Determination of Essentiality


Historical Information
  Determination of Essentiality
  Functions in Plants
Diagnosis of Chlorine Status in Plants
  Symptoms of Deficiency
  Symptoms of Excess
  Concentrations of Chlorine in Plants
    - Chlorine Constituents
    - Total Chlorine
    - Distribution in Plants
    - Critical Concentrations
    - Chlorine Concentrations in Crops
Assessment of Chlorine Status in Soils
  Forms of Chlorine
  Soil Tests
  Chlorine Contents of Soil
Fertilizers for Chlorine

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.).

Under the same conditions however, squash (Praecitrullus fistulosus Pang.) plants failed to exhibit any signs of chlorine deficiency. Species not affected or least affected by low chlorine supply appear to accumulate more chlorine than provided by the culture solutions. It has been assumed that chlorine was absorbed from the atmosphere and that plants differed in this ability (6,7). More recently, low-chlorine solution studies have produced chlorine deficiency symptoms in red clover (Trifolium pratense L.) and in wheat (Triticum aestivum L.) (8-10). Thus, the essentiality of chlorine has been established by the observations of the deficiency in a wide range of species.