Genotype and Seeding Date Effects on Performance of Mangrove Rice (Oryza sativa L.) In the Cross River Estuary

The mangrove swamp soils of the Cross River estuary are suitable for intensive rice cultivation because of ample water supply, large level units and high inherent fertility. However, because water is abundant, rainfall does not determine the sowing period. Field studies were conducted in 2006 and 2007 at Obufa Esuk Orok adjacent the University of Calabar Teaching and Research Farm to determine the best seeding date for two salt-tolerant rice varieties grown on a mangrove swamp soil in the Cross River estuary, southeastern Nigeria. Two mangrove rice varieties namely ROC 5 and CK 73 were raised in nurseries on 6 December, 8 January, 4 February and 4 March, of each year and 30 day-old seedlings transplanted at a plant spacing of 20x20 cm and at 2 seedlings per hill. Treatments comprised factorial combinations of four seeding dates and two varieties laid out in a split-plot design; the main- plot being the date of seeding and the sub-plot the variety. Significant varietal differences were observed, with CK 73 performing better than ROC 5. During the 2006 and 2007 growing seasons, paddy yield of 4.35 and 5.14 t ha-1 obtained from sowing in February was higher than yield values for December, January and March plantings by 14.5, 27.6 and 18.2% (2006) and 37.9, 41.8 and 18.9% (2007). Seeding conditions in December through January were unfavorable because in the absence of water control, the frequent and unpredictable tidal water flow washed away seeds and seedlings, leading to poor germination, seedling establishment and reduction of the crop’s tillering capacity and panicle formation. These conditions were ameliorated in February and March and the favorable solar radiation levels and temperature regime that subsisted in April and May when the February sown crop matured accounted for the superiority of this seeding period. It would however, be unsuitable to seed late-maturing varieties at this period because they would mature during the peak rains when natural drying conditions would be unfavorable.