Early observations of plant growth responses derived from the use of chlorine-containing fertilizers
had suggested that chlorine was at least beneficial if not essential (5)
. Demonstrating the essentiality
of chlorine is experimentally challenging because chlorine is present widely in the environment, and
special precautions are necessary to remove chlorine from chemicals, water, and air to induce
deficiency symptoms in most species (6)
. Solution culture experiments conducted in a relatively chlorine-
free environment (1)
provided the first recognition of chlorine as an essential microelement.
These experiments further showed that chlorine deficiency symptoms were alleviated specifically by
the addition of chloride. Using solution culture (7)
, acute chlorine deficiency or at least restricted
growth was demonstrated in lettuce (Lactuca sativa L.), tomato (Lycopersicum esculentum Mill.), cabbage
(Brassica oleracea var. capitata L.), carrot (Daucus carota L.), sugar beet (Beta vulgaris L.), barley
(Hordeum vulgare L.), alfalfa (Medicago sativa L.), buckwheat (Fagopyrum esculentum Moench),
corn (Zea mays L.), and beans (Phaseolus vulgaris L.).