A to Z of Crop Nutrients: Copper (Cu) and Chloride (Cl)

Chloride (Cl) is taken up by the plant in the Cl- form. Because soil is negatively charged, Cl- can be mobile and leach in soils. Cl- is thought to be a driver in stomatal regulation, which helps control water levels in the plant. Therefore it is an important element in helping regulate water loss and moisture stress. It is also believed to be important in the internal plant transport of potassium, calcium and magnesium.

For the most part some vegetable crops as well as alfalfa and some small grains tend to be higher responders to chloride. There are types of soybeans called excluders that can more or less hold Cl- in the root system and not allow it to be transported into the tissue to damage the plant. Includer soybean varieties will transport the Cl- into the plant tissue, and as a result show injury. Because Cl- is so mobile, in areas where the issue exists, high natural rainfall and good drainage can aid in moving the Cl- down and out of the soil profile.

Copper (Cu) can be found in the cation form Cu+ or Cu++ and is thought to be one of the more tightly held micronutrients in your soil. It performs many functions in the plant, including chlorophyll formation and a number of important enzyme systems. Copper availability decreases at higher pH levels and can be held more tightly in organic matter. So, if you have high pH/high organic matter pockets on your farm it could be possible to see Cu deficiencies.

In my opinion both soil and tissue testing are good practice when trying to diagnose an issue such as a Cu deficiency. Other metal elements like Zn and Mn can impact the availability of Cu, so a soil test in addition to a tissue test can help discern potential issues. High phosphorous levels in heavily manured fields can also limit Cu availability. Like Cl- ,crops that tend to be more responsive to Cu include many of the vegetable crops but Cu deficiencies can also occur in wheat. Cu can easily be applied if you do have a deficiency but over-applying can create some toxicity issues.

Next week we will tackle Iron and Molybdenum.