Work out gypsum requirement instantly with clear inputs, formula shown and shareable results.
Reclaiming a sodic soil means replacing exchangeable sodium with calcium. The sodium to displace is CEC x (current ESP - target ESP)/100 in cmol/kg, and each cmol/kg needs 0.086 tonnes of pure gypsum per 100 tonnes of soil. Soil mass follows from the reclamation depth and a bulk density of 1.4 t/m3.
Gypsum requirement
Exchangeable Na to replace (cmol/kg) = CEC x (ESP_current - ESP_target)/100
Mass basis
Gypsum (t/ha) = 0.086 x cmol/kg x soil mass (t/ha) / 1000; soil mass = depth (m) x 10,000 x 1.4
Sodic soil reclamation requires adequate drainage; leaching displaced sodium without it can salinise adjacent land and shallow groundwater. Have a soil chemistry report interpreted by a specialist before large-scale application.
Only slightly. Gypsum swaps sodium for calcium and improves structure without acidifying. For a sodic soil that is also alkaline with free carbonate, elemental sulphur or acidified amendments are needed to move pH.
Yes. The displaced sodium must be flushed below the root zone with good-quality water and adequate drainage, otherwise it re-adsorbs and the reclamation fails.