Historical Information

Chlorine is classified as a micronutrient, but it is often taken up by plants at levels comparable to a macronutrient. Supplies of chlorine in nature are often plentiful, and obvious symptoms of deficiency are seldom observed. In many crops it is necessary to remove chlorine from air, chemicals, and water to induce symptoms of chlorine deficiency. Using precautions to establish a relatively chlorine-free environment, Broyer et al. (1) was able to convincingly demonstrate that chlorine is an essential nutrient. Although crop responses to chlorine applications in the field were suspected as early as the mid-1800s, it was not until fairly recently that chlorine was considered a potentially limiting nutrient for crop production under field conditions. In the 1980s, the responsiveness of some crops to chlorine fertilization became recognized more widely (2). Even though chlorine has gained the attention of agronomists, much of the focus on chlorine in terms of crop production continues to be over the presence of excess levels of chloride salts in soils, water, and fertilizers (3,4).