Abstract:
Deficit irrigation (DT) is very essential in water scarce areas. Efficiency of irrigation can be improved by
making the right decision regarding to irrigation scheduling and irrigation application techniques. This
experiment was conducted to determine the most sensitive growth stages of onion to water stress so as to
maximize water use efficiency and yield of onion. The study was carried out for two consecutive years
(2011 and 2012). Four growth stages (Initial (I), Development (D). Mid (M) and Late (L) stages) and
four water application depths (100% application depth, 25% deficit, 50%stress and75% deficit) were
studied in factorial experiment. Irrigation was applied tlirough calibrated siphons with an irrigation
interval of six days under furrow irrigation methods. All relevant data were collected and analyzed and
significant treatment means were separated using least significant difference at 5%. The result showed
that effect of treatments on bulb diameter and bulb weight, marketable yield and total yield was
significant. The highest marketable yield (20.96 th a 1) was obtained from 25% stress at initial stage
followed by (20.77 t ha'1) 50% stress at initial stage while the lowest marketable yield (13.94 t ha'1) was
obtained from 75% stress at all stages. Full application of 40mm irrigation depth especially at the late
stage had resulted in the highest unmarketable yield while stressing by 50% at the initial stage gave the
highest marketable yield with a seasonal irrigation requirement of 540mm in the growing season.
Therefore, it is recommendable to apply irrigation water at 50% stress-(20mm irrigation depth)-at initial,
development and mid stages and 40mm at late stages every six days for onion.
