Abstract
An experiment was conducted in a vinyl house at Gifu University, Japan, from June to November 2007 to evaluate the potentialities of the three soil types under various water deficit conditions to yield of soybean. The soil type was the first factor with three different soil types, comprising of clay loam, sandy clay loam, and sandy loam soils, classified as Inceptisol, Ultisol, and Andisol, respec-tively. Water deficit (D) was the second factor with four levels including D1 (0 – 25 %), D2 (25 – 50 %), D3 (50 – 75 %) and D4 (75 – 100 %) water deficits of total available water (TAW). The crop water requirement (CWR) of soybean in the three soil types significantly decreased with the increas-ing water deficit levels, and the highest was in Incepti-sol, followed by Ultisol and then Andisol under all wa-ter deficit levels. Grain yield of soybean per unit area in Inceptisol was the highest, followed by Ultisol and then Andisol under all water deficit levels. The values of yield efficiency (YE), indicating the grain yield per unit CWR, was strongly influenced by water deficit level, and the max-imum YE occurred at the water deficit level D3 (50 – 75 %) in all the three soil types. However, there were no signif-icant differences at 5 % level among the maximum values of YE in the three soil types. The lowest yield response factor (Ky), indicating the relative yield loss to relative wa-ter deficit, was seen in Inceptisol (Ky = 0.42), followed by Ultisol (Ky = 0.64) and then Andisol (Ky = 0.87) under the water stress lower than 50 – 75 % of TAW. These results indicate that deficit irrigation in Inceptisol contained the finest soil texture is the most effective for economic water usage among the three soil types under the water deficit lower than 50 – 75 % of TAW (D3).
