Validation of EPIC for Two Watersheds in Southwest Iowa

Abstract

The Erosion Productivity Impact Calculator (EPIC) model is validated using long-term data collected for two southwest Iowa watersheds that have been cropped in continuous corn under two different tillage systems. The annual hydrologic balance was calibrated during 1988-94 by adjusting the runoff curve numbers and residue effects on soil evaporation. Model validation was performed for 1976-87 using both summary statistics and parametric and nonparametric statistical tests. Overall, results show that EPIC was able to replicate the long-term relative differences between the two tillage systems. ABSTRACT<p>The Erosion Productivity Impact Calculator (EPIC) model was validated using long-

Evaluation of Epic for Assessing Crop Yield, Runoff, Sediment and Nutrient Losses From Watersheds With Poultry Litter Fertilization

“…Sediments, nutrients, pesticides, and animal wastes are the primary NPS pollutants from agricultural activities. Agricultural decision makers are encountering increasingly complex challenges, which require consideration of management and policy alternatives based on potential economic and environmental impacts (Chung et al, 1999). As a result of the shift to fewer and larger confined animal op- Temple,TX 76502; erations, environmental and economic issues associated with utilization or disposal of animal manures and litters has become a focal point of conservation efforts (Ribaudo et al, 2003;USDA and USEPA, 1999).…”

Historical Development and Applications of the EPIC and APEX models

“…Relatively strong agreement was found by Pierson et al (2001) between EPIC-predicted and measured phosphorus (P) losses in runoff, but predictions for single events were not as accurate. Long-term trends were accurately predicted by EPIC for conditions at Treynor, Iowa (Chung et al, 1999), although predicted annual losses were not as accurate. EPIC output did not compare well with measured in-stream loads for two large Lake Erie subwatersheds (Forster et al 2000), but relative results were correctly predicted except for soluble P.…”

“…Generally accurate predictions of leached N below the root zone or in tile flow, as compared with or implied by measured data, were found by Engelke and Fabrewitz (1991), Jackson et al (1994), Richter and Benbi (1996), Cavero et al (1997), Flowers, Easterling, and Hauck (1998), Cavero et al (1999), and Chung et al (2002). Somewhat weaker leached N or tile flow N loss predictions were found by Chung et al (1999) and Chung et al (2001), although both studies showed that EPIC was sensitive to long-term cropping and tillage Sediment; organic N and P; N and P in runoff; Total N and P in runoff and sediment; N in tile flow; sorghum-cotton rotation; 12 ha plots; 1 year Flowers, Easterline, and Hauck (1998) impacts on N losses. A sensitivity analysis by Benson et al (1992) showed that EPIC N leaching estimates can be very sensitive to choice of evapotranspiration routine and soil moisture estimates.…”

“…(Touré, Major, and Lindwall 1994), Swift Current, Saskatchewan (Kiniry et al 1995), and Swift Current, Saskatchewan (Roloff et al 1998), respectively; and (3) predicted corn yields in continuous corn grown during the 1976-87 period at Treynor, Iowa (Chung et al 1999). Bernardos et al (2001) found that long-term yield trends predicted by EPIC over several decades for the Argentine Pampa region were more accurate than the estimated yield variation, based on comparisons with historical yield data for corn, wheat, and sunflower.…”

“…Purveen et al (1997) reported that the EPIC MUSS option satisfactorily replicated snowmelt-induced runoff and erosion measured on plots near La Grace, Alberta. Median erosion rates of 58.8 and 3.6 t/ha were estimated with the EPIC USLE option by Chung et al (1999) for two watersheds in southwest Iowa that were cropped in continuous corn during the years 1976-87…”