Potato is the secondary non-cereal crop in Ethiopia, of which around 1,288,146 household farmers depend on it. Potato harvesting is practiced using animal-drawn local plough (Maresha) and hand hoe, which is characterized by high man-hour requirement, drudgery, and considerable losses through tuber damage and inefficient exposure. Thus, a single axle tractor-operated potato digger elevator was designed, fabricated and evaluated to be used by Ethiopian smallholder farmers. The major parts of the potato digger were a soil-cutting blade, shanks, chain and rod conveyor, depth control wheels, power transmission system, and eccentric discs. The soil of the field was a clay loam soil texture with 32% sand, 42% silt, 26% clay. Field experiment was conducted to evaluate conveyor slope and rake angle of the potato digger. The field experimental design used was laid in a split-plot design where the conveyor slope (10°, 15°, and 20°) was the main plot; the rake angle (15°, 20°, and 25°) was sub-plots design with 32 factorial experiments and 3 replicates as block giving 27 total experimental units. Tubers of Belete potato variety widely grown in the country were used for performance evaluation. The prototype machine was evaluated to see these effects in terms of different parameters. The experimental result revealed that tuber damage loss decreased when increasing the rake angle but increased with conveyor slope. The maximum exposure efficiency of 96.47% was obtained when the machine was operated at a conveyor slope of 15° and the rake angle of 20°. Increasing the rake angle and conveyor slope up to 20° and 15° respectively, resulting in increased exposure efficiency, and it declined gradually at 25° and 20° rake angle and conveyor slope, respectively. At this optimum condition, damage percentage, conveyance efficiency, cleaning efficiency, drawbar pull, fuel consumption, wheel slip, soil swelling factor, soil mean weight diameter, pulverization ratio, and field capacity were 3.39%, 89.64%, 91.87%, 2959.1N, 14.87 Litre/ha, 17.67%, 20.25%, 17.44 mm, 78.09% and 0.127 ha/h respectively. From performance indicators, it can be concluded that the machine is acceptable with a high prospect for adoption for small and medium-scale farmers. The prototype must be re-evaluated at a more rake angle and conveyor slope using different potato varieties; with additional levels and double axel tractor.
Keywords: Design, Construction, Evaluation, Conveyor Slope, Rake Angle, Potato Tuber, Digger