1) The document summarizes a field experiment studying the effects of deficit irrigation and different mulch covers on water use and yield of drip-irrigated onions. 2) It found that onion bulb yield decreased with higher levels of water deficit, but water use efficiency increased. 3) Using straw mulch resulted in the highest onion yields, though it was similar to using clear or black plastic mulches. Straw mulch also provided significant water savings.

1. EFFECTS OF DEFICIT IRRIGATION AND MULCH ON WATER USE AND YIELD OF DRIP IRRIGATED ONION<br />By<br />NEGA, HUNE<br />(M.Sc/ENG/07295/2006-07)<br />A thesis submitted to the Post-Graduate School, Ahmadu Bello University, Zaria, Nigeria, in partial fulfillment of the requirements for the award of M.Sc. Degree in Agricultural Engineering.<br />Department of Agricultural Engineering <br />Faculty of Engineering<br />Ahmadu Bello University, Zaria<br />Nigeria<br />JULY, 2009<br />ABSTRACT<br />A field experiment was conducted at Melkassa Agricultural Research Center in the Central Rift valley of Ethiopia during the 2008/2009 dry season to study the “Effect of deficit Irrigation and different mulch covers on water use and yield of drip irrigated Onion“ (Allium Cepa L., cultivar: Bombay Red). A drip irrigation system with 144 laterals each 5 m long and 12 mm diameter with inline emitters was used in the experiment. Two factors, namely deficit irrigation at four levels (0, 25, 50 and 75 percent of Total Available Water, TAW) and mulch covers of four different types (no mulch or bare soil, straw mulch, clear plastic and black plastic) were combined in a randomized complete block design and laid out as treatments in plots (1.8 m wide x 5 m long). Three replications were used. The results showed that bulb yield decreased with increase in the level of water deficit, however, water use efficiency in terms of crop water use and irrigation water use efficiencies were increased with increase in the level of water deficit. Use of straw mulch resulted in a yield of 31.7 t/ha, though significantly higher than no mulch, it was at par with clear and black plastic mulches (at 5% level of probability). Significant water savings were recorded with straw, clear and black mulches in that order. The benefit-cost ratio decreased with increase in the level of deficit irrigation; however, among the mulch materials, straw mulch gave better economic performance in terms of low production cost, high profit and high benefit-cost ratio. The required rainwater tank size to irrigate 500 m2 land with drip irrigation varied from 82 to 195 m3 capacities. The average drippers flow rate variation, coefficient of uniformity and overall irrigation application efficiency of the drip irrigation system were found to be 13.7%, 96% and 94.4%, respectively.<br />