Soil Chemical Factors Associated with Soybean Chlorosis in Calciaquolls of Western Minnesota1

Abstract

AbstractIron chlorosis in soybean [Glycine max (L.) Merr.] is a significant problem in calcareous soils of the upper Midwest. Field studies were established during 1983 in western Minnesota on two sites containing calcareous soils and one site containing gypsic‐calcareous soil (Typic Calciaquolls) to evaluate the soil chemical properties associated with iron chlorosis in soybean. Chlorosis was correlated with increases in soil solution bicarbonate (HCO−3) at the two calcareous sites, but not at the gypsic‐calcareous site. Chlorosis was correlated with increases in total calcite (CaCO3) at all sites. Higher concentrations of soil solution Ca2+ and SO2−4 were found at the gypsic site as a result of greater gypsum (CaSO4. 2H2O) solubility relative to CaCO3 solubility. However, because both CaCO3 and CaSO4. 2H2O were correlated with chlorosis at this site it was difficult to determine which may have been the most important causal factor. Concentrations of mobile soil solution ions such as K+, Na+, Mg2+, and NO−3 were generally greater in chlorotic areas of all sites as a result of accumulation in lower landscape positions associated with chlorosis. Seed yields were correlated with chlorophyll contents measured in the third trifolioliate leaf stage (V4) and during flowering (R1). Chlorosis ratings ranging from 2.5 to 5 resulted in 35 to 40% yield reductions for each unit chlorosis rating (1–5 scale). Increases in plant tissue K, Ca, Mg, Cu, Zn, Mn, and B were associated with increases in chlorosis for all cultivars at all sites. These increases may have been due to a combination of factors including ion balance, concentration of elements in stunted plants, and contamination of chlorotic tissue by soil.