Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/1/2004
Publication Date: 8/16/2004
Citation: Cox, J.W., Smith, D.R. 2004. Erosion and phosphorus mobility from agricultural catchments. In: (W.J. Chadron and G.F. Koopmans eds.) 4th International Phosphorus Workshop: Critical evaluation of options for reducing phosphorus loss from agriculture. Wageningen, The Netherlands. August 16-19, 2004. p. 13.
Technical Abstract: The full impact of diffuse sources of P from agricultural lands, particularly the movement of particulate P in surface runoff of eroded soil material, was discovered after point sources of P to streams were largely removed by legislation. Management aimed at minimizing erosion, to minimize P loss, was introduced (such as no till cropping), and buffer strips were planted. In some regions in Australia, this management was effective in reducing particulate P in runoff to streams whereas in others, stream P levels continued to increase. Dissolved P in runoff was consistently high throughout the year. In contrast, particulate P dominated flows at the start of the season when the loam over clay soils had minimal vegetation and were vulnerable to erosion. Increased rainfall intensity later in the growing season, when pastures were established, did not significantly increase particulate P. While conservation tillage practices can lead to increased soluble P losses, resulting from surface application of fertilizers, particulate P fractions represent 3 to 40 times more P than the soluble fractions from cropland. Particulate P dominates flow from the parts of the landscape where easily erodible sodic soils form. Sediment and P losses from seepage areas within the catchments have been found to be an order of magnitude higher compared to drainage conditions. Phosphorus in the particulate form can move through clay subsoil within macropores and the amount of P mobilized was controlled by the "residence time." P in drainage from wet soil cores was significantly less than P lost through dry soils. However, soils that are saturated for long periods of time tend to have more P loss potential than well-drained soils. Thus it was shown that to reduce P loss to groundwater, streams or surface water storages across the agricultural regions of southern Australia, management must not only concentrate on reducing erosion at the start of the growing season. Management must include stabilizing sodic soils and keep them from becoming saturated, and increase the residence time of P, thereby allowing mineral and organic fractions time to sorb P.