Trifoliolate Leaflet Chloride Concentrations for Characterizing Soybean Yield Loss from Chloride Toxicity

Chloride includer soybean cultivars are more susceptible to chloride toxicity than excluder cultivars. The critical tissue chloride concentration defining toxicity is lower for excluder cultivars. Yield loss from chloride toxicity can be predicted by tissue analysis.Chloride toxicity is a yield limiting problem for soybean [ Glycine max (L.) Merr.] production, but limited information is available to accurately diagnose and manage Cl toxicity. The research objective was to determine how incremental additions of Cl affect the yield of Cl excluder and includer cultivars and develop critical leaflet‐Cl concentrations that indicate when yield loss from Cl toxicity begins. Six soybean cultivars, three Cl‐includer and three Cl‐excluder cultivars, were planted at five site‐years. Chloride solution containing CaCl 2 ∙2H 2 O and MgCl 2 ∙6H 2 O salts was applied to the soil surface beginning at late vegetative growth with final rates ranging from 0 to 1010 kg Cl ha −1 . Tissue Cl concentration was measured by sampling trifoliolate leaflets during reproductive growth. Critical leaflet‐Cl concentrations at the R3 stage were developed by regressing relative soybean yield across leaflet‐Cl concentration for each cultivar Cl rating. Chloride addition reduced soybean seed yield, on average, by 17% for Cl includer and 5% for excluder cultivars. Leaflet‐Cl concentration explained 56% of the variability in relative grain yield for Cl excluders and includers. Relative seed yield declined linearly at 2.6% (1000 mg Cl kg) −1 for cultivars within each Cl rating group with 5% yield loss expected when concentrations exceeded 3923 mg Cl kg −1 for includers and 1885 mg Cl kg −1 for excluders. The ability to predict when potentially toxic amounts of Cl are taken up using tissue analysis is the first step in developing management strategies that may help mitigate yield loss.