Deficit irrigation practices as alternative means of improving water use efficiencies in irrigated agriculture: Case study of maize crop at Arba Minch, Ethiopia

Deficit irrigation is becoming an important strategy to reduce agricultural water use in arid and semiarid regions. A field experiment was conducted in 2007 to examine the effect of deficit irrigation on the yield performance of maize crop under Arba Minch (Ethiopia) condition. Based on four phonological growth stages (establishment, vegetative, flowering and grain-filling stages) of maize, the crop was subjected to water deficit during one, two or three growth stages. The highest yield obtained was 5.933 tons/ha and the lowest was 3.467 tons/ha. Treatments that were water stressed during single growth stages such as first and second as well as consecutively during two stages, that is, first and second growth stages produced yields that are not significantly different from the yield achieved under fully irrigated treatment. Compared to the maximum yield, 29 to 42% lower yields were registered under treatments that were subjected to water deficit during three growth stages. Not only frequency of water deficit periods but also its timing was found to have effect on the final yield. Treatments which were stressed during two growth stages had 2.2 (0011) to 38.5% (1010) yield reduction compared to the maximum yield. The highest yield reduction was observed under the treatment which was irrigated only during the fourth growth stage (0001), followed by treatment irrigated during first and third growth stages (1010) and then treatments irrigated only during second stage (0100). This shows that prolonged deficit over three growing stages will have more yield reduction impacts. Plots stressed during third and fourth growth stages were found to produce lower yields indicating the severe effects of water stress during flowering (tasseling and silking) and early grain-filling stages on yield. The comparison of water savings achieved under different treatments that had no significant differences in yield level from full irrigated plot (1111I) ranged from 18.2% (treatments 0111 and 1011) to 36.4% (0011). This indicates that water deficit during first and second growth stages had no significant effect on the grain yield of corn and it is worthwhile to save irrigation water under this condition. The water use efficiency increased with decreasing water supply and increasing yield level. Irrigation water use efficiency increased with decreasing water supply and related yield which may not be desirable from farmers' perspective.