9 Chlorine 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. | 6 30 2006 4 12 PM Page 279 9 Chlori ne Joseph R. Heckman Rutgers University New Brunswick New Jersey CONTENTS Historical Determination of Functions in Diagnosis of Chlorine Status in Symptoms of Symptoms of Concentrations of Chlorine in Plants .283 Chlorine Total Distribution in Critical Chlorine Concentrations in Assessment of Chlorine Status in Soils .285 Forms of Soil Chlorine Contents of Fertilizers for Application .287 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 . This chapter however is concerned primarily with chlorine as a plant nutrient. 279 6
