Irrigation water management for efficient water use in mulched onion

Abstract

The effects of mulch and five levels of irrigation on soil evaporation, transpiration evapotranspiration, and yield of onion were studied in a glasshouse pot experiment during 1996-1997 (December 1, 1996 to May 14, 1997). Five different levels of irrigation were imposed on covered and open clay loam soil surfaces in four replicates. Water losses by evaporation and, or transpiration were measured daily by weighing. Irrigation water was applied once weekly. The amount of irrigation water added to each treatment was determined from weight differences. Increasing applied irrigation water significantly increased evapotranspiration and or transpiration. With mulch treatments, evapotranspiration was significantly reduced, while transpiration was significantly increased compared with open soil surface treatments. Covering the soil surface reduced the amount of irrigation required water by the onion crop by about 70 % for all irrigation treatments compared with the amount of irrigation water added in the open soil surface treatments, because wet soil surface evaporation was eliminated. Increasing the amount of water applied increased the evaporation transpiration ratio as a result of an increase in water available for evaporation. In the onion crop, most off the irrigation water (about 1.7 times transpiration) was lost in evaporation. For both covered and open soil surface treatments, the actual measured potential transpiration depth was about 150 mm compared to about 400 mm evapotranspiration depth in the open soil surface treatment. In covered soil surface treatments, onion yields were significantly higher than in open surface treatments at low water levels because of the significant soil evaporation associated with open soil surface treatments. However, onion yields for open and covered soil surfaces became comparable as the total water applied increased. Water use efficiency., in the covered soil surface treatment was maximum for the highest water level (W4 = 197 mm irrigation), while in the open soil surface treatment, water use efficiency was maximum for the intermediate water level (W2 - 209 mm irrigation).