To avoid over or under irrigation, it is important to know how much water is available to the plant, and how efficiently the crop
can use it which mean irrigation scheduling. The study was conducted to evaluate the response of Onion to irrigation regime and
determination of water use efficiency. The experiment had five treatments which were soil moisture depletion levels, 60% of
available soil moisture depletion level, 80% of available soil moisture depletion level, 100% of available soil moisture depletion
level, 120% of available soil moisture depletion level and 140% of available soil moisture depletion level and arranged in
randomized complete block design. The experiment was tested on Bombay Red onion variety. Soil parameters like bulk density,
texture, field capacity and permanent wilting point were analyzed. Climatic data like minimum and maximum temperature and
rainfall, wind speed at two meter height, relative humidity and sunshine hours were collected which were inputs to determine
reference evapotranspiration. The water requirement of was calculated by taking into consideration the growth periods (initial,
development, mid-season and late season) and soil moisture depletion levels. The highest onion bulb yield and water use
efficiency were obtained from 60% of available soil moisture depletion level. Irrigation interval of 6 days was required but it is
recommended to use irrigation interval depending on growth stages which give an optimum Onion bulb yield and water use
efficiency.
Keywords: Assosa, Irrigation scheduling, Onion, Water requirement
