DIFFERENTIATING CHLORIDE SUSCEPTIBILITY IN SOYBEAN CULTIVARS

Fertilization with KCl can induce a Cl toxicity that decreases the yield of soybean [Glycine mar (L.) Merr.]. The objective of this study was to see if Cl toxicity can be avoided by selecting cultivars that take up less Cl from the soil. Sixty soybean cultivars, 12 each from Maturity Groups II, III, IV, V, and VI were grown on a Mexico silt loam (fine, montmorillonitic, mesic Udollic Ochraqualf) without added Cl or with 673 kg Cl ha-1 added as CaCl2. The addition of Cl increased the mean Cl concentration of all cultivars from 1.5 to 18.8 g Cl kg-1 at 15 d and from 0.4 to 1.3 g Cl kg-1 at 80 d. All 36 cultivars from MG II, III, and IV, along with 5 cultivars from MG V and VI, had significantly higher concentrations of Cl in leaves than did 19 cultivars from MG V and VI. Cultivars with high Cl concentrations were referred to as accumulators and those with low concentrations as excluders. The occurrence of leaf scorch, a symptom of Cl toxicity, in Cl accumulator cultivars was significantly higher than in Cl excluder cultivars. Leaf scorch ratings were positively correlated with Cl concentrations of soybean leaves at 15 and 80 d. Chloride concentrations in the leaves were higher (accumulators, 24.3 g kg-1; excluders, 7.0 g kg-1) at the early growth stages than in the later stages (accumulators, 1.8 g kg-1; excluders, 0.3 g kg-1). Addition of CaCl2 increased Cl concentrations in seeds of Essex, an accumulator cultivar, but had no significant effect on oil and protein content. The average grain yields of Cl accumulator cultivars were significantly decreased by 16% due to Cl addition, while grain yields of excluder cultivars were not significantly reduced. Cultivar selection in MG V and VI may be a means of minimizing Cl effects associated with muriate of potash fertilization.