GROWTH OF SOYBEANS AT DIFFERENT SOIL MATRIC POTENTIALS

Abstract

ABSTRACT

In a greenhouse study, we determined the optimum level or range of soil matric potential (SMP) for rapid, early-season soybean growth and development. Sharkey clay (Vertic Haplaquept, very fine, montmorillonitic, thermic) and Dubbs silt loam (typic Hapludalf, fine-silty, mixed, thermic) surface soils were equilibrated before planting to SMPs of near –0.3, —0.4, —0.5, —0.6, and —0.7 bar, as measured with tensiometers inserted into individual plastic pots. The plant water status resulting from the SMPs was evaluated by measurement of xylem pressure potential (PP). At 35 days after planting, plants were harvested, and dry weights of leaves, stems, and roots were determined. Leaf area index (LAI) and shoot-root ratios were calculated, and nodes/plant and plant height were also measured.

Shoot weights and LAIs of plants growing in soils with —0.3, —0.4, and —0.5 bar SMP did not differ, but both declined significantly at —0.6 and —0.7 bar SMP. Root density values in the —0.3− to —0.6-bar SMP range were not significantly different, but were significantly higher than the value measured at the —0.7-bar SMP. The amount of shoot mass supported by a unit of root mass progressively declined as SMP decreased. The Sharkey clay supported more shoot dry matter and leaf area production than did the Dubbs silt loam at all SMPs of the study. This was attributed to a more favorable water status of the plants growing in the Sharkey clay, as determined from the PP measurements. The results of this study indicated that for the most rapid vegetative growth and development of soybeans, SMP should be kept above —0.6 bar.