A comparative study of soil solution chemistry associated with chlorotic and nonchlorotic soybeans in western Minnesota

Abstract

We planted three varieties of soybeans (Glycine max (L.) Merr.) with varying Fe‐ efficiency ratings (Swift, Hodgson, Anoka) across a high‐lime chlorotic spot in western Minnesota. Our objective was to determine the chemical components in soil solutions associated with chlorotic and nonchlorotic areas along transects through the chlorotic spot. We also measured soil temperature, soil moisture and bulk density along the transects. Chlorosis, determined by visual ratings and chlorophyll content, was associated with high CaCO₃(s) and mobile ion (i.e. Mg²+, Na+, Cl‐) accumulations at the edge of the depressional area. High soil solution Mg²+ (≈10 mM) and high plant Mg (1.5%) were consistently associated with low chlorophyll content, suggesting a possible causative relationship in reducing Fe²+ uptake. High Mg/Ca ratios (?1.8) in chlorotic areas were related to the over‐saturation of the soil solutions with respect to calcite. High HCO^‐ ₃ activities (8 ?M) correlated with chlorosis for one transect, but were not consistently related to chlorosis for the other two transects. High plant P correlated with chlorosis for all three varieties. Plant Fe was associated with soil contamination (aluminosilicate minerals) of leaves and not with chlorosis.

Key words:

• Iron chlorosis
• calcareous soils
• Mg/Ca ratio
• calcite
• Glycine max (L) Merr