Response of Some Improved Upland Rice Varieties to Different Sources and Rates of Nitrogen Fertilizer in A Humid Rain Forest Region

Nitrogen (N) is a major lacking nutrient element for the growth and yield of cereal crops Calabar, it is necessary to determine the response different sources and rates of N in four varieties of upland rice. Treatments comprised factorial combinations of the four rice varieties (NERICA 1, NERICA 2, FARO 45, FARO 48), three straight inorganic N sources (urea, Calcium ammonium nitrate, ammonium sulphate) and four levels of N (0, 30, 60, 90 kg N ha-1) laid in randomized complete block design. The N was split applied twice; one-third at the beginning of tillering and the remainder at panicle initiation. The results showed that the source of fertilizer N did not affect significantly the growth and yield of the rice crop (p=0.05). Considering that soils in Calabar are acid sands it will not be advisable to consistently apply such acidifying fertilizers as ammonium sulphate or urea except with soil liming which will undoubtedly increase the cost of production and probably make it unprofitable to cultivate rice in the area. The fertilized crop grew taller and produced more biomass compared with the control. It also produced significantly more tillers hill-1, panicles m-2, grains panicle-1, weight of 1,000 grains and grain yield. However, whereas NERICA 1, NERICA 2 and FARO 45 were more responsive to lower N levels, the grain yield of FARO 48 was significantly higher when the crop received 90 kg N ha-1 compared with other varieties, probably because of its longer growth duration in the field. The responsiveness of these varieties to low N application was the result of their higher grain yield resulting from enhanced N use efficiency. Genotypes that were most responsive to low N input levels were early maturing with high N-use efficiencies. On the basis of grain yield, it is recommended that for high yield in the humid region of Cross River State, N should be applied at the rate of 60 kg ha-1 for early- and 90 kg ha-1 or above for the medium-maturing upland rice varieties