Effects of regulated deficit irrigation and mulch on yield, water use and crop water productivity of onion in Samaru, Nigeria

This paper presents the findings of the effects of regulated deficit irrigation and mulch materials on yield, water use and water productivity of onion crop. The field experiments were conducted in 2008/09 and 2009/10 irrigation seasons at the Institute for Agricultural Research Samaru Zaria, Nigeria. Sixteen treatments comprising of four levels of water application depths (irrigating at 25, 50, 75, and 100% weekly reference evapotranspiration (WRET)) and four levels of mulching (no-mulch, using rice straws, black and white transparent polyethylene materials) were studied each season. Surface irrigation was used and the crop was planted in basins. Water applied per irrigation, soil moisture contents before and after irrigation was monitored throughout the seasons while the harvested bulb yields were weighted and graded. The bulb yields in the two seasons ranged from 6.3 to 20.6 t/ha. The seasonal water applied varied from 225 to 480 mm while the seasonal evapotranspiration (SET) computed from the soil moisture contents ranged from 201 to 376.3 mm. Further analyses of results showed that irrigating onion at 25% of WRET reduced bulb yield by about 50%. Applying water at 50% of WRET caused a yield reduction of about 15.5–23.0%. However, irrigating onion at 75% of WRET reduced bulb yield by less than 10%. Results also revealed that seasonal evapotranspiration (SET) of the onion crop were largely influenced by the depths of water applied rather than mulching. Irrigating the onion crop at 50 and 75% of WRET gives higher water productivity in terms of water supplied for the onion crop. Mulching with rice straw or black polyethylene did significantly improve the crop water productivity of the onion crop. In order to maximize irrigation water utilization under limited water supply to improve crop water productivity in the study area, onion crop should be mulched with rice or black polyethylene and water application depth per irrigation should be kept at 50–75% weekly reference evapotranspiration.

► Bulb yield of onion was highly influenced by regulated deficit irrigation and mulch covers.
► Seasonal water use of the onion crop was influenced by deficit irrigation but mulching did not affect seasonal water use.
► The crop water productivity of the onion crop was however influenced by both deficit irrigation and mulch cover.