AbstractAn ion selective electrode was used to measure the nitrate ion concentration in pastes of soil and saturated calcium sulphate solution. A good correlation, for both air‐dried and field‐moist soil samples, was obtained between nitrate values found by colorimetric analysis subsequent to KC1 extraction, and those found by a nitrate electrode, non‐porous reference electrode couple. A ceramic frit reference electrode, although effective in pastes of air‐dried soils, gave rise to erroneous results in pastes of field‐moist soils.