A model for phosphorus transformation and runoff loss for surface-applied manures

P. A. Vadas, W. J. Gburek, A. N. Sharpley, P. J.A. Kleinman, P. A. Moore, M. L. Cabrera, R. D. Harmel

Research output: Contribution to journalArticlepeer-review

101 Scopus citations


Agricultural P transport in runoff is an environmental concern. An important source of P runoff is surface-applied, unincorporated manures, but computer models used to assess P transport do not adequately simulate P release and transport from surface manures. We developed a model to address this limitation. The model operates on a daily basis and simulates manure application to the soil surface, letting 60% of manure P infiltrate into soil if manure slurry with less than 15% solids is applied. The model divides manure P into four pools, water-extractable inorganic and organic P, and stable inorganic and organic P. The model simulates manure dry matter decomposition, and manure stable P transformation to water-extractable P. Manure dry matter and P are assimilated into soil to simulate bioturbation. Water-extractable P is leached from manure when it rains, and a portion of leached P can be transferred to surface runoff. Eighty percent of manure P leached into soil by rain remains in the top 2 cm, while 20% leaches deeper. This 2-cm soil layer contributes P to runoff via desorption. We used data from field studies in Texas, Pennsylvania, Georgia, and Arkansas to build and validate the model. Validation results show the model accurately predicted cumulative P loads in runoff, reflecting successful simulation of the dynamics of manure dry matter, manure and soil P pools, and storm-event runoff P concentrations. Predicted runoff P concentrations were significantly related to (r2 = 0.57) but slightly less than measured concentrations. Our model thus represents an important modification for field or watershed scale models that assess P loss from manured soils.

Original languageEnglish (US)
Pages (from-to)324-332
Number of pages9
JournalJournal of Environmental Quality
Issue number1
StatePublished - Jan 2007

All Science Journal Classification (ASJC) codes

  • Environmental Engineering
  • Water Science and Technology
  • Waste Management and Disposal
  • Pollution
  • Management, Monitoring, Policy and Law


Dive into the research topics of 'A model for phosphorus transformation and runoff loss for surface-applied manures'. Together they form a unique fingerprint.

Cite this