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A field experiment was conducted to determine the effects of different rates of NPK fertilizer on performance of Irish potato (Solanum tuberosum L.). This experiment employed use of 150 and 300 kg ha^-1 of NPK (23:10:5) fertilizer and a local cultivar Alika of Irish potato as a response crop. Results indicated that the significantly (p < 0.05) highest average marketable number of tubers per plant (3.5) and tuber yield (18.74 t ha^-1) was recorded at an application of 300 kg NPK ha^-1. The lowest average number of tubers per plant (2.2) was recorded in the absolute control while the lowest tuber yield (14.99 t ha^-1) was recorded at 150 kg NPK ha^-1 compared with the absolute control (15.97 t ha^-1). The coefficients of determination (R2) from the linear regression model showed that the variation in tuber yield was 50.7% with NPK fertilizer, 21.4% with number of tubers per plant and 23.6% with tubers per plot. Partial budget analysis indicated that the net benefit was in the decreasing order of 300 kg NPK ha^-1 (5,335,500 Tshs/ha) > absolute control (4,135,000 Tshs/ha) >150 kg NPK ha^-1 (3,552,000 Tshs/ha). The benefit cost ratios obtained for the absolute control, 150 and 300 kg NPK ha^-1 were 2.1, 1.9 and 2.3, respectively, while the marginal rate of return for the two rates of fertilizer were -0.45 and 1.27, respectively. Based on the total variable costs and net benefit, NPK applied at 150 kg ha^-1 was dominated (D) by the absolute control.

Key words: Partial budget, Irish potato cv. Alika, tuber yield.

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Citation: Shaaban H, Kisetu E (2014). Response of Irish potato to NPK fertilizer application and its economic return when grown on an Ultisol of Morogoro, Tanzania. J. Agric. Crop Res. 2(9): 188-196.