As seen in Illinois AgriNews - http://www.agrinews-pubs.com/Content/News/Rural-Voices/Article/Check-soils-for-micronutrients-/8/15/15133
When accounting for the broad range of factors that can affect yield potential, it’s extremely important to evaluate the soil’s micronutrient profile—that mix of seven essential minerals growers can often overlook while making more conventional NPK fertility decisions.
Why Micronutrients Are Important
Crop production involves 16 basic elements, seven of which are micronutrients—boron, chlorine, copper, iron, manganese, molybdenum and zinc—that all serve specific functions ranging from plant hormone balance to photosynthesis.
Most soils are sufficient in these micronutrients, but others, such as more sandy or low organic-matter soils, can show a deficiency. Meanwhile, other fields can appear to have a deficiency if the soil pH is out of balance, affecting micronutrient availability.
Visible Micronutrient Deficiencies
Many distinct characteristics of micronutrient deficiencies may show in a plant’s physical appearance—most common is chlorosis, or yellowing of the leaves.
These deficiencies, however, will not be uniform throughout the field, as they may only occur in certain patches due to variations in soil profiles or properties, drainage, soil salinity and other aspects that can affect availability.
When scouting, growers should look for deficiencies in:
- Boron: a light chlorotic (yellow) appearance.
- Chlorine: wilting of younger leaves—rarely seen on crop plants in a field.
- Copper: a light chlorotic appearance, leaf-tip dieback or leaves twisted due to loss of turgor pressure.
- Iron: chlorosis between the veins of new leaves.
- Manganese: very similar to the appearance of an iron deficiency.
- Molybdenum: chlorosis of young plant material and the oldest plant material.
- Zinc: stunted growth, reduced internode length—young leaves are much smaller than others in the plant.
If any of these signs raise a red flag, gather a grown-plant tissue sample and send it to a trusted, qualified lab for an accurate analysis, as the current herbicide program or the presence of a disease may be the problem instead.
If it is, in fact, a micronutrient issue, the best method for replenishing these micronutrients back into the plant is to apply a starter fertilizer to the soil or through a foliar feeding by broadcasting the fertilizer over the top of the crop.
As Always, Soil pH Is Critical
Again, soil pH has a role in the availability of micronutrients, much the same way it impacts the core elements of an NPK (nitrogen, phosphorus and potassium) program. If the pH is either too basic or acidic, it can affect the plant’s micronutrient uptake. The optimal pH is between 5.5 and 7.0, and regularly scheduled soil testing is always recommended.