Macro and Micro: What You Need to Know About Soil Nutrients

:: Monday, May 15, 2017 :: Posted By Fabiano Silvestrin
Have you ever had a potted plant that—when you first got it—was the epitome of vibrancy and health? We all have. You may have done your part and watered it regularly: Not too much, not too little. For some time, it looked healthy and beautiful. But after a while, it began to wither, and eventually it died. Why? One word: Soil.
Think of soil like your refrigerator: You need to stock it with essential items to keep you healthy and moving. Additionally, you need to restock your fridge regularly.

Micronutrients: The right building blocks for optimal health

Like humans, plants have basic needs that need to be met. Plants require a steady supply of macronutrients and micronutrients. The difference between the two is quite simple: Macronutrients are required in larger quantities than micronutrients.
The names of the two categories don’t imply that one type of nutrient is more important than another; it just means that more macronutrients must be present in the soil than micronutrients. Plants obtain nearly all of the nutrients they need from the soil, although some are obtained via photosynthesis.
Macronutrients are divided into two groups: primary and secondary. The primary macronutrients are those that are needed in the highest concentration: Nitrogen (N), phosphorus (P), and potassium (K). In fact, these three primary nutrients are needed in higher concentrations than the rest of the macronutrients combined.
Secondary macronutrients are also required for sustained plant health, but in lower quantities than the primary macronutrients. Calcium (Ca), magnesium (Mg), and sulfur (S) comprise the secondary macronutrients.
Micronutrients are also essential to plant development and growth but are needed only in trace amounts, compared to their macro-counterparts. The seven critical micronutrients are:
  • Boron (B)
  • Zinc (Zn)
  • Iron (Fe)
  • Manganese (Mn)
  • Copper (Cu)
  • Molybdenum (Mo)
  • Chlorine (Cl)

The Law of Minimum

The importance of micronutrients can best be explained by analogy. Consider a barrel like the ones pictured here:

In a barrel, every plank (or “stave”) is 100% necessary and needed to retain the contents of the barrel. Like each stave of a barrel, every micronutrient is 100% necessary for healthy plant growth.
However, notice that in the left barrel, the stave labeled “boron” is shorter than the rest. A real barrel can only be filled up to the top of the shortest stave before its contents begin spilling out. The same can be said for plants; the least-available nutrient (ie, shortest “stave”) determines how well a plant can absorb and use all other nutrients. The plant is unable to use any nutrient that is added above that minimum level, so any extra nutrients are wasted. That minimum limits how well the plant grows and develops, ultimately impacting overall crop yield. This is known as the Law of Minimum.

Restocking with the healthy option

As you can see, plants require a steady supply of both macro- and micronutrients to stay healthy and produce optimal output. A lack of any one of these nutrients can significantly impact the health and longevity of a plant. Natural deficiencies in soil can be supplemented by using the proper applications and techniques to ensure proper development.
However, just as you should aim to stock your refrigerator with heathy foods, you should also replenish your soil with high quality products. Our image illustrates how the availability of boron affects crop yield and plant development.
In the barrel on the left, the soil is given an unrefined mineral borate fertilizer, which is not optimally water soluble. That means that the plants in this soil will not get as much boron as they need to be healthy and viable. The barrel on the right illustrates plant viability when refined borate fertilizer is applied to the soil. The high water solubility of the refined product means that more boron can be available to the plant during the course of the growing cycle, ensuring proper development and yield.
Like people, when plants get good nutrition, they can be at their best—and give farmers the best possible yield in return.



 boron basics soil science

U.S. Borax, part of Rio Tinto, is a global leader in the supply and science of borates—naturally-occurring minerals containing boron and other elements. We are 1,000 people serving 650 customers with more than 1,800 delivery locations globally. We supply around 30% of the world’s need for refined borates from our world-class mine in Boron, California, about 100 miles northeast of Los Angeles. Learn more about Rio Tinto.

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