Evaluation of Soybean Genotypes for Iron-Deficiency Chlorosis in Potted Calcareous Soil

Iron-deficiency chlorosis in soybean [Glycine max (L.) Merr.] is a problem on some calcareous soils in the upper Midwest. Past attempts to screen soybean genotypes using potted calcareous soil from the field have not been successful. The objective of this research was to evaluate methods for screening soybean genotypes for Fedeficiency chlorosis in potted calcareous soil. Twelve soybean genotypes representing a range of resistance to Fe chlorosis were evaluated in potted calcareous soils taken from five locations in Minnesota and Iowa. Each soil was sieved and thoroughly mixed. Pots were prepared by packing soil evenly to a bulk density of 1.1 Mg m⁻¹. Soil water content was maintained constant by daily watering of undrained pots (bottom holes absent) to a specific weight, or by flooding greenhouse benches until the water level was 0.1 m below the soil surface in drained pots (bottom holes present). Second trifoliolate leaves were given chlorosis scores. The soil water content at which the most intense chlorosis occurred, differed for each soil. However, when gravimetric soil water content values were converted to matric potential values, the most intense chlorosis occurred within the range of -3 to -1 kPa, values slightly below saturation. Chlorosis scores of soybean genotypes when grown in pots were significantly correlated with field results in three out of four comparisons in the growth chamber and in one out of four comparisons in the greenhouse. Some soils that produce chlorosis in the field apparently do not produce chlorosis in pots. Significant differences in chlorosis scores and in some ranks were observed in the different soils. This is similar to what is observed in different field sites, however, the general classification of genotypes in the pots was the same as in the field.