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

Area of Science:

• Environmental Science
• Agricultural Science
• Soil Science

Background:

• Agricultural phosphorus (P) transport in runoff poses environmental risks.
• Current models inadequately simulate P release and transport from surface-applied manures.

Purpose of the Study:

• To develop a computer model that accurately simulates P release and transport from surface-applied manures.
• To improve the assessment of P loss from manured soils at field and watershed scales.

Main Methods:

• A daily-basis model simulating manure application, P infiltration, and partitioning into four P pools (water-extractable inorganic/organic, stable inorganic/organic).
• Simulation of manure dry matter decomposition, stable P transformation, and soil assimilation via bioturbation.
• Modeling of P leaching by rain and subsequent transfer to surface runoff, with P retention in the top soil layer.

Main Results:

• The model accurately predicted cumulative P loads in runoff across multiple field studies.
• It successfully simulated the dynamics of manure dry matter, manure/soil P pools, and storm-event runoff P concentrations.
• Predicted runoff P concentrations were significantly correlated (r²=0.57) with measured concentrations, though slightly underestimated.

Conclusions:

• The developed model offers a significant improvement for assessing P loss from manured soils.
• It enhances the simulation capabilities of field and watershed-scale models for P transport.
• Accurate P transport modeling is crucial for mitigating environmental concerns associated with agricultural runoff.