Iron Supply in Soybean Seedlings1

Soybean [Glycine max (L.) Merrill] seedlings are dependent on the iron supply in the seed for early growth. Any factor that limits this supply of Fe could cause poor growth and would require management practices to eliminate these factors to insure good seedlings. Phosphate and Fe‐stress response were the variables used to test the availability of seed iron in the seedlings. Phosphate competes with the plant for Fe, and Fe‐stress response is an adaptive mechanism that accentuates the transport of iron. ‘PI‐54619‐5‐1’ (PI) soybean has an inefficient Fe‐stress response mechanism and ‘Hawkeye’ (HA) has a very efficient Fe‐stress response mechanism. Our objective was to determine how these factors affected the utlization of Fe from the soybean seeds as compared to Fe supplied externally. Soybean seeds of these two lines were produced by plants treated from anthesis to seed maturity with 59Fe supplied as ferric ethylenediaminedi(o‐hydroxyphenylacetate). Seedling plants, from labeled 59Fe seeds, were subsequently studied to determine the effect of Fe‐stress response and to determine the effect of varied nutrient P on the translocation and utilization of 59Fe from the cotyledons of Fe‐inefficient and Fe‐efficient soybeans. Cotyledonary Fe, of both lines in the seedling stage, appeared available for translocation and utilization and was not affected by Fe stress or varied nutrient P. It was concluded that Fe should not be a limiting factor in establishing a good stand of soybeans in the field because of the readily available source of Fe from the seed.