EC (Electrical Conductivity) and TDS (Total Dissolved Solids)

EC (Electrical Conductivity)

What EC is

EC measures the total concentration of dissolved salts (ions) in the root zone. It does not identify which ions are present—only the overall ionic strength.

Why EC matters

• Determines osmotic pressure
• Controls how easily roots can take up water
• High EC reduces water uptake even when nutrients are present

Low EC

• Underfeeding
• Slow growth
• Pale foliage

High EC

• Osmotic stress
• Leaf burn / tip scorch
• Reduced uptake of Ca and Mg
• Root damage under sustained excess

Important distinction

Two solutions with the same EC can behave very differently depending on ion balance (e.g., NaCl-heavy vs nutrient-balanced).

TDS (Total Dissolved Solids)

What TDS is

TDS is the total mass of dissolved substances in water, usually expressed as ppm (mg/L).

Relationship to EC

TDS is often estimated from EC using a conversion factor (commonly EC × 500–700). The correct factor depends on ion composition.

Limitations

TDS does not distinguish nutrients from harmful salts. For fertigation decisions, EC is usually more useful, supported by a water or solution analysis.