Micronutrients are essential for plant health. You can apply a micronutrient mix that, you hope, will prevent problems or you can learn to identify the symptoms and treat only if you find a problem. Farm Journal Field Agronomist Ken Ferrie recommends the latter approach.
"Micronutrient deficiencies can be serious—if you have them," Ferrie says. "But problems with micronutrients usually are driven by some other condition, such as compaction, drought, organic [muck or peat] soils, sandy soils and acid or alkaline soils. If possible, solve the micronutrient issue by fixing the underlying cause.
"The environment tells us where to expect micronutrient issues," he adds. "Elsewhere, it’s rare to find a problem."
Neither crop scouting, soil testing nor tissue testing is sufficient, by itself, to diagnose a micronutrient deficiency. It requires a combination of all three.
Here are capsule descriptions of the micronutrients most likely to cause problems, according to Ferrie.
Boron is involved in cell division, viability of pollen grains, and the formation and metabolism of carbohydrates. But its biggest impact is on water metabolism. "If boron availability in the plant is low, it can have trouble taking up water," Ferrie says.
Boron deficiency also can be triggered by excess potassium and calcium in the soil. Deficiency symptoms in plants are difficult to identify because the individual symptoms mimic those of other nutrients.
Symptoms include scattered white spots between the veins on the youngest leaves, which eventually form 2" or 3" long stripes. Plants will have shortened internodes, difficulty unfurling the whorl and rippling at the leaf edges. On older leaves, you will see scorching along the edges. At harvest time, you will find banana-shaped, poorly filled ears.
Copper affects chlorophyll formation and enzymes involved with photosynthesis and disease resistance. Because it plays a role in the development, release and survival of pollen, it is
important when crops pollinate under stress. Under severe copper deficiency, plants might die midseason. It can be mistaken for seedling blights.
Iron affects the chlorophyll and respiration processes. "In acid soils, iron availability increases during times of excessive rain and poor soil aeration," Ferrie says. "But in alkaline, calcareous soils, excessive wetness causes iron deficiencies. In muck soils, high levels of iron result in manganese deficiency."
Tissue and soil tests usually are poor indicators of iron levels, Ferrie adds.
Manganese affects chlorophyll production and metabolism of carbohydrates and nitrogen. Deficiencies are most common in soils with pH above 5.8. They commonly occur in alkaline, extremely sandy and organic soils.
Manganese and iron influence each other, and the effects vary by soil type. "In alkaline soils, high levels of manganese will reduce uptake of iron," Ferrie says. "But if high-organic muck soil gets too acid, enough iron will come into solution and cause manganese problems."
In extremely acid organic soils, apply lime to correct the manganese deficiency. Don’t over-lime mineral soils or you will cause manganese deficiency. For immediate results, make a foliar application. You might need two, since manganese, like iron, does not move in the plant, so new growth that emerges after spraying might still be manganese-deficient.
Zinc plays a role in protein synthesis, development of floral parts and grain and seed production. Deficiencies are most common in badly eroded soils, high-pH soils, cool, wet soils and compacted soils.
This article first appeared in Farm Journal in 2012.