Soil testing - background

    Historically, commercial soil testing laboratories have not included Cl analyses as part of their testing and fertilizer recommendation programs.   Prior to the 1980's, it was generally believed that Cl deficiency was unknown in the field and that crops would not benefit from application of Cl containing fertilizer.  Oregon studies (Taylor et al., 1981; Christensen et al., 1981) provided some of the first evidence that field grown crops (e.g. wheat) could benefit from Cl fertilization.  In one study, soft white winter wheat yields fertilized with NH₄Cl exceeded (NH₄)₂SO₄ by 1110 lbs/acre average over 3 sites.  Later, spring wheat studies in South Dakota demonstrated yield responses to KCl fertilization were due to the Cl component in this fertilizer (Fixen et al., 1986a).   Today, there appears to be little doubt that field grown crops can benefit from Cl applications.   Soil Cl testing has been identified as potentially useful tools in Cl response prediction in South Dakota (Fixen et al., 1986b) and Montana (Engel et al., 1998).   While commercial soil Cl testing is still not common, it has begun to be adopted by commecial laboratories serving wheat producers in the Great Plains region.