The following information is a Web Extra from the pages of Farm Journal. It corresponds with the article "Micronutrients Can Have a Macro Impact” by Darrell Smith. You can find the article on page 27 in the September 2010 issue.
Here are sources of papers about manganese authored by persons featured in this article:
Other Micronutrients to Watch
Manganese is just one of the micronutrient deficiencies that growers need to watch for, says Ken Ferrie, Farm Journal Field Agronomist.
“Behind manganese, iron is the most common micronutrient deficiency,” says Ferrie. “It occurs most often on poorly drained or high-pH soils. Iron deficiency often shows up in the soil with a high manganese content. As with manganese, deficiencies can be induced by over-liming.”
Symptoms can be confused with manganese deficiency, Ferrie notes. “Areas between the leaf veins turn light green, yellow or almost white,” he says. “With manganese deficiency, the symptoms occur over the entire plant. With iron deficiency, the symptoms are found only on the younger leaves, on the top of the plant. From the road, the entire field looks yellow; but, in reality, it’s only the new growth.”
Symptoms of iron deficiency sometimes show up when soil has been saturated by rain, and then disappears when the field dries out.
Like manganese, iron deficiency usually occurs because the nutrient is tied up in the soil, unavailable to plants. So foliar applications, rather than soil treatments, are required.
Less common are deficiencies of zinc, boron, sulfur and molybdenum.
“Zinc deficiency is characterized by interveinal yellowing on the younger leaves of soybeans,” Ferrie says. “The leaves take on a bronze or gray cast, because of the dead leaf tissue, as the plants mature. It usually occurs in high-pH soils with high phosphorus levels, such as fields that have received excessive amounts of manure.”
Boron deficiency causes shortened internodes and yellowing or reddening of the upper leaves. It usually shows up on sandy soils during dry conditions, especially if the soils have been over-limed. “Be very careful with lime applications in light soil,” Ferrie cautions. Boron deficiency also can occur if soybeans follow alfalfa, which is a big user of the nutrient.
Like iron, zinc and boron can be foliar-applied. Boron and zinc also can be applied in dry fertilizer.
“Molybdenum deficiency usually occurs in soils that have become highly acid because of weathering or leaching,” Ferrie says. “It causes poor nodulation, so soybean plants have difficulty producing nitrogen. Usually, you can correct the deficiency by applying lime.”
Sulfur deficiency causes newly emerged leaves to take on a pale yellow-green color, which disappears after a few days. “And the stems will be thinner than you would expect,” Ferrie says.
It can result from low sulfur levels in the soil; wet, cool soil conditions, which slow the release of sulfur from the organic form; leaching of sulfur from sandy soils; and soil acidity, which reduces microbial activity. Sulfur fertilizer is available in various forms.
Diagnosis of micronutrient deficiency symptoms can be challenging. “Soil tests can be useful, but they are not as accurate as the tests for nitrogen, phosphorus and potassium,” says Ferrie. “Various laboratories use different extraction procedures, so you must understand the meaning of high, medium and low as used by your lab.
“Tissue analysis is the most accurate method of diagnosing deficiency symptoms,” Ferrie concludes. “If you spot symptoms in your field, send in a tissue sample, and make sure you’re treating the correct deficiency.”
To see photos of iron, zinc, boron, sulfur and other deficiency symptoms, go to:
- September 2010