EFFECTS OF DEFICIT IRRIGATION AND MULCH LEVELS ON GROWTH, YIELD AND WATER PRODUCTIVITY OF ONION (Allium cepa L.) AT WERER, MIDDLE AWASH VALLEY, ETHIOPIA

Abstract

Enhancing water productivity of irrigated crops through water management is a vital option in water scarce areas, such as, Rift valley. Accordingly a field experiment was conducted at Werer Agricultural Research center to evaluate the effects of deficit irrigation and straw mulching levels on growth, yield and water productivity of onion (Allium cepa L.). The experiment was laid out in a randomized complete block design in factorial arrangement of three levels of irrigation (100, 80 and 60% of ETc) and four levels of straw mulch (0, 3, 6 and 9ton wheat straw per ha) in three replications. The output of Cropwat model indicated that the highest seasonal water requirement of onion was 422.5 mm at 100% ETc while; the lowest was 253.5 mm at 60% ETc. The analysis of variance revealed that statistically, there was significant (p<0.05) difference in days to maturity, plant height and leaf length; and Number of leaves per plant, leaf diameter, neck diameter, bulb length, bulb diameter, average bulb weight, marketable bulb yield and total bulb yield were highly significant (p<0.01) influenced by the interaction effects of deficit irrigation and straw mulch levels. The highest marketable bulb yield (33.47 t/ha) was obtained from an experimental plot treated with combined application of 100% of ETc and 6 t/ha straw mulch, while the lowest (21.10 t/ha) was obtained from plots treated with 60% ETc irrigation level and no mulch treatment. Water productivity was also highly significant (p<0.01) influenced by the interaction effects of deficit irrigation and straw mulching levels; the highest (10.22 kg/m3) and the lowest (6.11 kg/m3) were recorded from the plots treated with 60% ETc and 9 t/ha straw mulch, and 100% ETc and no mulch treatments, respectively. Partial budget analysis revealed that the most economically attractive combination for small scale farmers with lower cost of production and higher net benefits was from the application of 80% ETc and 6 t/ha straw mulch. Therefore, in terms of marketable bulb yield and water profitable productivity, irrigating with 80% ETc with 6 t/ha straw mulch would be recommended for production of onion in the study area.