Step-by-step guide to identify lacking micronutrients
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.
Take the detection process step by step, Ferrie says.
Diagnosis begins by knowing the symptoms of various deficiencies well enough to spot a problem. Determining whether symptoms appear at the top or the bottom of the plant eliminates half of the possibilities.
The Micronutrient Deficiency Detection Guide will lead you through the detection process. The first step is to rule out macronutrient (nitrogen, phosphorus and potassium) deficiencies, then evaluate micronutrient issues.
Micronutrients to Monitor
Here are capsule descriptions of the micronutrients most likely to cause problems, according to Farm Journal Field Agronomist Ken 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.
Copper deficiencies most often occur in high–organic matter soils (peats and mucks). Muck soils might need an annual application of copper.
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.
"High rates of phosphorus also will cause zinc deficiency," Ferrie says. "We see this where excessive manure has been applied and in sandy, calcaric soils. The deficiencies become more severe in cool, wet conditions."
Lights, Camera, Action
Photos of micronutrient deficiency symptoms, like the ones used on pages 20, 22 and 24, are almost impossible to find. That’s because it’s extremely difficult to get symptoms to manifest themselves the way you want them to for a portrait.
"It’s very hard to get one deficiency to show up," says Farm Journal Field Agronomist Ken Ferrie. "In the real world, you usually see several deficiencies at once."
That’s why Ferrie’s staff at Crop-Tech Consulting decided to create their own photos of micronutrient deficiencies. "We killed a lot of corn plants before we got the symptoms to show up," Ferrie says.
Thomas Zerebny took the lead, first finding nutrient mixtures and information about indoor lighting for plants. Two sources were especially helpful: Doug Walker of the University of California, Davis, and employees of the LaMotte Company of Chestertown, Md.
No one, though, had any experience growing corn hydroponically. After trying to grow corn in what the team thought was sterile, washed sand, very few deficiencies showed up. Soil testing discovered their sterile sand had more nutrients than most farmers’ fields.
Ultimately, with help from Ferrie’s son, Zach, Zerebny planted the corn in buckets, over lava rock, under grow-lights. Then he used an automated system to circulate the appropriate nutrient solution for each plant over its roots for 15 minutes out of every hour.