| Summary: | Despite its very recent history of cultivation in Ethiopia, rice is one of the potential grain crops that could contribute to the efforts for the realization of food security in the country. However, the scientific information available with regards to the response of flooded rice to N and P fertilizers for its optimum production on Vertisols of Fogera Plain is very limited. Therefore, a field experiment was conducted on Vertisols of Fogera plain, northern Ethiopia to study the yield and yield components response of rice and to establish the optimum N and P fertilizer levels required for improved grain yield of flooded rice. Six levels of N (0, 30, 60, 90, 120 and 150 kg ha−1) and five levels of P (0, 13.2, 26.4, 39.6 and 52.8 kg ha−1) laid down in a randomized complete block design with four replications were used as treatments. Nitrogen was applied in two equal splits (50% basal and 50% at maximum tillering) as urea and the entire dose of P was applied basal as triple super phosphate at sowing. The main effects of N and P fertilizer levels showed significant differences (P ≤ 0.01) for all yield and yield components studied. The effects of N by P interaction were significant only for grain yield (P ≤ 0.05), number of panicles per m2 (P ≤ 0.01), number of spikelets per panicle (P ≤ 0.05) and plant height (P ≤ 0.01) among the different yield and yield components studied. Application of N and P significantly (P ≤ 0.01) increased grain yield of rice up to the levels of 60 kg N and 13.2 kg P ha−1. However, maximum grain yield (4282 kg ha−1) was obtained with the combined application of 60 kg N and 13.2 kg P ha−1, and the yield advantage over the control was 38.49% (1190 kg ha−1). Moreover, application of both N and P fertilizers have increased the magnitudes of the important yield attributes including number of panicles per m2, number of spikelets per panicle, panicle length, dry matter accumulation, straw yield and plant height significantly (P ≤ 0.01). Besides, grain yield was positively and significantly associated with number of panicles per m2 (r = 0.61∗∗), number of spikelets per panicle (r = 0.49∗∗), panicle length (r = 0.54∗∗), dry matter accumulation (r = 0.46∗), thousand grain weight (r = 0.41∗) and harvest index (r = 0.39∗). These indicate that N and P application increased grain yield of rice by positively affecting the important yield components of the crop. Therefore, taking the findings of the present study into consideration, it may be tentatively concluded that the farmers at the Fogera plain may apply a combination of 60 kg N and 13.2 kg P ha−1 to improve the grain yield of flooded lowland rice cultivated on heavy black clay soils (Vertisols) under rain fed conditions.
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