灌漑・排水システム工学

Irrigation is the only solution to improve crop production and productivity thereby contributing towards food security, self-sufficiency and export market. The efficient use of water by irrigation system is becoming increasingly important in arid and semi-arid regions with limited water resources. The Experiment was conducted in Debre Zeit Agricultural Research Center with the Regulated Deficit Irrigation and Onion (Allium cepa L.) Yield Response on Water Productivity in Ethiopia during 2017/2018 cropping season. The objective of the experiment was identify the pin point of water stress threshold value of onion under deficit irrigation and investigate the effect of alternate, fixed and conventional furrow irrigation methods on crop yield and water productivity under deficit irrigation. The experimental treatments had three furrow irrigation methods, (alternate furrow irrigation (AFI), fixed furrow irrigation (FFI) and conventional furrow irrigation (CFI)) and two deficit irrigation levels of application, viz., 85 % ETc, and70 % ETc and a control irrigation of 100%ETc. The design of the experimental plot was split plot in RCBD arrangement and replicated three times. The three furrow irrigation methods were arranged as main plots and the deficit levels as sub plots a total of nine (9) treatment combinations. All collected data, were statistically analyzed using SAS 9.1 statistical software. The experimental study result showed that bulb diameter, unmarketable bulb yield and total bulb yield of onion were highly significance difference (p<0.001) both in furrow irrigation methods and irrigation levels. Likewise diameter of onion also gave highest on CFI and 100%ETc irrigation water application level which is 6.69cm and 6.94cm respectively. According to the results obtained, the highest total yield was recorded for the treatment of 100%ETc irrigation water application and AFI of the furrow irrigation method 38947kgha-1 and 35920kgha-1 respectively however, the lowest total bulb yield of 30253kg ha-1 and 29135kg ha-1 were recorded when FFI system was applied and in 70%ETc of water applied. Bulb height of onion was highly significance difference (p<0.001) only on deficit irrigation levels. On the other hand, marketable bulb yield, irrigation water use efficiency and crop water use efficiency were significance difference (P ≤ 0.05) by the interaction of furrow irrigation methods and deficit irrigation levels. The highest average marketable bulb yield of onion was obtained 42219kgha-1 on CFI with the combination of 100%ETc irrigation level in addition to this IWUE and CWUE both are recorded highest result on 70%ETc and AFI furrow irrigation method. Generally, among all irrigation treatments 70%ETc deficit irrigation level applied under AFI method was efficient in conserving significant irrigation water. Therefore, it could be concluded that, AFI can save a substantial amount of water and labor without highly reduction of onion yield and the lowest CWUE and IWUE was gave FFI followed by CFI.

The study was conducted at Wondo Genet Agricultural Research Center, SNNP Region, Ethiopia, 7°05’ N latitude, 38°37’ E longitude and 1785 m.a.s.l for two years (2013/14 to 2014/15) based on the objective to evaluate the response of lemongrass (Cymbopogoncitratus (DC) Stapf) to supplementary irrigation (SI) at different levels and different growth stages. Five levels of SI (100, 75, 50, 25% and no SI) and three supplementary irrigation at growth stages (one SI at mid-season, one SI at maturity and two SI at mid-season and maturity stages) with three replications were used in randomized complete block design. Application of supplementary irrigation to lemongrass had a highly significant (p<0.01) effect on fresh biomass, essential oil content and water use efficiency during the first year. Significant (p<0.05) effect was also observed in dry biomass and essential oil yield. However, no significant (p>0.05) effect was observed on number of tiller per hill. Highly significant (p<0.01) influence was observed on fresh biomass, dry biomass and water use efficiency during the second year. Though essential oil content affected significantly (p<0.05), no significant (p>0.05) variation was observed in essential oil yield due to supplementary irrigation during the second year. Maximum (43.4 and 60.1 t/ha) and minimum (29.7 and 51.1 t/ha) annual fresh biomass production were recorded at 100% ETC SI and rain-fed treatment both years, respectively. Similarly, maximum (9.15 and 13.8 t/ha) and minimum (5.74 and 11.4 t/ha) annual dry biomass production were recorded at 100% ETC SI and rain-fed treatments both years, respectively. Maximum (0.55 and 0.64%) essential oil content was observed at application of two SI at mid-season and late season stage and rainfed treatment during the first and the second year, respectively. Conversely, minimum (0.44 and 0.55%) essential oil content was observed at 100% ETC SI both years. Maximum annual essential oil production of 219.8 and 219.7 kg/ha were recorded at 75% ETC and two SI at mid-season and maturity stage during the first year. Minimum annual essential oil production of 152.2 kg/ha was recorded at rain-fed (no supplemental irrigation) treatment during the first year. The maximum (0.59 and 1.47 kg/mm) and minimum (0.19 and 0.28 kg/mm) water use efficiency was recorded at rain-fed treatment and 100% ETC SI during both years, respectively.