Nutrient‐solution techniques for evaluation of iron efficiency of soybean1

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Abstract
The iron (Fe) efficiency of soybean [Glycine max (L.) Merr.] genotypes generally has been evaluated in the field on calcareous soil. A nutrient‐solution system has been developed to permit evaluation of Fe efficiency throughout the year. The objectives of this study were to assess the effectiveness of nutrient‐solution tests for evaluating the Fe efficiency of soybean genotypes and to evaluate alternative nutrient‐solution techniques that could minimize the cost of labor and chemicals. Five bicarbonate (HCO3 ‐) concentrations and three solution‐change schedules were evaluated in a factorial arrangement. Eight soybean genotypes with a wide range of Fe efficiency were evaluated in each treatment and in replicated field tests on calcereous soil during 3 years. Rank correlation coefficients between mean chlorosis scores of genotypes in nutrient solution and field tests ranged from 0.81 to 0.91 for the three solution‐change schedules and from 0.85 to 0.89 for the five HCO3 ‐ concentrations. Replacing the solution every 4 d was not superior to replacing it only at each stage of plant development or not changing the solution throughout the test. A stepwise increase in HCO3 ‐ level at each stage of plant development was not superior to utilizing a constant level of HCO3 ‐ throughout the test. The most economical evaluation of the Fe efficiency of soybean genotypes in nutrient solution can be achieved with no change in the solution and one or more HCO3 ‐ levels that are held constant throughout the test.