Response to different rates of nitrogen by five varieties of swamp rice (Orza sativa linn) under the tropical wetland conditions of Ini, Akwa Ibom state, Nigeria
A field experiment was conducted in 2011 and 2012 in Ini Local Government Area of Akwa Ibom State, Nigeria; mainly to determine the optimum nitrogen fertilizer rate for the area as well as select the rice varieties that responded optimally. A split plot design was used with five N rates (0, 50, 100, 150and 200kg/ha) as the sub plot treatments and five rice varieties (Cisadane, Suakoko 8, IR 5, ITA 306 and MAS 2401) as the main plot treatments. Nitrogen was band applied as urea in two equal splits at 2 and 8 weeks after transplanting (WAT). The results showed that the grain yield and growth parameters of the rice varieties were significantly (P<0.05) increased by the various N rates. In particular, the rate of 150kg/ha was consistently superior to other rates in increasing yields. It produced the broadest leaf area and the highest number of spikes, per panicle in 2012 and the highest number of tillers per plant and the heaviest grain yield in both years. Among the varieties, Suakoko 8 gave the highest significant (P< 0.05) yield response to the applied N fertilizer, followed by IR 5 and MAS 2401 (no significant difference) ITA 306 and Cisadane, in that order. Application of 150kg/ha of N in the form of urea to Suakoko 8 variety is recommended for the area.
KEYWORD: Nitrogen rates, rice varieties, response, growth and yield.