Determination of Optimal Irrigation Using Soil Moisture Depletion on Yield and Water Productivity of Onion at Odo Shakiso District, Southern Ethiopia

Abstract

Irrigation scheduling is the use of water management strategies to prevent over-application of water while minimizing yield losses due to water scarcity or drought stress. The experiment was conducted in Odo Shakiso district at a farm during the 2020/21 and 2021/22 irrigation seasons with the aim of determining the optimal irrigation schedule for yield, yield component and water productivity of onions based on the available soil moisture depletion levels. The experiment was performed in RCBD with three replicates randomly assigned to experimental plots with treatments. Five available soil moisture depletion levels (20% ASMDL, 40% ASMDL, 60% ASMDL, 80% ASMDL and FAO recommended ASMDL) were used for treatment. Results from two years of research showed that different levels of available soil moisture had a significant impact (P<0.05) on bulb diameter, bulb weight, unmarketable onion yield, marketable onion yield, and water productivity. However, different soil moisture depletion did not show a significant difference in plant height. The highest onion diameter (4.25 cm) and marketable onion yield (363.9 qt/ha) was recorded at 60% ASMDL. The highest water use efficiency at marketable onion yield (9.487 kg/m³) was also achieved at 60% ASMDL, which was statistically comparable to the FAO-recommended ASMDL treatment. On the other hand, the minimum water use efficiency (6.234 kg/m³) was recorded at 40 percent ASMDL. Therefore, based on the results of the current experiment, it is recommended to use 60% ASMDL under a furrow irrigation system for onion cultivation in areas around Shakiso and similar agro ecologies as it is the best option to increase yield and water use efficiency for onion production.