Abstract:
A green house experiment was conducted at Dejen, Northwest Ethiopia, with the objective of quantifying the critical soil water deficit and P levels that affect yield and yield components of soybean,
and determine the critical soil water deficit levels influencing P uptake in soybean. The treatment
consisted of factorial combination of four available soil water (ASW) deficit levels (0%, 25%, 50%
and 75%) and four levels of phosphorus (0, 10, 20, and 30 kg∙ha−1) laid out in RCBD with four replications using soy bean variety Jalale as a planting material. The experiment was conducted under green house condition at Dejen, South Ethiopia during the 2011 academic year. Air dried soil
was filled in the pots and seeds were sown on May 13, 2011. Four plants were maintained on each
pot after thinning till flowering but after flowering, the total number of plants per pot was reduced
to three as one plant which was used for measurement of root biomass. The water deficit treatments were imposed after the plants have been fully established 2 weeks after emergence just before branching stage. The water deficiency was imposed through maintaining the soil moisture
content below field capacity at the deficit levels of 25%, 50% and 75%. The 75% of ASW deficit
resulted in the longest days (45) to flowering and maturity (99) compared to the 0%, 25% and
50% deficit levels. Also, the 75% of ASW deficit level resulted in shorter plants (55 cm), the lowest
leaf area (82.6 cm2), the highest root to shoot ratio (0.0168) and the lowest DM accumulation
(161.3 gm−2) compared to the other ASW deficit levels. Likewise, the 75% of ASW deficit level gave
the lowest number of pods per plant (4.13), seeds per pod (1.69), 100 seed weight (2.54 g), seed
yield (13.4 g∙m−1), above ground biomass (174.6 g∙plant−1) and harvest index (0.08) compared to
the other ASW deficit treatments. The degree of sensitivity to drought increased dramatically
(from 0.0423 at 25% to 0.9604 at 75%) with increase in water deficit level. Tissue analysis results
indicated that the highest seed P concentration (1.285%) and uptake (432.5 g∙plant−1) were ob
