Effect of sulphur, sulphuric acid and gypsum on the yield of rice on the Cununurra soils of the Ord Irrigation Area, Western Australia

Abstract

A field experiment was conducted at Kimberley Research Station near Kununurra, Western Australia, to compare elemental sulphur, sulphuric acid and gypsum as soil ameliorants for drill-sown rice on the Cununurra clay of the Ord Irrigation Area. The application of sulphur (0.5-4 t ha-1) and concentrated sulphuric acid (800-1 600 1 ha-1) to Cununurra clay temporarily decreased soil pH, improved seedling establishment and increased the mean grain yield of Bluebonnet 50 and IR661-1-170-1-3 rice from 4.27 to 5.32 t ha-1. Plant growth during the first 6 weeks was better and the transient iron chlorosis, which often develops after permanent flooding, was largely eliminated. Gypsum (1-4 t ha-1) had no significant effect on soil pH, seedling establishment, early growth or grain yield. Mean pH of the flooded soil (0-5 cm) one month after permanent flooding was 6.60, 6.56, 6.07 and 5.52 in the untreatad, gypsum, sulphur and sulphuric acid plots, respectively. Mean grain yield increased linearly as the pH of the flooded soil (0-5 cm) one month after permanent flooding decreased over the range of 6.5-5.5. The pH values of air dried soil samples takgn at 3, 6, 9 and 11 weeks after sowing and determined at the saturation moisture content fell by 0.5 to 2 units after the addition of sulphur and sulphuric acid. The decrease in pH at 3 weeks after the application of 800 l ha-1 sulphuric acid was five times greater than that due to an equivalent amount of elemsntal sulphur, but the effect of the acid was short-lived. Calcium and magnesium concentrations in the saturation extracts of the air-dried soil samples taken at 3 and 6 weeks after sowing were increased by the application of sulphur and gypsum. All ameliorants increased the nitrogen concentration in the plant tops at 3 weeks after sowing but only sulphur and sulphuric acid increased phosphorus, potassium, manganese, zinc or iron concentrations at one or more sampling dates.