Don’t Forget Micros in Your Fall Fertilizer Blends

Posted on: Sep 11, 2017

As harvest progresses, many of you will be shifting focus to fall soil sampling and fall fertilizer applications. This is an excellent time to consider how frequently your in-season tissue samples returned micronutrient values that were less than optimum. While in-season foliar application of micronutrients can be profitable, it is important to remember these foliar applications are temporary corrections. Chronic micronutrient deficiencies require soil application as well. Fall broadcast fertilizer applications are an excellent time to include micronutrients in the blend to address these ongoing micronutrient deficiencies.

Here is a generalized interpretation of soil test results for micronutrients. Keep in mind that adequacy in the plant is governed by many factors including but not limited to:

  1. the soil test result
  2. competitive interactions with other nutrients
  3. soil pH
  4. organic matter content
  5. root health
  6. soil moisture
  7. crop condition

Recommendations will be provided by the laboratory performing the soil analysis. The lab’s soil test interpretation may be slightly different than those shown above, but they should be close. The lab’s recommendations are generally assumed to be broadcast applications of inorganic nutrient sources. If using impregnated and/or chelated micronutrient sources, some adjustment in application rates based on fertilizer efficiency may be warranted. However, sometimes we just need “pounds” of nutrient to facilitate the correction in the soil, and the most economical approach to do that is with inorganic nutrient sources.

Micronutrients play many vital roles in plant growth, and a summary of their more noteworthy functions are:

  • Boron (B) – 1)Essential in pollination and reproduction 2) Aids in translocation of sugars and carbohydrates 3) Essential for seed and cell wall formation
  • Copper (Cu) – 1)Functions as a catalyst in photosynthesis and respiration 2) Plays an indirect role in chlorophyll production 3) Important in carbohydrate and protein metabolism 4) Important to formation of lignin in cell walls 5) Affects the flavor, storageability and sugar content of fruits
  • Iron (Fe) – 1) Essential for chlorophyll development and function 2) Acts as an oxygen carrier and is a constituent of certain enzymes and proteins 3) Involved in reactions involving cell division and growth
  • Manganese (Mn) – 1) Functions as part of certain enzyme systems 2) Aids in synthesis of chlorophyll and in assimilation of nitrate 3) Increases availability of phosphorus and calcium 4) Functions in formation of riboflavin, ascorbic acid and carotene
  • Zinc (Zn) – 1)Essential for the production of auxins 2) Activates enzymes in protein synthesis 3) Necessary for chlorophyll formation 4) Influences rate of seed and stalk maturation 5) Presence of adequate zinc in plant tissues enables plant to withstand lower air temperatures

A few dollars invested in micronutrients now will pay dividends in the months to come.

- Michael Larkin, Agronomist