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United States Department of Agriculture

Agricultural Research Service

Research Project: ASSESSING MANAGEMENT EFFECTS ON CROPS AND SOILS Title: Re-defining and quantifying inorganic phosphate pools in the Soil and Water Assessment Tool

Authors
item Haney, Richard
item White, Michael
item Arnold, Jeffrey
item Haney, Elizabeth -
item Harmel, Daren

Submitted to: Journal of Soil Science and Environmental Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 19, 2013
Publication Date: December 31, 2013
Citation: Haney, R.L., White, M.J., Arnold, J.G., Haney, E.B., Harmel, R.D. 2013. Re-defining and quantifying inorganic phosphate pools in the Soil and Water Assessment Tool. Journal of Soil Science and Environmental Management. 4(8):155-162.

Interpretive Summary: The Soil and Water Assessment Tool (SWAT), a large-scale hydrologic model, can be used to estimate the impact of land management practices on phosphate (P) loading in streams and water bodies. The current version of the model relies on initial P concentrations based on soil type. This paper suggests the possibility of taking soil samples and analyzing them using specific soil extractants to define the pools prior to the model run. This way, the initial inputs will reflect a much better estimate of the P pools and should increase the accuracy of the predictive capabilities of the model.

Technical Abstract: Abstract The Soil and Water Assessment Tool (SWAT), a large-scale hydrologic model, can be used to estimate the impact of land management practices on phosphate (P) loading in streams and water bodies. Three inorganic soil P pools (labile, active, and stable P) are currently defined in the SWAT model. The labile (or soluble) inorganic P values may be user input, while the other pools are automatically defined by the model. This paper identifies methods readily available for use by laboratories so that the SWAT user may input the initial total, active and soluble P pool levels in mineral soils. Allowing the user to set the initial P values will inevitably increase the accuracy of the model. The authors found that water-extractable, Mehlich 3 and H3A were the most suitable soil extractants available to determine the soil extractable P pools based on their inherent properties and their relationships to each other. Based on these data, newly defined pools in SWAT would include the soluble pool as water extractable P (runoff potential) and the labile pool as defined by H3A (plant available). The active pool would be defined by Mehlich 3 extraction (recharging the depletion of the plant available pool and estimating a percentage of sediment bound P) and total P minus Mehlich 3 would comprise the stable pool. The redefining of soil P pools by soil extractant could enhance the accuracy of the SWAT P routines and allow the user to input data from their geographic area as improved initial values for soil P pools.

Last Modified: 12/25/2014
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