DIFFERENTIATING CHLORIDE SUSCEPTIBILITY IN SOYBEAN CULTIVARS

Fertilization with KCl can induce a Cl toxicity that decreases the yie ld of soybean [Glycine mar (L.) Merr.]. The objective of this study wa s to see if Cl toxicity can be avoided by selecting cultivars that tak e up less Cl from the soil. Sixty soybean cultivars, 12 each from Matu rity Groups II, III, IV, V, and VI were grown on a Mexico silt loam (f ine, montmorillonitic, mesic Udollic Ochraqualf) without added Cl or w ith 673 kg Cl ha-1 added as CaCl2. The addition of Cl increased the me an 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 significantl y higher concentrations of Cl in leaves than did 19 cultivars from MG V and VI. Cultivars with high Cl concentrations were referred to as ac cumulators and those with low concentrations as excluders. The occurre nce of leaf scorch, a symptom of Cl toxicity, in Cl accumulator cultiv ars was significantly higher than in Cl excluder cultivars. Leaf scorc h ratings were positively correlated with Cl concentrations of soybean leaves at 15 and 80 d. Chloride concentrations in the leaves were hig her (accumulators, 24.3 g kg-1; excluders, 7.0 g kg-1) at the early gr owth stages than in the later stages (accumulators, 1.8 g kg-1; exclud ers, 0.3 g kg-1). Addition of CaCl2 increased Cl concentrations in see ds of Essex, an accumulator cultivar, but had no significant effect on oil and protein content. The average grain yields of Cl accumulator c ultivars were significantly decreased by 16% due to Cl addition, while grain yields of excluder cultivars were not significantly reduced. Cu ltivar selection in MG V and VI may be a means of minimizing Cl effect s associated with muriate of potash fertilization.