Influence of Artificially Restricted Rooting Depth On Soybean Yield and Seed Quality Under Field Condition.

The amount of plant available soil water is strongly influenced by soil type and rooting depth.  This study was conducted to investigate the influence of limited plant available soil water on soybean yield and seed composition.  Six soybean cultivars were grown in 2007, 2008, and 2009 on a field with plastic liners inserted at depth of 0.3, 0.45, 0.6, 0.75, and 0.9 m to limit the rooting depth and the amount of plant available soil water.  Distinct differences in amounts and distribution of rainfall were observed among the three years (290, 675, and 440 mm in 2007, 2008 and 2009, respectively).  Significant differences in yield and seed composition were observed among years.  However, within a rooting depth, cultivar and cultivar × year interactions were generally not significant.  The yield, oil content, and individual seed weight were the lowest and the protein and saturated fatty acids (C₁₆ and C₁₈) were the highest in 2007 compared to the other two years. These changes were greater in the plants grown at restricted rooting depth. The yearly precipitation during reproductive stage was more closely correlated with soybean yield and seed quality compared to whole-season precipitation. Results from 2008, demonstrated that the impact of limited rooting depth on soybean yield and seed quality is do to limited water availability.  Results presented in this study illustrate that artificially limiting rooting depth under field conditions may serve as a cost effective means to manipulate plant-available soil water to study selected plant responses to water deficit stress.