AGRI-BRIEFS
  AGRONOMIC NEWS ITEMS 		From Agronomists of the
Potash & Phosphate Institute
655 Engineering Drive, Suite 110
Norcross, Georgia 30092-2837
Phone (770) 447-0335

Winter 1998, No. 7

IS YOUR WINTER WHEAT LACKING CHLORIDE?

Chloride has been recognized as an essential plant nutrient since the 1950s. Response of wheat to chloride fertilization has been observed throughout the Great Plains from Texas to Canada. Yield increases from chloride fertilization in this region are common because of low atmospheric chloride deposition and the relatively infrequent use of chloride bearing fertilizers.

Chloride is involved in several important roles in plants, including,

Chloride is an anion and is therefore mobile in the soil. It may be leached from the soil profile where internal soil drainage is good. Also, in areas where muriate of potash (KCl) fertilizer has not been regularly applied, chloride deficiencies may occur. Atmospheric chloride deposition tends to be rather high along coastal regions and decreases inland, making the likelihood of response higher in the central part of the country.

Increases in wheat yield from chloride fertilization are usually associated with the correction of chloride deficient conditions or suppression of fungal diseases. Under low soil chloride conditions some varieties may exhibit chloride deficiency symptoms, sometimes referred to as physiological leaf spot syndrome. These symptoms are similar in appearance to tan spot or septoria but are not caused by a pathogen. The absence of leaf spotting does not always mean that chloride is not deficient since spotting is dependent upon wheat variety. Chloride has been shown to reduce the severity of several root and foliar diseases. In one Texas study leaf rust infection of the flag leaf was reduced from 68 to 27 percent by topdressing with 40 pounds of chloride per acre as muriate of potash.

Research has shown that where wheat responds to chloride fertilization the average response is just over 5 bushels per acre, although yield increases as high as 23 bu/A have been observed. Whether or not wheat will respond to chloride usually depends upon soil chloride level, disease pressure, plant chloride, and variety. Response to chloride is likely when soil chloride levels are less than 30 pounds per acre from 2-foot deep soil samples. The optimum level of soil chloride is at least 60 pounds per acre-2 feet. Continuing research has shown that some varieties consistently respond to chloride and some do not. For example, Kansas studies have shown that under low soil chloride conditions Karl 92, 2163, and Jagger consistently respond to chloride topdressing while Ogallala does not.

Chloride is not a "magic bullet". It is one of 17 nutrients essential for proper plant development and function. Where conditions such as low soil chloride levels or high disease pressure exist, chloride can be a profitable component of a wheat fertility management program.


—WMS—

For more information, contact Dr. W.M. (Mike) Stewart, Great Plains Director, PPI, P.O. Box 6827, Lubbock, TX 79493. Phone: (806) 795-3252. E-mail: mstewart@ppi-far.org.
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