Chloride in soils

    Chloride exist in aqueous solutions as a monovalent anion and its salts are readily soluble.  Consequently, its is not adsorbed by organic matter or clay in most soils, and does not readily precipitate out of solution.  For these reason Cl is mobile in the soil and is readily leached where rainfall and/or irrigation exceeds evapotranspiration.   Chloride is one of the first elements removed from minerals by soil weathering processes.  This is why most of the world's Cl is found in oceans or in salt deposits left by evaporation from old inland seas.    

    Many soils and crops receive more than an adequate supply of Cl from sea spray carried by rain and snow.  This diminishs rapid with distance from the ocean.  Chloride deposition from rainfall may amount to 90 lbs/a per year along certain seashores (up to 5 miles inland), but decrease to < 18 lbs/ac per year 100 miles inland.  Midcontinental areas such as the Great Plains of North America typically receive < 0.9 lbs/ac (<1.0 kg/ha) annually through precipitation.

Chloride partitioning in mature wheat plant

    Wheat has the capacity to recovery a high percentage of the fertilizer Cl applied to the soil, particular at low testing sites.    A Montana study (Table 2) indicated 74, 60, and 59% of the applied Cl was recovered in the top growth at rates of 20, 40, and 80 lbs Cl/ac.  Normally only small quantities of Cl (< 3 lb/ac) are translocated to the grain, even under high yield (70 bu/ac) and soil Cl conditions.  The consequences of this are that a high percentage of applied Cl remains in wheat residue and is potentially available to subsequent crops, if the residue is not removed from the field site.

Residual effects of chloride applications

    Generalizations about the residual value of a single Cl fertilizer are difficult to make.  Many site-specific factors interact to influence the movement of Cl in the soil profile.   Wheat (Table 2 -above) and sugarbeets (Moraghan, 1987) studies illustrate that crops have the capacity to accumulate a large fraction of soil plus fertilizer Cl in their top growth.  Hence, a crop growing at a field site with appreciable Cl (e.g. 50 to 200 lbs/a) can result in considerable redistribution of soil Cl to the surface assuming the crop residue (e.g wheat straw and sugarbeet tops) are returned to the soil.  

Table 3.  Chloride partitioning in sugarbeet plants at five sites in the Red River Valley, North Dakota. 1985. Source:  Morghan (1987).
Parameter		Site A	Site B	Site C	Site D	Site E
		-------------------------------------- lbs Cl/a ----------------------------------------
Soil Cl (0-48")		196	294	109	120	53
	Tops	130	192	62	59	39
	Roots	11	18	8	4	7
Note: Soil Cl levels are based on samples collected during the fall 1984 (within 2 weeks of winter freezing).  Chloride contents in the tops and roots are based on plots fetilized with 150 lbs N/a.

    Residual effects of a single Cl fertilizer applications were examined by Schumacher and Fixen (1989) in a corn-wheat rotation.   Maximum Cl concentrations in the profile occurred at approximately 20" following the first growing season.    Also, greater than 50% of the fertilizer Cl was still located in the upper 48" of the profile (Table 4).    By the beginning of the third growing season, most of the fertilizer Cl had leached below 48" in the soil profile.