Reclamation of a calcareous saline‐sodic soil using phosphoric acid and by‐product gypsum

Abstract Phosphoric acid is increasingly used as a source of water‐soluble P, but it has not been widely tested for its effectiveness in reclaiming calcareous sodic and saline‐sodic soils relative to chemically equivalent rates of gypsum. In lysimeters experiments, we showed that a calcareous saline‐sodic soil can be ‘reclaimed’ using phosphoric acid and leaching with moderately saline irrigation water (sodium adsorption ratio = 4.1 and electrical conductivity = 2.2 dS/m). Phosphoric acid (50% pure) was dissolved directly in the leaching water at application rates of 450, 600 and 900 kg/ha, and phosphogypsum (80% pure) was mixed with soil prior to leaching at application rates of 15, 20, 30 and 40 t/ha. Phosphoric acid was more efficient than the chemical equivalent of phosphogypsum in improving soil hydraulic conductivity, and in reducing the exchangeable sodium percentage (ESP). The ESPs after leaching were: 10 (water only), 5.5–5.3 (phosphoric acid) and 8.2–5.9 (phosphogypsum).