Effects of irrigation scheduling methods and blended NPS fertilizer on tuber yield and water productivity of potato (Solanum tuberosum L.) in northwest Ethiopia

Irrigation water scheduling methods influence the growth, yield, and water productivity of crops including potatoes. Therefore, a study was conducted to evaluate the effects of irrigation frequency determination methods on tuber yield, irrigation water productivity and fertilizer use efficiency of potatoes at Koga irrigation scheme, in Northwest Ethiopia. The treatments were consisted of two irrigation frequency determination methods (wetting front detector and crop water requirement) and six NPS fertilizer rates (0, 90.8, 136.2, 181.6, 227.4 and 272.0 kg ha-1, which were factorial combined in a randomized complete block design with three replications. Growth and tuber yield data of potato were collected based on the standard procedure. Irrigation water productivity, partial factor productivity, and agronomic efficiency were calculated using their respective models. The collected data were analyzed using SAS version 9.4. The results revealed that the wetting front detector method recorded the highest tuber weight (79.5 g), tuber yield (41.9 t ha-1), and irrigation water productivity (9.1 kg potato m- 3 water) compared to crop water requirement method. NPS fertilizer at the rate of 272 kg ha-1 also produced the highest tuber weight (86.5), tuber yield (58.1 t ha-1) and irrigation water productivity (12.4 kg potato m- 3 water). Treatment combination of wetting front detector and 272 kg ha-1 NPS recorded the highest plant height (64.m cm) and stem number (10.4). Wetting front detector method recorded the highest partial factor productivity (275.2 kg potato per kg NPS) compared to crop water requirement. Wetting front detector combined with NPS rates generally recorded higher partial factor productivity compared to the respective NPS rates combined with crop water requirement. NPS fertilizer at 272 kg ha-1 combined with wetting front detector gave the highest net benefit (236,591.7 ETB ha-1) with acceptable marginal rate of return (248.9%), which is recommended for economical production of potato in the area.