Thirty Years of Chloride Trials in South Dakota Wheat.

Chloride (Cl-), the ionic form of Chlorine, has long been known to play an important role in plant development; critical in several different functions of osmoregulation within the plant. Despite its relatively low concentration requirements within the plant and its designation as a micronutrient, luxury consumption is common and Cl- concentrations in plants often range from 2,000 Ð 20,000 ppm. In South Dakota, significant research has focused on two aspects of how a Cl- deficiency might affect yields: 1) insufficient Cl- levels which affect plant functions including reduced photosynthetic capacity and water status or 2) Cl- effects on disease suppression. Much of this effort has been focused on spring and winter wheat with varying success of response, in part to the varied climate, which moves from humid continental climates in the eastern portion of the state to semi-arid in the west. The more humid east is far more likely to develop early-season disease symptoms and also soil Cl- deficiencies because of higher rainfall. Researchers at South Dakota State University made significant contributions to this work beginning in the 1980Õs. The benefits of Cl- were first noticed in spring wheat, which was shown responsive to KCl applications at sites with high levels of soil potassium. Follow-up research found that the critical Cl- level in plant tissue at head emergence was 1.5 g kg-1. For a soil correlation, Cl- levels above 43.5 kg ha-1 in the top 60 cm of soil were likely to result in the maximum yield response from wheat. This was later refined into interpretive soil test values. In more recent years, the response to Cl- has been far more variable particularly in drier climates. This work needs a continued effort to conclude in which climates Cl- applications can increase yields and remain economically viable.