Nutrient Deficiencies and Toxicities Related to pH, Ca and Mg

Jarrod O. Miller, Extension Agronomist, jarrod@udel.edu and Cory Whaley, Sussex Co. Extension Ag Agent; whaley@udel.edu

We are observing a range of deficiency issues this year in corn, many of which have similar symptoms. Last week we had some images of a field with pale yellow leaves and some interveinal chlorosis that turned out to be a sulfur deficiency (https://sites.udel.edu/weeklycropupdate/?p=15087). This week we have similar symptoms, but a different diagnosis. Across this field (Figure 1), some corn appears pale and stunted, and upon closer inspection (Figure 2), there is also some stripping (interveinal chlorosis) along the leaves.

There are many nutrients that can cause interveinal chlorosis, and the most likely cause in Delaware is a lack of sulfur. However, zinc deficiencies can also be found in Delaware, but the stripes along the leaves can be wider and paler in color (https://www.agry.purdue.edu/ext/soilfertility/ZincDeficiencyCorn.pdf). Other nutrients that cause interveinal chlorosis in corn include iron (not likely in DE), magnesium (Mg) and manganese (Mn). Magnesium, a component of lime, is mobile in plant tissue, so the problem starts at the bottom of the plant, while Mn is not mobile, and issues will start at the top of the plant. In Figure 2, all the leaves have an issue, but the worst cases are at the bottom of the plant. Although Mg deficiencies are rare, they can be associated with low pH soils. Dolomitic limestone raises the pH while adding both Ca and Mg to the soil, therefore, low soil pH can also be associated with deficiencies in these two nutrients. A low soil pH can also cause metal toxicities, including aluminum and the micronutrients iron, manganese and copper.

In this field, soil and tissue tests point to a pH issue causing a multitude of nutrient problems:

  • Excess K in the tissue, while soil levels were not excessive. Low soil Mg will cause excessive K uptake.
  • Low Mg in the tissue due to low Mg in the soil.
  • Excessive Mn and Cu in the leaf tissue, while soil levels were in optimum ranges. The excessive micronutrients were due to the low soil pH (5.0), which allows greater uptake. The burned lower leaves may be a symptom of Mn toxicity.

All of these issues can be cleared up by liming the soil with a dolomitic limestone.

Figure 1. Pale yellow patterns like the S deficiency observed last week.

 

Figure 2. Leaves also have some interveinal chlorosis and yellowing at their edges, not typical for S deficiencies.

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