A study was conducted on a research station at Kobo sub-center of Sirinka Agricultural research Center for two years to determine the optimum rates of N and P fertilizers for green maize production under irrigation in Kobo-Girana irrigation valley. Four levels of N (0, 46, 92 and 138 kg N ha -1 ) with three levels of P fertilizer (0, 23 and 46 kg P2O5 ha -1 ) were factorially combined and laid in RCBD design with three replications. A uniform irrigation water depth and interval was applied to

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... l plots based on maize's irrigation water requirement determined for the area. The crop was irrigated a total amount of 500 mm irrigation water at 7 days interval starting from the development stage. Phosphorus fertilizer was applied all at planting. While, N fertilizer was applied in split, 1/3 at planting, 1/3 at knee height and 1/3 at tasseling stage. The result shows that there was no significant (p>0.05) interaction of N and P fertilizers on the cob yield, cob number, cob length and cob diameter of green maize. However, the main effect of N fertilizer had significant (p<0.05) effect on the cob yield, cob number, cob length and cob diameter of green maize. The main effect of application of P fertilizer had insignificant (p>0.05) effect on the cob yield of green maize, which is attributable to the medium to high levels of Olsen's extractable available P in bottom valleys of alluvial soils of Kobo where the study site laid. The highest cob number (51556) and cob weight (12.0 t ha -1 ) was recorded from application of 138 kg N ha -1 followed with statistically insignificant (p>0.05) difference by the cob number (49020) and cob weight (11.1 t ha -1 ) obtained from application of 92 kg N ha -1 . The partial budget and the sensitivity analysis result considering 15% possible price fluctuation show that the highest marginal rate return of 421.7% was obtained from application of 92 kg N ha -1 . While, the lowest marginal rate return of 378.8% was recorded from application 138 kg N ha -1 . Therefore, application of 92 kg N ha -1 is recommended for maximum and economic return of green maize production under irrigation in Kobo valley.