996, 29(2): 125-129)