Influence of FeEDDHA on iron-manganese interaction in soybean genotypes in a calcareous soil

Iron (Fe) deficiency is common in calcareous soils. Application of FeEDDHA is effective in correction of Fe deficiency in such soils. However, it may decrease concentration and uptake of some micronutrients including manganese (Mn). The effect of Fe on Mn status of different soybean [Glycin max (L.) Merr.] genotypes was studied in a greenhouse experiment in a completely randomized design with three replicates. The treatments consisted of three Fe levels (0, 2.5, and 5 mg Fe kg(-1) as FeEDDHA) and 12 soybean genotypes. Results showed that application of Fe increased top dry weight of Wells, Black hack, Elgin, and A3237, but decreased that of Steel and A3935 and had no effect on other genotypes. Addition of Fe increased concentration and uptake of Fe, but decreased that of Mn in all genotypes. The Fe: Mn ratio greater than 0.4 in plant tops when both Fe and Mn were in the nutrient sufficiency range were considered to be an indication of tolerance to Fe deficiency, as these genotypes did not respond to Fe fertilizer. Regression equations showed that the highest reduction of Mn concentration occurred at 2.5 mg Fe kg(-1). Manganese concentration was reduced by 13, 17, and 19% due to the dilution effect only in Black hack, A3237, and Elgin, respectively. Iron application did not cause either Fe toxicity in soybean or suppression in root: shoot ratio. it seems that Fe addition reduced Mn concentration in some soybean genotypes probably either by reduction of Mn concentration and/or translocation of Mn from root to shoot. The fact that soybeans are highly sensitive to Fe and Mn deficiencies and use of expensive FeEDDHA might accentuate Mn deficiency or imbalance in soybeans demonstrates a need to screen out and select soybean genotypes resistant to Fe stress.