Plant Nutrition in Plant Science: Nutrients, Sources, and Fertility Decisions

Essential nutrients

Elements a plant must have to complete its life cycle; growth is limited if any nutrient is missing.

Liebig’s Law of the Minimum

Yield is controlled by the most limiting nutrient, similar to the shortest stave in a barrel.

Macronutrients

Nutrients needed in relatively large amounts, including primary and secondary macronutrients.

Primary macronutrients

Nitrogen (N), phosphorus (P), potassium (K).

Secondary macronutrients

Calcium (Ca), magnesium (Mg), sulfur (S).

Micronutrients

Nutrients needed in small amounts but are still essential, like iron (Fe), manganese (Mn), and zinc (Zn).

Chlorophyll formation

Process that requires iron (Fe) as a critical micronutrient.

Uptake forms of nitrogen

N absorbed mainly as nitrate (NO₃⁻) and ammonium (NH₄⁺).

Mass flow

Movement of nutrients carried with water pulled in by the plant.

Diffusion

Movement of nutrients from areas of high concentration to low concentration near roots.

Cation exchange capacity (CEC)

The ability of soil particles to hold positively charged ions (cations) like K⁺ and Ca²⁺.

Leaching

Loss of nutrients like nitrate (NO₃⁻) that moves below roots with water.

Mineralization

The process of soil microbes converting organic nutrients into plant-available inorganic forms.

Immobilization

Process where microbes take up inorganic nutrients, reducing availability to plants.

Soil pH

Affects nutrient solubility and chemical reactions; can decrease availability of micronutrients.

Phosphorus binding in soils

Phosphorus can bind with Fe and Al in acidic soils and with Ca in alkaline soils.

Organic nutrient sources

Nutrient sources derived from living or once-living materials, such as manure and compost.

Animal manures

Often provide nitrogen, phosphorus, potassium, and micronutrients; contributes organic matter.

N–P–K grade

Label indicating the percent by mass of nitrogen (N), phosphorus (P₂O₅), and potassium (K₂O) in fertilizers.

Chelated micronutrients

Micronutrient compounds that remain soluble and available in soils with challenging pH levels.

Sandy soils

Typically have low cation exchange capacity (CEC) and are prone to nutrient leaching.

Fertilizer application timing

Important for matching crop nutrient demand and minimizing environmental losses.

Organic sources strengths

Improve soil structure, offer slow-release nutrients, and recycle nutrients.

Inorganic sources strengths

Rapid nutrient availability, precise nutrient budgeting, and high nutrient density.

Nitrate vs. ammonium leaching

Nitrate (NO₃⁻) is more leachable than ammonium (NH₄⁺) due to its negative charge.

Split applications of N

A strategy to reduce nutrient leaching risk by applying close to peak crop uptake.

Soil testing

Essential for assessing nutrient availability and diagnosing potential deficiencies.