Nutrient Cycling in Agroecosystems

, Volume 75, Issue 1–3, pp 233–246 | Cite as

Application of reactive phosphate rock and sulphur fertilisers to enhance the availability of soil phosphate in organic farming

Original paper


Plant available soil phosphate is frequently deficient for crop and pasture production on organic farms in southern Australia. Improved P management, including developing a fertiliser product conforming to organic farming regulations, is required to sustain and increase production on these farms. Reactive phosphate rock (RPR) and elemental sulphur (S) are natural products. Field and pot experiments were established to measure the impact of ground RPR, and co-treatment of RPR with finely ground S, on available soil phosphate (Olsen P), plant dry matter, and the P concentration (%) and content (kg P ha−1) of the dry matter. Under dry-land field conditions characteristic of cropping regions in southern Australia ( < 600 mm rainfall, organic carbon  < 3%), co-treatment of RPR with S was necessary to increase Olsen P, and higher values of Olsen P were generally associated with increased plant dry matter, together with P concentration or P content of the dry matter. The required amount of S was less the more acidic the soil, but greater than reported as being effective in situations of higher rainfall ( > 1,000 mm) and soil organic carbon concentration (OC 11%). It was deduced that the S is probably required to overcome the constraint on dissolution of RPR resulting from frequent periods of low soil moisture. It was concluded that for the south-eastern Australian cropping zone, co-treatment of ground reactive phosphate rock with finely ground elemental S, at ratios (RPR:S) of at least 2:1, depending on soil pH, is required for effective use␣of RPR, even in strongly acidic soil (pHCa < 4.5). It was recommended that ‘organic’ farmers may recover soil P fertility by applying RPR  + S fertiliser to the most acidic fields, postponing soil liming, and managing the fields to conserve soil moisture.


Organic farming Available P Rock phosphate Sulphur 


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The authors are grateful for the support and infrastructure of the NSW Department of Primary Industries and the financial assistance of the Rural Industries Research and Development Corporation. We also thank Fertico Pty Ltd for provision of the reactive phosphate rock and the farmers who provided land, machinery and labour in support of this project.


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Copyright information

© Springer Science+Business Media B.V. 2006

Authors and Affiliations

  1. 1.NSW Department of Primary IndustriesAgricultural InstituteWagga WaggaAustralia

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