Root aeration inhibits the recovery of soybean from flooding-induced chlorosis under non calcareous conditions

Effects of aeration of flooded rooting medium (quartz sand) on the Fe mobilization and the chlorosis of soybean (Glycine max Merr, L. cv. A7) were investigated. Control plaits grown on well-drained sand mobilized enough Fe from sand and stayed green during the entire experiment. Flooding of the rooting media, irrespective of roots being aerated or not, caused the top 2-3 trifoliate leaves of soybean to tum chlorotic. The lowest chlorophyll concentration of these leaves was reached ca. nine days after commencement of flooding. Leaves of soybean whose roots were flooded, but not aerated, gradually recovered from chlorosis (regreened). By the 37th day, the newly formed leaves contained the same concentration of chlorophyll as the control plants. Leaves of soybean, whose roots were flooded and also aerated, contrary to expectation, never recovered from chlorosis. Also leaves formed by these plants after the onset of flooding were more chlorotic when compared with the flooded and unaerated plants. No clear relation could be detected between the concentrations of Fe, P, K, Ca, Mg, and Mn in the leaves, and the development of, or recovery from chlorosis. These observations along with similar observations by others under calcareous conditions indicate that an insufficient oxygen supply to the roots may not be the direct cause of leaf chlorosis under flooded conditions.