Pasture environments in Australia where reactive phosphate rock will be an effective phosphate fertiliser

Abstract

Summary. Maps are constructed using Geographic Information Systems (GIS) computer technology to identify privately held land in the high rainfall zones of temperate and tropical Australia where highly reactive phosphate rocks (RPRs) are likely to be effective phosphorus (P) fertilisers for permanent pasture. Australia-wide RPR suitability maps were based on annual rainfall, soil pH and the P sorption capacity of the soil. The digitised soil map from the Atlas of Australian Soils and the soil profile acidity map derived from the Atlas, were used to identify land areas with suitable soil properties. The coarse scale of the Atlas, which has only the 1 dominant soil for each 100 ha minimum landscape unit, limits the precision in identifying specific land types. Reactive phosphate rock suitability maps for pasture land in Victoria were also developed using smaller land units and state-wide digitised soil maps for surface pH and surface texture. The GIS maps indicated that there are about 26.5 × 10⁶ ha of land in the high rainfall pastoral zone of Australia that have sufficient annual rainfall and appropriate soil properties for RPR to become effective by the 4th year after changing from annual water-soluble P fertiliser to RPR fertiliser applications. Additional land with a lower rainfall might also be suitable if the soil surface is not excessively sandy. The area of high rainfall pasture land where RPR is likely to be as effective as water-soluble P fertiliser in the first year of application is around 3 × 10⁶ ha. The major portion of this land is in North Queensland, with smaller areas in southern Victoria, in far north-west Tasmania and in the far south-west of Western Australia. More detailed GIS maps for Victoria indicate that RPRs would become as effective as water-soluble P fertiliser by the 4th year on more than 70% of private land where annual rainfall exceeds 700 mm.