Abstract:
Potato is an important food and cash crop in eastern Ethiopia including Oda Bultum District of West Hararghe Zone. However, there is no information on the role of blended NPSB fertilizer required to produce tuber yield and tuber quality traits of potato varieties in Oda Bultum District. A field experiment was conducted in Oda Bultum District, under rainfed during 2018 cropping season, with the objectives of assessing the effects of blended NPSB fertilizer rates on yield-related traits and tuber yield of potato varieties and to estimate the cost-benefit of the application of blended NPSB fertilizer in potato production. The treatments consisted of two potato varieties (Bubu and Gudanie) and six rates of blended NPSB (0, 100, 150, 200, 250 and 300 kg NPSB ha-1) fertilizer. The experiment was laid out as a Randomized Complete Block Design in a 6 x 2 factorial arrangement and replicated three times. Analysis of variance revealed that the two main factors; blended NPSB and variety had a significant effect on all traits except that fertilizer and variety had a non-significant effect on days to 50% emergence, unmarketable tuber number per hill and large tuber size, respectively. Interaction of blended NPSB fertilizer and variety had a significant effect on total tuber number/hill, average tuber weight, total and marketable tuber yields (t ha-1). Gudanie variety emerged, flowered and matured earlier than Bubu. Early flowering of the crop was observed in a plot which did not receive fertilizer while the application of NPSB fertilizer delayed flowering and maturity of plants that received highest rates NPSB fertilizer (200, 250 and 300 kg ha-1). Bubu variety had significantly tallest plant height (62.44 cm) than Gudanie when received highest rates of NPSB fertilizer (300 and 250 kg ha-1). Bubu had the highest number of main stem/hill (8.33) and average tuber weight (72.33g) at the rate of 300 kg ha-1 NPSB fertilizer while the highest total tuber number hill-1(16.00) was obtained from Gudanie variety at the application of 200 kg ha-1NPSB fertilizer. The highest proportion of small size tubers were obtained from plots than received no fertilizer while the largest proportion of large size tubers were obtained from plots that received 200, 250 and 300 kg ha-1 NPSB fertilizer. Bubu produced significantly higher fresh and total dry biomass than Gudanie. Application of 150 to 300 kg ha-1 fertilizer gave higher fresh and dry biomass than the application of 0 and 100 kg ha-1 NPSB fertilizer. The highest total and marketable tuber yields of 30.55 and 27.22 t ha-1, respectively, were obtained from Gudanie variety with the application of 200 kg ha-1 NPSB fertilizer. Gudanie had a significantly higher specific gravity (1.085g/cm3), tuber dry matter (21.98%) and starch content (15.82%) while plants produced tubers with highest specific gravity, tuber dry matter and starch content due to the application of 200 kg ha-1 NPSB fertilizer. Moreover, the highest net benefit of 116,330.24 Birr ha-1 with 4066% marginal rate of return were obtained from growing of Gudanie variety with the application of 200 kg ha-1NPSB plus 100 kg ha-1 urea fertilizer that could be recommended for production of potato in the study area. Further study should be done over more seasons and locations to establish the scientific recommendations so as to improve the production and productivity of potato in the study area.