Electrical Conductivity (1.0 – 10.0 dS/m) (EC 1.0–10.0 dS/m)

Electrical Conductivity (EC) of 1.0–10.0 dS/m describes the typical range of dissolved salt concentration in biogas digestate — measured by passing a current through a sample and reporting the conductance in deciSiemens per metre. The range is wide because digestate composition varies dramatically with feedstock: cattle-dung digestate sits at the lower end (1.5–3.5 dS/m), food-waste digestate is intermediate (3–6 dS/m), and digestate from saline or high-protein feedstocks can reach the upper end (7–10 dS/m).

EC matters because it directly relates to crop tolerance for digestate as a fertiliser. The total dissolved salts indicated by EC include nutrients (ammonium, potassium, calcium, magnesium) and non-nutrient salts (sodium, chloride, sulfate). Crops have specific EC tolerance thresholds: highly sensitive crops (strawberry, lettuce, citrus) tolerate up to 1.5 dS/m in irrigation water; moderately sensitive crops (rice, wheat, maize) tolerate 2–4 dS/m; tolerant crops (cotton, barley, date palm) tolerate 5–8 dS/m. Beyond crop threshold, dissolved salts impose osmotic stress on roots, blocking water uptake and causing leaf-tip burn, growth reduction, and yield loss — sometimes called nutrient burn.

For practical application, EC drives both rate and dilution decisions. Digestate at 3 dS/m can be field-applied at 10–20 m³/hectare per season without causing salinity build-up; digestate at 8 dS/m requires either dilution before fertigation, lower application rate, or restriction to salt-tolerant crops. Long-term application also matters — repeated digestate use on the same plot can raise soil EC over time, especially in low-rainfall areas where leaching is limited. The Soil Health Card scheme uses soil EC above 4 dS/m as the threshold for declaring saline soil, beyond which yield falls 25–50% for most major crops. Plants targeting horticulture and high-value vegetable markets typically pre-test EC every batch and blend or dilute as needed to maintain consistent product specification. Within the FCO 1985 framework for Liquid Fermented Organic Manure, EC is not yet a formal specification limit, but most farmer-facing brands now publish it on the label as a quality assurance indicator. The trade-off is straightforward: higher feedstock energy density (food waste, high-protein materials) yields more biogas but also higher digestate EC, narrowing the suitable end-use markets.