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How to Make Foliar Fertilizer Decisions

07/07/2020
  • Mineral soils of the Midwest are well equipped to supply most micronutrient needs for high yielding corn and soybeans.
  • Soil testing and plant tissue sampling along with root examination and the growing environment provide a better understanding of crop nutrient deficiencies and needs.
  • Understanding the underlying cause of the nutrient deficiency provides the best opportunity of finding a long-term solution.

With fungicide applications right around the corner, the topic of micronutrients often comes up.Most Midwest soils contain large quantities of micronutrients in mineral and organic matter forms. However, when a micronutrient deficiency is discovered through tissue and soil sampling or visually observed, foliar products can be an alternative source for these micronutrients. Table 1 illustrates that Midwest soils are well equipped in most cases to supply sufficient micronutrients to crops, even at today’s high yields.Understanding total crop needs versus the amount of micronutrients that can be delivered through foliar products, can help determine which product is best to use.

 

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The range of micronutrient supplying power of the top six inches of soil doesn’t tell the complete story.  True micronutrient deficiencies can be caused by several factors.  These factors may include too low soil pH, too much or too little soil moisture (nutrients need to be in solution to be taken up and oxygen needs to be present), root abnormalities due to pruning or compaction, soil or air temperature shifts and true soil deficiencies.  All these factors alone or in combination can lead to nutrient deficiency symptoms or a hidden deficiency that does not present visual symptoms.  Discovering the true cause can solve the problem long term.  Unfortunately, deficiency symptoms can be difficult to discern, as they can resemble one another or those caused by environmental factors. Tissue testing paired with soil samples taken from affected and unaffected areas of the field, will provide more reliable nutrient deficiency information. 

Foliar products currently on the market all share a common carrier, water, which holds the nutrients in solution.  A gallon of water can only hold so much dissolved nutrient whether it may be many micronutrients combined or a concentration of only a few (≤ 3 nutrients).  For this reason, products containing only a few nutrients have a higher analysis of such nutrients compared to products containing many individual nutrients.  Higher analysis fertilizers are more likely to result in a yield response because they deliver a higher dosage of nutrients to the growing crop. Nonetheless, with some of these foliar fertilizers, it is still difficult to supply total nutrient needs in a single application.  If we are dealing with true soil deficiencies, correction is achieved more efficiently and economically with dry fertilizer products that have a higher nutrient analysis or by multiple applications of foliar products followed by dry fertilizer products of higher nutrient analysis.

Proper diagnosis involves obtaining a representative sample. When sampling a field, a sample area should not exceed 20 acres in size.  Always treat different hybrids or varieties as separate samples.  Initially break sample areas by soil type.  Next decide if elevation variances are great enough to create differences in soil mobile nutrient levels within the field.  Break high areas, side-hills and low areas of the field into separate sampled areas.  Be sure to take the proper plant part(s) and plant part number as indicated by the laboratory to which samples will be shipped to.  If necessary, wipe the dust and dirt from the plant parts with a damp paper towel so they are clean when shipped.  Even small amounts of soil can contain large quantities of nutrients than the plant tissue itself, skewing the test results.  At each location at which a tissue sample is collected, take a soil core next to the plant sampled and composite with cores collected next to plants from which representative tissue was collected from.  Ship to the lab in a manner that will ensure that the sample can still breathe and won’t decompose prior to analysis.  No plastic barriers should be created as they will not allow moisture to dissipate.   Avoid shipment over weekends and around holidays. 

In summary, when applying foliar products, focus product choice on those containing fewer nutrients and higher analysis to better satisfy crop needs.  If not treating for an identified nutrient deficiency, but simply to enhance yields, choose products containing minerals that are not found in Midwest soils, or those found in low amounts. For example, boron containing minerals are scarce in the Midwest and for corn, boron is important for seed/grain formation. For soybeans a good example is molybdenum, which is essential for nodule formation yet found in low amounts in Midwest soils. While understanding the many different foliar products available can be confusing, your FS Crop Specialist is trained in soil and tissue sampling and can help growers attain the biggest yield impact per acre. 


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