Irrigation & Drainage Systems Engineering

Irrigation is a vital practice in the Central Rift Valley of Ethiopia. However, water scarcity is the major limiting factor to agricultural production and productivity in the area. A field experiment was conducted on clay loam soil at the experimental field of Melkassa Agricultural Research Centre with the objectives of determining optimal Nitrogen fertilizer rate and soil moisture level for the onion yield and water productivity. The experiment was arranged in split-plot design with three replications. The treatments include three soil moisture levels (100% ETc, 75% ETc and 50% ETc) as main plot and four nitrogen fertilizer rates of 23, 46, 69, 92 and no nitrogen as a sub-plot. The highest average bulb yield of 28.6 t/ha was obtained at the full application of irrigation(100% ETc) and the lowest average bulb yield of 22.8 t/ha was recorded at 50% level of irrigation deficit. Onion bulb yield increased significantly with an increase in nitrogen fertilization from 23 to 92 N rate kg/ha. The highest average bulb yield of 30.1 t/ha was obtained at the 92 Kg/ha N rate and the lowest average bulb yield of 20.1 t/ha was recorded from no application of nitrogen rate. The highest bulb yield of 33.1 t/ha was recorded from the fully irrigated that combined with high nitrogen levels. Moisture stress at different deficit levels with the nitrogen levels had a significant (p<0.05) influence on water productivity. Water productivity was higher for 92 N-rate kg/ha treatment and minimum water productivity was obtained at zero nitrogen rate treatment. Therefore, under a limited water area, it can be concluded that more water-saving and an associated increase in water productivity with high nitrogen fertilizer resulting in a yield increment of the onion by 32.5% can solve the problem of water shortage.

Irrigation scheduling is the use of water management strategies to prevent over application of water while minimizing yield loss due to water shortage or drought stress. The experiment was performed at Odo shakiso District on farm in the 2020/21 and 2021/22 irrigation seasons, with the objective of determining the optimum irrigation schedule on Yield, yield component and water productivity of Onion based on the available soil moisture depletion levels. The experiment was carried out in RCBD with three replications, randomly assigned to the experimental plots with treatments. Five available soil moisture depletion levels (20% ASMDL, 40% ASMDL, 60% ASMDL, 80% ASMDL and FAO recommended ASMDL) were used as treatment. The results obtained of two years of research showed that different of levels of soil moisture available had a significant effect (P< 0.05) on bulb diameter, bulb weight, unmarketable bulb yield, marketable bulb yield, and water productivity. However, different soil moisture depletion levels showed no significant difference on plant height. The highest bulb diameter (4.25 cm) and marketable bulb yield (363.9 qt/ha) were recorded at 60%ASMDL. The highest efficiency of water use on marketable onion yield (9.487 kg/m³) was also attained at 60%ASMDL, which was statistically similar with FAO recommended ASMDL treatment. On the other hand the minimum efficiency of water use (6.234 kg/m³) was recorded at 40 per cent ASMDL. Therefore, based on the findings of the current experiment, it is recommended that using 60%ASMDL under furrow irrigation system for onion to be grown in areas around Shakiso and similar agro-ecology as best options to increase yield and water use efficiency for the production of onion.