Abstract
An experiment was conducted in a vinyl house at Gifu University, Japan, from June to November 2008 to assess the effect of water stress on nodulation of uninoc-ulated soybean and leaf N accumulation to grain yield at three different growth stages of soybean. The experimental design was a randomized complete block of five treatments with nine replications. The deficit irrigation treatments im-posed were D1 (0 – 20 %), D2 (20 – 40 %), D3 (40 – 60 %), D4 (60 – 80 %) and D5 (80 – 100 %) of water deficit total available water (TAW). The three growth stages were flow-ering (49 DAS: days after sowing), seed growth (77 DAS), and maturity (140 DAS). The highest leaf N accumulation was in the D2 treatment at the flowering and seed growth stage. The soybean grain yield had positive significant cor-relation (p < 0.01) with leaf nitrogen at seed growth stage. Total nodule numbers at ≥ 4.75 mm diameter size had non-significant effect on leaf N accumulation, but had positive significant effect (p < 0.05) on grain yield of soybean at seed growth and maturity stage. On the other hand, total nodule numbers at < 4.75 mm size had positive signifi-cant effect (p < 0.01) on leaf N accumulation and grain yield of soybean at seed growth stage. Total nodule fresh and dry weight at ≥ 4.75 mm size had non-significant ef-fect on leaf N accumulation and grain yield of soybean, but nodules at < 4.75 mm size had a positive significant effect (p < 0.01) at seed growth stage. Individual nodule fresh and dry weight at ≥ 4.75 mm size showed negative signif-icant correlation (p < 0.01) with leaf N accumulation and grain yield, but nodules at < 4.75 mm size showed positive significant correlation (p < 0.01) at seed growth stage. Our studies demonstrated that the water deficit level D2 (20 – 40 % of TAW) was the best for an efficient Rhizobium-host association and subsequent nodule development. Based on our results, it can be concluded that successful root infec-tion of uninoculated soybean was more pronounced in < 4.75 mm diameter size class nodule than the larger ones (≥ 4.75 mm) under different water deficit levels.
