No simple solution to micronutrient management

Some days, it seems I get more questions about micronutrients and their management in crops than any­thing else—and not without reason. They are the least understood and most often ignored nutrients.

While micronutrients are abso­lutely critical for plant growth and optimum yields, they are only need­ed in extremely low amounts, most of them only a fraction of a pound per acre. Typically, we have optimum amounts of these nutrients to supply the crop’s needs. Also, diagnosing micronutrient deficiencies and prescribing applications are difficult because most agronomists have never seen these issues outside of a textbook. Ultimately, this complexity adds up to many misconceptions and seemingly contradicting claims related to micronutrients.

Of the 17 plant-essential nutrients, eight are classified as micronutri­ents: boron, chloride, copper, iron, manganese, molybdenum, zinc and nickel. They are considered micro­nutrients because they are found in extremely small amounts in plants. A macronutrient such as potassium may make up 1% of the plant’s dry weight, but a micronutrient such as boron will only make up 0.002%.

These nutrients are critical for sev­eral functions in the plant. Typically they are used as catalysts for other reactions or as minor ingredients of critical plant components like cell walls. We don’t have room to go into details for each micronutrient, so if you are interested in learning more, check out this publication from the University of Missouri’s Master Gardener series, found at bit.ly/MG_micronutrients.

When managing micronutrients, the first thing to understand is that they are seldom in low supply in the soil. Zinc is the only micronutrient that we commonly use a soil test to diagnose deficiencies in MFA’s trade territory. Adequate levels of other micronutrients are typically found in our soil profile.

However, sometimes deficiencies can arise and cause yield loss even when we have “good” soil test levels. That’s because the growing envi­ronment is more important than a soil test in many cases. Soil pH, organic matter levels and heavy clay or sandy soils (as indicated by cation exchange capacity) tend to be a bet­ter indicator of micronutrient needs than soil test levels.

Proper soil pH is something you can control, so lime applications— preferably variable-rate—can help with some micronutrient needs. Soil texture and organic matter are different. These are soil properties we can’t easily adjust, if at all. Sandy soils, for example, are most likely to exhibit micronutrient deficiencies. Just as we should spoon-feed nitro­gen and potassium on these soils, we may need to look at supplementing some micronutrients as well.

I also want to address growers who are trying to break yield barriers. Often, these producers are using many micronutrient packages, sometimes multiple times in a sea­son. While there is nothing wrong with this approach, it is typically unnecessary for our production fields. Taking advantage of these micronutrient applications requires an extreme understanding of the soils in each field and dedication to analyzing the crop in season. I appreciate what these producers do, but, in many cases, the solutions are tailored specifically to their local conditions. Use caution when apply­ing recommendations not made for your cropping environment.

As you likely realize by now, there is no simple, one-size-fits-all approach to micronutrient man­agement. If anyone tries to market micronutrients as a stand-alone solution, you should proceed with caution. Where does that leave us? In short, be diligent about checking your crop for issues, especially in more challenging soils, like heavy clays or sands. A good agronomist can be invaluable here. MFA Crop- Trak consultants, for example, see a wide variety of local soils and crops and can help you find solutions to address problems quickly.

If I had to make a broad gener­alization about what micronutrient fertilizers to use in our area, I would say zinc and boron—zinc because we often see low levels and boron because of its mobility in the soil. Situations may call for other micro­nutrients, but responses to these nu­trients can be few and far between.

My best advice is to focus on the basics, then keep your eyes open and don’t be afraid to ask questions if you see something unusual. Be sure to take care of any other fertility issues before chasing micronutrients. Soil pH, nitrogen, phosphorus, po­tassium and sulfur are critical to op­timum yields and must be addressed to gain any value from a micronutri­ent application. Micronutrients can play a part in achieving higher yields, but you must pay attention the en­tire system, not just one component, to be successful.

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