The Finer Details of Micronutrient Availability
Even though nutrients are labeled as micronutrients, secondary nutrients, and macronutrients, they are all subcategories within the group of recognized essential elements for plant growth. Nitrogen, phosphorus, and potassium are not more essential than zinc, boron, manganese, iron, et cetera. They are all essential, just required in different amounts at different times.
When thought about in that way, it is hard to rationalize how the conventional approach to soil fertility treats micros and macros differently. Many farms test regularly and assume replacement levels of P and K need to be applied and worry about mining the soils if they don’t add P and K each year. Yet many of those same crop acres have probably never been tested for micronutrient levels and never had any specific micronutrient products supplied.
Ag Spectrum Research and Teaching Agronomist, Dr. Jim Smart, helps make sense of this by answering questions on what farmers should be thinking about when it comes to micronutrients.
Q: Why should farmers be concerned about micronutrient availability in their soil?
A: To maximize profit and economic crop yields, providing the optimum soil environment for crops to thrive is essential. Unlike macronutrients, micronutrients aren’t needed in hundreds of pounds per acre. For the most part, they’re needed in ounces per acre, but they’re still needed. Just because micronutrients are needed in much smaller amounts than macronutrients, does not mean they aren’t as important. Soils that are deficient in micronutrients are going to greatly affect the plant’s ability to set and hold fruit.
Most soils have not been tested for micronutrients, however, it’s not uncommon in fields that have very high testing levels of potash and DAP to have zinc deficiency show up in corn. Why? Well, sometimes soils have such high levels of macronutrients that it’s hard for the binding sites to take up the micronutrients that are also needed. This would be a case of the soil profile being overloaded with nutrients. Crops need the correct nutrients in the soil profile at the time need them and in a form that they can uptake.
Q: What factors limit micronutrient availability?
A: Excessive phosphorus ties micronutrients up in the soil, and pH is also important to be aware of because high pH makes it difficult for plants to uptake nutrients like iron and zinc. Low pH poses a problem for nutrients like calcium. Balancing soils and getting them to neutral pH is incredibly important. Calcium-based lime and sulfur products are beneficial in accomplishing this.
In situations with soil compaction or a warm, dry period, micronutrients can become less available for plant uptake because the microbes that release and cycle micronutrients are less active. Changing herbicide programs can also affect root growth and hinder the plant’s ability to take up micronutrients.
Q: How do farmers correctly diagnose and fix micronutrient deficiency?
A: Micronutrient deficiencies can be difficult to scout and recognize because the symptoms are often missed or misdiagnosed. Even when they are correctly identified, the issue is usually not one specific micronutrient. A package of several micronutrients is needed to overcome a deficiency and it needs to be a package of chelated micronutrients like in Ag Spectrum’s Kick-Off®.
Chelated nutrients don’t bind readily to other soil particles, so they’re more available for plant uptake. They’re not tied up by other things going on in the soil right away. The plant roots can take those up readily without the interference of other factors in the soil.
It is more economically efficient to apply a small amount of micronutrients at a particularly critical growth stage, in a way that gives every plant access to avoid any deficiencies, than it is to try to predict where a deficiency will occur in attempt to deal with that specific area only.
Banding the nutrition in the seed furrow at planting allows farmers to use small amounts at the beginning of the growing season, rather than broadcasting it on in a much larger volume later just to hope the plant might find them. If a farmer were to broadcast apply these nutrients, it would not be economical because they would use a much larger volume and hope that at some point the plant could find them and take them up. When banding it right under the seed, a chelated formulation can be accessed by the plant when it needs it.
Q: Besides at planting, what other time is important for micronutrient availability?
A: During the reproductive phase, a plant’s access to micronutrients determines their ability to set and hold fruiting structures. A foliar nutrient mix like Ag Spectrum’s Score® at pollination penetrates the leaf and stimulates root growth so the plant can take up more of the naturally occurring nutrients in the soil throughout pollination. Nutrition provided by Score can help the plant set and hold more fruiting structures as well as fill those structures so they can become harvestable grain or fruit.
Q: How can farmers properly time macro and micronutrients for plant uptake?
A: Crops need the correct nutrients in the soil profile at the time need them and in a form that they can uptake. For example, if a soil is low on boron and the farmer decides to add copious amounts of boron to the soil not paying attention to timing, those plants will not use that boron.
In another instance, if there is a plant uptake issue because of dry weather or soil compaction or herbicide problems, plants are not taking up the micronutrients that are most needed at that time for reproduction. Tests can be done, but there’s a lot of variability with micronutrients. Their uptake ability depends on things like temperature and moisture, and they depend upon microbial population to help release micronutrients and make them available in the soil solution so the plants can take them up.
If all these factors are not working together in a system, even soil that tests high in micronutrients can present deficiencies.