Electrical Conductivity (EC)

Electrical Conductivity (EC) is the measure of a solution's or soil's capacity to conduct electric current, expressed in deciSiemens per metre (dS/m, equivalent to mmhos/cm). It serves as a proxy for total dissolved salt concentration — every 1 dS/m corresponds to roughly 640 mg/L of dissolved salts. EC is measured with a calibrated probe in a 1:2 or 1:5 soil-water suspension for soil samples, or directly in liquid digestate, irrigation water, and fertigation tank-mixes. Routine measurement takes under 60 seconds at a cost of ₹50–150 per sample at accredited Indian labs.

EC values map directly onto crop tolerance categories. Soil saturation paste EC below 2 dS/m supports all common Indian crops; 2–4 dS/m affects sensitive crops like beans, onions, and citrus with 10–25% yield loss; 4–8 dS/m restricts cultivation to moderately tolerant crops like wheat, sorghum, and pomegranate; above 8 dS/m only salt-tolerant species (barley, date palm, cotton in selected varieties) perform. Irrigation water EC above 0.7 dS/m raises long-term soil salinity risk; above 3 dS/m it is generally considered unsuitable for sustained use without leaching fractions and gypsum applications.

For biogas digestate, raw EC is typically 5–15 dS/m — driven by ammoniacal nitrogen, potassium, sodium, and bicarbonate alkalinity from anaerobic fermentation. This is far above the EC tolerance of most crops if applied undiluted, which is why dilution at 1:5 or higher is required for fertigation. EC also matters during reactor operation: digester liquid above 25–30 dS/m inhibits methanogenesis through osmotic stress on the microbial community, signalling either ammonia accumulation or excessive sodium ingress (often from cleaning chemicals or salty industrial feedstocks). Indian CBG plants now routinely include inline EC sensors in digestate storage tanks as an early-warning indicator of process upset and product quality.

• Measure of dissolved salt concentration; 1 dS/m ≈ 640 mg/L total dissolved salts.
• Soil EC tolerance: under 2 dS/m universal, 4–8 dS/m for tolerant crops, above 8 dS/m for halophytes only.
• Raw digestate EC 5–15 dS/m requires 1:5+ dilution for fertigation.
• Digester EC above 25–30 dS/m signals process upset and inhibits methanogenesis.