Chlorine and Plant Nutrition

• Chlorine has been noted as an essential plant nutrient since the 1950s, when T.C. Broyer and other researchers concluded several successful experiments involving artificially induced chlorine deficiency in test plants. Plants deprived of chlorine were found to exhibit wilt, discoloration and a variety of other symptoms not consistent with any other known plant disease. The role of chlorine in plants has been better understood since then, and chlorine uptake is now known to be an essential part of the chemical reactions that take place during photosynthesis. Chlorine also plays a role in plant cell hydration and cation transport.
  
  

Chlorine Absorption

• Chlorine (Cl) is absorbed by plants in its ionic form (CL-), typically found in soil solution. There are three ways in which chlorine is absorbed by plants: diffusion, root interception and mass flow. Diffusion is the movement of ions from high to low concentration in the water surrounding particles of soil. Diffusion occurs over very short distances. Root interception occurs when root growth at the cellular level contacts soil particles and absorbs ions, and mass flow is the water-induced movement of soil ions on a large scale. Mass flow occurs when dissolved ions in the soil are moved by irrigation, evaporation or rainfall.
  
  

Effect of Excess Chlorine

• Chlorine is found naturally in soil, in very small amounts, and has no adverse effects on plants at these levels. Problems can arise, however, when plants are irrigated with tap water, which is chlorinated by most municipalities. This can raise chlorine concentrations above levels safe for plants, and result in chloride toxicity. Leaf margins may appear scorched or reduced in size, with yellow mottling and increased abscission. Overall growth may be reduced or halted, and foliage may take on a thickened appearance.
  
  

Solutions

• Excess chlorine can be removed from water relatively easily. Tap water can be left out overnight to allow chlorine to diffuse out naturally, or it can be removed by boiling. Water should be boiled until the steam has no detectable chlorine aroma, and should be cooled before it is used to water plants. Excess chlorine can be avoided by using rainwater or distilled water, or by employing one of several commercially available filtration systems. Plants watered with distilled water should be given fertilizer as well, since prolonged use of distilled water can result in mineral deficiencies.