Calcium Nitrate — Frequently Asked Questions

Because the problem is usually transport, not supply. Most soils contain ample calcium, but it is present as barely soluble carbonate or sulphate, and calcium moves through the plant only in the transpiration stream. Leaves transpire heavily and receive plenty; fruit transpires little and can be starved even in calcium-rich soil. A soluble source applied through irrigation or as a foliar spray addresses the delivery problem directly.

Solubility and uptake. Calcium sulphate is only sparingly soluble, so it cannot be delivered through fertigation at useful concentration. Calcium nitrate is freely soluble, and nitrate uptake at the root actively promotes cation uptake alongside it, whereas an ammonium-based nitrogen source competes with calcium for the same uptake pathway.

To prevent hydrogen sulphide formation. In an anaerobic sewer or tank, bacteria reduce sulphate to hydrogen sulphide, producing odour and corroding concrete and metalwork. Dosing nitrate gives those bacteria a more favourable electron acceptor, so they use nitrate instead of sulphate and sulphide generation stops.

Sealed and dry. It is strongly hygroscopic and will absorb atmospheric moisture, caking and eventually deliquescing if left exposed. It is also an oxidiser and should be kept away from combustible material, fuels and heat, and stored separately from incompatible chemicals.