Soybean seedling root growth as influenced by soil texture, matric suction and bulk density

Laboratory experiments were conducted under controlled conditions to determine the effect of five matric suctions (0.05, 0.10, 0.30, 1.00 and 3.00 bars) and three bulk densities (1.10, 1.30 and 1.50 g.cm−3) on the moisture content, penetrometer resistance and soybean (Glycine max L.) root growth in six different soil textural groups (sand, silt, clay and their combinations). The different textural groups were compacted in PVC pipes 4.4 cm ID and 10 cm long and placed in pressure cells to obtain the desired matric suction. After equilibrium five pregerminated soybean seedlings were fixed on the soil surface. At the end of 48 hours root elongation was measured. There was an increase in root growth in all the textural groups at all the bulk densities when the matric suction was increased from 0.05 to 0.30 bar. There was however a gradual decrease in root growth as the matric suction increased from 0.30 to 3.0 bars. The reduction in root growth at low and high matric suctions was related to moisture content, change in soil resistance and redox status of the soil system. The measured penetrometer resistance values were directly related to the level of compaction, soil matric suction and also were dependent upon the texture. Close relationships were recorded between redox potentials and soil matric suction.