SWAT Literature Database for Peer-Reviewed Journal Articles

Title:Validating soil phosphorus routines in the SWAT model 
Authors:Vadas, P.A. and M.J. White 
Journal:Transactions of the ASABE 
Article ID: 
URL (non-DOI journals):http://ddr.nal.usda.gov/handle/10113/46706 
Broad Application Category:pollutant only 
Primary Application Category:nutrient cycling/loss and transport 
Secondary Application Category:none 
Watershed Description:field study data from approximately 40 studies in multiple countries 
Calibration Summary: 
Validation Summary: 
General Comments: 
Abstract:Phosphorus transfer from agricultural soils to surface waters is an important environmental issue. Commonly used models like SWAT have not always been updated to reflect current understanding of soil P transformations and transfer to runoff. The objective of this study was to validate the ability of routines in both SWAT2000 and SWAT2005 to initialize the quantity of P in different soil P pools (and thus soil total P) and simulate changes in the simulated solution P pool. Based on data from 40 published studies, results show that currently published equations to estimate the soil PSP parameter and SWAT's method of summing four soil P pools underpredict soil total P. An underprediction of soil total could result in underprediction of P loss in runoff with eroded sediment. Conversely, the proposed alternative for estimating soil total P, which includes a new equation to estimate the soil PSP parameter and includes the solution P pool when summing soil P pools, resulted in accurate predictions of soil total P for 484 topsoil samples from 35 published studies. Results also show that both the SWAT routines and the routines proposed by a previous study for simulating changes in soil P were able to accurately predict longā€term changes in soil solution P. However, routines in both SWAT2000 and SWAT2005 may underpredict solution P for several weeks after P is added to soils. This could result in underprediction of dissolved inorganic P loss in runoff soon after a P application to soils. The routines proposed by the previous study would not result in similar underpredictions. 
Keywords:Modeling, Phosphorus, Soil, SWAT