Definition

Phosphate (P) uptake by plants depends on the concentration of P in the soil solution, often referred to as plant-available P. This fraction represents the amount of phosphate that crops can directly absorb during the growing season.

Importance

Phosphate is an essential nutrient for plant growth, influencing root development, energy transfer, and overall crop productivity. However, its availability in soil is typically very low, making accurate assessment critical for effective fertilisation strategies.

 Buffering mechanisms

Although the concentration of plant-available P in the soil solution is small, it is buffered by various P fractions in the solid phase. These fractions interact through complex processes such as:

• Desorption–Adsorption
• Dissolution–Precipitation
• Mineralisation–Immobilisation

These processes maintain equilibrium between soil solution and solid-phase P.

 Influencing factors

The dynamics of P availability are strongly affected by:

• Root activity (uptake and exudates)
• Environmental conditions (temperature, moisture, pH).

Typical levels

Plant-available P is usually only a few kilograms per hectare, generally ranging from <2 to 20 kg P/ha. This represents the amount directly accessible to crops within the current season.

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