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Soybeans micronutrients: Chloride

Soybeans micronutrients: Chloride

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Welcome to the part three of the soybean micronutrients column series. The last two weeks I introduced the series and discussed boron. I will cover how chloride is essential to soybeans, known deficiencies and toxicities in the region, factors of chloride availability in soil, soil and plant tissue testing, and chloride fertilizer recommendations. One good regional publication that addresses chloride is called Micronutrients for Soybean Production in the North Central Region.

In soybeans, chloride is needed for osmotic regulation in plant cells and is mobile from old to new tissue. Deficiency symptoms are very rare because soybeans are one of the least sensitive crops we grow. Deficiency symptoms are not evenly clearly described but may include chlorosis and wilting of leaves. However, toxicity is more of a problem in soybeans in some production areas and symptoms include leaf tip scorching, premature yellowing or bronzing of leaves, and leaf loss. Chloride is a monovalent anion (Cl-) found in soil solution which is unique among other micronutrients. Chloride is weakly held in soil and can be leached with high rainfall and irrigation. Availability in the soil each year is regulated by inputs including chloride in rainfall, irrigation water, fertilizers like potash (potassium chloride), crop residue/organic matter, and salts found in saline soil. Chloride deficiencies are not a concern in soybeans, but could occur in winter wheat, sorghum, or corn. Deficiencies would more likely to occur on rainfed sandy soils where potash fertilizer is not used.

Soil sampling and interpretations for chloride in the top two feet are used for other crops more sensitive to deficiency like winter wheat. Since toxicity is more commonly a problem in soybeans, researchers have found that soybean plant tissue nutrient analysis can be used to determine potential chloride toxicity problems. Soybean chloride sufficiency is best determined during full bloom to early pod set, typically in early July. The uppermost fully expanded trifoliolate without the petiole from 30 random plants should be sent to the lab in a paper bag. The chloride sufficiency range is 200 to 1400 ppm or 0.02 to 0.14 percent. Soybean varieties are categorized by seed companies in areas where chloride toxicity is an issue as chloride “includers” or “excluders”. Research in Arkansas found that concentrations high enough to cause a 5% yield reduction was 1885 ppm for chloride excluders and 3923 ppm for includers. The addition of chloride fertilizer would more likely cause yield losses in chloride includers. Companies have not rated most varieties in the Midwest since chloride toxicity is not normally a problem.

Do not target chloride fertilizer applications to soybeans in southeast Nebraska. If your fertility program calls for potash, I would suggest applying it prior to corn, sorghum, or wheat. There are some high chloride irrigation water concentrations in southeast Nebraska with the highest levels found in Jefferson County. You may want to collect irrigation water samples on your farm to determine chloride concentrations.

Feel free to email me at nathan.mueller@unl.edu or call me at 402-821-1722 to submit a question about micronutrients. I looked forward to writing about cobalt in my next biweekly column. Know your crop, know your tech, know your bottom line at croptechcafe.org.

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