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

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).