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From the Fields

Q: Macronutrients vs micronutrients, what is the difference?

A: All essential nutrients have a critical concentration – the minimum concentration required for plant growth. These concentrations vary from plant species to species. However, we can categorize 14 of the essential nutrients into two categories based on the minimum concentrations needed by plants.

Macronutrients - nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur - are needed in the highest concentrations by plants. Micronutrients - chloride, iron, boron, manganese, zinc, copper, molybdenum and nickel - are required in lower amounts for plant growth. However, all macronutrients and micronutrients can result in yield reduction when they are available in limited supply (Liebig's Law of the Minimum).

Cristie Preston, PhD
Nutrien | Senior Agronomist

From the Fields

Q: Why are some nutrients mobile in soil, but not within the plant?

A: There is a common misconception that if a nutrient is mobile within the soil, it is also mobile or can be translocated within the plant. The mobility of a nutrient in the soil is associated with how much can be leached - nitrate or sulfate, for example - or move with water. A good example of a nutrient that is immobile in soil is phosphorus.

The mobility of a nutrient within the plant determines where nutrient deficiency symptoms show up. Mobile nutrients in plant tissue, like nitrogen, phosphorus, and potassium, can be translocated to newly developing leaves and growing portions of the plant and therefore, result in deficiency symptoms in the lower, older leaves. Immobile nutrients are unable to be translocated, so when nutrient supply is low, the new growth is where the deficiency symptoms occur.

Diagram

Generalized diagram showing the portion of the plant where nutrient deficiency symptoms are first observed. Adapted 4R Plant Nutrition Manual, IPNI 2012

Cristie Preston, PhD
Nutrien | Senior Agronomist