Abstract:
Scarcity of water is the most severe constraint for development of agriculture in arid and
semi-arid areas. Under such conditions, the need to use the available water economically and
efficiently is indisputable. The important strategy for increasing water productivity and
improving water use efficiency in the area of water scarcity, was deficit irrigation. A field
experiment was conducted at Mehoni Agricultural Research Center during off season aimed at
investigating the effect of deficit irrigation levels on water productivity of onion (Bombey Red
variety) and the most sensitive growth stages of onion crop. The experiment was carried out in
split plot design with sixteen treatment combinations and three replications. Treatments
include four growth stages (initial, development, bulb formation and maturation) as main plot,
and three deficit irrigation levels (80%, 60% and 40% of ETc), and one control irrigation of
100% ETc as subplot. Crop water requirement was estimated using actual daily climatic data.
The result showed that deficit irrigation levels, time of deficit irrigation and their interaction
had significant (p< 0.01) effect on bulb yield and yield components. The treatments receiving
100% ETc at the time of development stage gave the highest total bulb yield of 30.67 t/ha with
no significant difference from 60% deficit treatments during initial and maturation stages.
The result showed that initial and maturation stages were the right time to practicing deficit
irrigation without significant yield reduction. Water productivity was the highest with 60%
deficit irrigation at maturation stage (8.96 kg/m3), and 0.17ha additional area to be irrigated
by saved water. The yield response factor (Ky) was higher (1.98) when 40% deficit occurred at
development stage. The result revealed that onion bulb yield was most sensitive to water
deficit that occurred at development and bulb formation stages. While maximum yield was
obtained when the whole crop water requirement was fulfilled, practicing deficit irrigation at
appropriate stage could increase the irrigated area as a result of high water use productivity
