Effects of Deficit Irrigation and Mulching on Seed Yield and Water Use of Onion (Allium cepa L.)

The effects of deficit irrigation and mulch on seed yield, water use and water productivity of onion was studied through a field experiment during 2012 - 2013 and 2013 - 2014 winter season at the experimental field of Bangladesh Agricultural Research Institute, Gazipur, Bangladesh. Eight treatments comprising of four levels of irrigation regimes (40, 60, 80, and 100% soil moisture deficit (SMD)) and two levels of mulching (no-mulch and rice straw) were tried in randomized complete block design with three replications. Both irrigation and mulch exerted significant effects on the yield and yield contributing parameters of onion. On average, the seed yield ranged from 1061 to 1595 kg ha-1, with minimum in treatment of 40% DSM without mulch and maximum in full irrigated (100% DSM) mulch treatment, respectively. The seed yields of the treatments irrigated up to 80% DSM were not statistically (p= .05) different from those that were fully irrigated (100% DSM). Analyses of results showed that irrigating onion up to 40% DSM reduced seed yield by about 30%. Applying water up to 60% of DSM caused a yield reduction of about 19%. However, irrigating onion up to 80% of DSM reduced seed yield by less than 4%. Results also revealed that water use of onion crop were largely influenced by the depths of water applied rather than mulching. On average, total water use ranged from 177 to 262 mm with minimum in mulch treatment of 40% DSM and maximum in full irrigated treatment. Total water used by the mulch treatments was only 5.08% lower than that of the non-mulched treatments. While difference in total water applied between mulched and non-mulched treatments was 7.2%. Water productivity was found to be the highest (0.71 kg m-3) in the mulched treatment (80% DSM) with total water use of 220 mm. This treatment also produced near to the highest yield with 22% saving of irrigation water meaning that irrigating up to 80% DSM with mulch may be the best practice for seed production of onion.