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Soil Types And Drainage, Eric Bettenay, N. J. Schofield

Journal of the Department of Agriculture, Western Australia, Series 4

At least 90 per cent of the phosphorus entering the Peel-Harvey estuarine system comes from land cleared for agriculture, most of it from the coastal plain. These soils are naturally deficient on phosphorus and sulfur and this is supplied in superphosphate, which contains about 10 per cent phosphorus and 1 percent sulphur.

However, rain leaches some of this applied phosphorus from the land into drains and rivers which flow into the estuary. In 1981, farmers in the Harvey River-Mayfields Drain catchment lost the equivalent of 1,300 tonnes of superphosphate into the estuary. Between them they have in effect spent $120,000 …