A Review of the Effects of Chloride Inclusion/Exclusion On Soybean Yield in Arkansas.

Information regarding soybean [Glycine max (L.) Merr.] tissue chloride (Cl) concentrations and the value of selecting a Cl-excluding variety in high Cl environments is lacking. Our objectives were to propose a tentative, critical trifoliate leaf Cl concentration for diagnosing Cl toxicity, and show evidence that Cl-excluding varieties are beneficial in high Cl environments. A critical leaf Cl concentration was determined by regressing relative soybean yields (%RY) and trifoliate leaf Cl concentrations (R3-R4 stage) from published data. Soybean yields from University of Arkansas yield trials conducted at the same four sites from 2010 to 2012 were numerically compared by categorizing each variety as a Cl excluder or includer. A significant linear relationship [%RY = 108 – 0.0039x, r² = 0.79 where x = leaf Cl concentration (mg Cl kg^-1)] for Cl-including varieties was derived using published mean yield and leaf Cl results. The preliminary relationship suggests soybean yields will be reduced when leaf Cl concentrations exceed 3500 mg Cl kg^-1. Variety trial results from the Rohwer site in Southeast Arkansas showed that the mean yield of maturity group 5.0-5.5 Cl-excluder varieties (3468 kg ha^-1) was numerically greater than yields of Cl-includer (3161 kg ha^-1) varieties in all three years. No other site showed a consistent trend for Cl-includer or –excluder varieties to produce consistently greater yields than the other.  The Rohwer site is known to have high Cl concentrations in the irrigation water and demonstrates the importance of variety selection for high Cl environments.