EFFECTS OF PROLONGED FLOODING ON SOYBEANS DURING EARLY VEGETATIVE GROWTH1

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Abstract
Prolonged flooding is usually harmful to cultivated plants and has been found to reduce plant growth and development. There is a need to evaluate the effects of prolonged flooding on soybean [Glycine max (L.) Merrill] development, especially during early growth stages. A greenhouse study investigated the effects of prolonged flooding at V1 and V4 growth stages of soybeans grown on Crowley silt loam, emphasizing the root parameters. The porous membrane root-culture technique was used to enable recovery of the intact root system of each plant. Forrest soybeans were subjected to a 7-d flood at V1 and V4 growth stages. The flood height was maintained at 2.5 cm. Root length, area, nodulation count, and dry weight and shoot dry weight were measured just before the flood and 7 and 14 d after the flood. Plant heights and number of leaves per plant were evaluated every other day. Prolonged flooding significantly reduced all soybean root and shoot growth parameters. Linear relationships with positive slopes were found between root extension, root area, and root weight. Flooding at V1 completely inhibited root nodulation. The shoot:root ratio, which was greater at V4 than at V1 for the flooded and the controls, increased with time after flooding for both growth stages. Seven days after the flood was removed, the shoot:root ratio was significantly lower in the soybeans that had been flooded than in the controls.