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RESEARCH ARTICLE

A new model for dung decomposition and phosphorus transformations and loss in runoff

P. A. Vadas A E , S. R. Aarons B , D. M. Butler C and W. J. Dougherty D
+ Author Affiliations
- Author Affiliations

A USDA-ARS, U.S. Dairy Forage Research Center, 1925 Linden Drive West, Madison, WI 53706, USA.

B Ellinbank Research Institute, Department of Primary Industries, Hazeldean Rd, Ellinbank, Vic. 3821, Australia.

C 2431 Joe Johnson Dr., University of Tennessee, Knoxville, TN 37996-4561, USA.

D Department of Primary Industries, Industry and Investment New South Wales, Locked Bag 4, Richmond, NSW 2753, Australia.

E Corresponding author. Email: peter.vadas@ars.usda.gov

Soil Research 49(4) 367-375 https://doi.org/10.1071/SR10195
Submitted: 14 September 2010  Accepted: 19 November 2010   Published: 19 May 2011

Abstract

Non point-source pollution of fresh waters by agricultural phosphorus (P) can accelerate eutrophication of surface waters and limit their use for drinking, recreation, and industry. An important pathway of agricultural P transport is surface runoff, to which unincorporated dung from grazing cattle can be a significant contributor. Computer models commonly used to identify agricultural areas with a high potential for P export do not adequately simulate dung application to the soil surface, dung disappearance, and dung P loss to runoff. We developed a new model to simulate these processes for grazing cattle dung. The model simulates dung organic matter decomposition and assimilation into soil by bioturbation as a function of air temperature and dung moisture. We validated that the model can accurately predict rates of dung disappearance, using data from 12 published studies. The model also simulates four pools of inorganic and organic P, P mineralisation to water-extractable P, leaching of dung water-extractable P into soil by rain, and loss of dissolved inorganic P in runoff. We validated the ability of the model to reliably simulate these P processes, using data from six published dung P transformation studies and six runoff studies. Overall, the model represents a novel approach for assessing the environmental impact of grazing dairy and beef cattle. Research should investigate the impact of dung deposition rate as a function of time and animal diet and type, where deposition occurs relative to runoff movement, weather conditions, and the ability of dung pad crusting to reduce P release to runoff.

Additional keywords: dung, phosphorus, runoff, model.


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