Application of reactive phosphate rock and sulphur fertilisers to enhance the availability of soil phosphate in organic farming
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.
KeywordsOrganic farming Available P Rock phosphate Sulphur
Unable to display preview. Download preview PDF.
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.
- Attoe OJ, Olson RA (1966) Factors affecting rate of oxidation of elemental sulphur in soils and that added␣in rock-phosphate-sulphur infusions. Soil Sci 101:317–324Google Scholar
- Evans J (2005) Soil phosphorus fertility for broad-acre organic cropping systems. Aust Org J 62:36–37Google Scholar
- Lee A, Watkinson JH, Nguyen ML (1992) Oxidation of elemental sulphur by Thiobacilli in soils from New Zealand. In: Hilal MH (ed) Proceedings of Middle East Sulphur Symposium, Cairo February 1990. National Research Centre, Sulphur Institute, Washington, DC, pp 109–124Google Scholar
- Lipman JG, McLean HC (1917) Vegetation experiments on the availability of treated phosphates. Soil Sci 4:337–342Google Scholar
- Lipman JG, McLean HC (1918) Experiments with sulfur-phosphate composts conducted under field conditions. Soil Sci 5:243–250Google Scholar
- MacKay AD, Syers JK, Gregg PEH, Tillman RW (1984) A comparison of 3 soil-testing procedures for estimating the plant availability of phosphorus in soils receiving either superphosphate or phosphate rock. N Z J Agric Res 27:231–245Google Scholar
- Moody PW, Bolland MDA (1999) ‘Phosphorus’. In: Peverill KI, Sparrow LA, Reuter DJ (eds) Soil analysis—an interpretation manual. CSIRO, Collingwood, pp 187–220Google Scholar
- Moore AW, Isbell RF, Northcote KH (1983) Classification of Australian soils. In: Soils: an Australian viewpoint. C.S.I.R.O, Melbourne/Academic Press, LondonGoogle Scholar
- Olsen SR, Cole CV, Watanabe FS, Dean LA (1954) Estimation of available phosphorus in soils by extraction with sodium bicarbonate. US Department of Agriculture, Circular No. 939Google Scholar
- Penfold C (2000) Phosphorus management in broad-acre organic farming systems. Commissioned review: Rural Industries Research and Development Corporation, Canberra, 44 ppGoogle Scholar
- Swaby RJ (1975) Biosuper—biological superphosphate. In: McLachlan KD (ed) Sulphur in Australasian agriculture. Sydney University Press, Sydney, pp 213–220Google Scholar
- Swaby RJ (1983) Production and uses of biological superphosphate. In: Soils—an Australian viewpoint. CSIRO, Melbourne, pp 819–823Google Scholar