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Validating and Applying the Enhanced Dynamic Fertilizer Model (SWAT-DFC)

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Watershed ManWatershed Management to Meet Water Quality Standards and TMDLS (Total Maximum Daily Load) Proceedings of the 10-14 March 2007, San Antonio, Texas  701P0207.(doi:10.13031/2013.22429)
Authors:   James B Houser, Ali Saleh, Larry M Hauck
Keywords:   SWAT, watershed models, manure management, BMP, soil test phosphorus

While all of agriculture is affected by evolving environmental regulation, animal feeding operations, in particular, have come under close scrutiny, especially in the area of waste handling. In the area of manure handling, the most common best management practice (BMP) is to prescribe manure application rates based on the soil test phosphorus (STP) concentration. A dynamic fertilizer management component was added to the SWAT model (SWAT-DFC) that permits changing manure application rates and area based on STP values, and moves manure from one subbasin to another to find land available for manure application. SWAT-DFC was validated for the upper North Bosque River watershed in central Texas. The model simulated streamflow, sediment and nutrient loadings at the watershed outlet reasonably well, with goodness-of-fit (E) values greater than 0.70 for most simulated loads during the calibration period. SWAT-DFC was then used to assess a 30-year simulation scenario BMP based on the Texas Field Office Technical Guide (FOTG) Conservation Practice Standard 590 - Nutrient Management for Texas, compared to a 30-year baseline of manure applied at the nitrogen agronomic rate. The FOTG manure application strategy reduced final STP concentration on dairy waste application fields compared to the baseline scenario, with average and median concentrations of 50-55 ppm and 300 ppm respectively. However, the FOTG scenario required four times as much land as the baseline scenario. Ultimately, output from SWAT-DFC during the FOTG simulation confirmed that the manure transfer component of the model was working and gave a realistic accounting of potential manure transfers.

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