Forms of Chlorine

Chlorine is present in the soil solution primarily in the anionic form as chloride. Chloride concentrations in soil extracts may range from <1 mg kg^-1 to more than several thousand mg kg^-1 (68). Chlorine may also be present in organic forms such as chlorinated hydrocarbon pesticide residues. Some of these chlorine-containing molecules are recalcitrant, whereas others can be metabolized or mineralized to release the chlorine.

Although plants can accumulate chlorine foliarly and from the atmosphere, the concentration of chlorine in plant tissue is often closely related to the supply or concentration of chloride in soil. Testing soils for chloride is routine in laboratories involved in salinity problems, but soil testing for chloride supply to predict crop response to fertilization is a fairly recent development. Soil test interpretations for chloride supply are currently conducted in the North American Great Plains and are limited to only a few crops (2).

In this large land-locked geographical region, little potassium fertilizer (KCl) is applied, and chloride input from rainfall is low. Soil test interpretations for chloride have not been developed outside this region because chloride inputs from various sources are often greater and because supplies of this nutrient are generally considered adequate for most crops.