The Effect of Deficit Irrigation on Root/shoot Ratio, Water Use Efficiency and Yield Efficiency of Soybean

概要

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An experiment was conducted in a vinyl house at Gifu University, Japan, from June to November 2008 to investigate the effects of water stress on root/shoot ratio and water use efficiency (WUE) at different growth stages, and its influence on yield efficiency (YE) of soybean. The treatment imposed was deficit irrigation with five levels including D_1(0-20%), D_2(20-40%), D_3(40-60%), D_4(60-80%), and D_5(80-100%) water deficits of total available water. Soybean seed yield (Y) significantly correlated to the crop water requirement (CWR) as well as to the leaf area index (LAI) and total dry biomass (TDB) in response to water deficit levels. These relationships indicated the water stress decreased CWR which in turn caused the decrease in LAI and TDB and a subsequent decrease in grain yield. However, WUE and YE values increased with increasing root/shoot ratio up to the D_4 treatment and thereafter, decreased up to the D_5 treatment in response to increasing water deficit levels. The study showed that the most effective economic water usage with the highest YE was at D_4 water deficit. It could produce 21% lower yield per plant, but could conserve 18% irrigated water to produce the same yield compared to the potential yield produced under full irrigation (D_1).