Submitted to: United States Department of Agriculture Natural Resources Conservation Service
Publication Type: Government publication
Publication Acceptance Date: 6/15/2009
Publication Date: 6/15/2009
Citation: Plotkin, S., Potter, T.L., Bosch, D.D., Bagdon, J.K., Hesketh, E.S. 2009. I_APEX Calibration and Validation Using Research Plots in Tifton, Georgia. United States Department of Agriculture Natural Resources Conservation Service. http://www.nrcs.usda.gov/in ternet/FSEJ_documents/nrcs143_013180.pdf.2009. Interpretive Summary: Simulation models are valuable tools used to assess management practices, cropping systems, and other land use across a broad range of agricultural landscapes. Models continue to evolve providing more efficient computation and extending the scale to which they can be applied. Recently USDA-ARS scientists developed and refined a model, I_APEX, which allows evaluation of management practices at farm, field, and watershed scales. In this study, USDA-ARS Southeast Watershed Research Laboratory and USDA-NRCS scientists worked collaboratively to calibrate and validate I_APEX to describe the potential for pesticide runoff in the Southern Atlantic Coastal region of the USA. Calibration data were complied by the ARS group during studies of soil and water quality responses to conservation-tillage during rotational cotton and peanut production. Once calibration was complete the model was found to effectively describe both water and herbicide losses. The study has enhanced the value of I_APEX by showing that the model can effectively describe these landscape scale processes. This will improve confidence in the model results. Currently the model is being used at the national in the USDA Conservation Effects Assessment Program (CEAP).
Technical Abstract: The Agricultural Policy Environmental EXtender (I_APEX) simulation model was developed and is supported by the USDA-ARS Blacklands Research and Extension Center in Temple, Texas. I_APEX, which uses APEX as its core model, is an extension of the continually evolving Environmental Policy Integrated Climate (EPIC) model that was also developed by this research group. EPIC allows modeling of one field per simulation whereas I_APEX can perform simulations on contiguous fields and small watersheds. Like EPIC I_APEX is capable of simulating a wide array of management practices, cropping systems, and other land use. Advantage’s that I_APEX provided include the ability to make assessments across a broad range of agricultural landscapes including whole farms and small watersheds. Currently the model is being used to assess agricultural practices including pesticide use in the Conservation Effects Assessment Project (CEAP). CEAP began in 2003 as a multi-agency endeavor to quantify environmental benefits of conservation practices used by farmers participating in selected United States Department of Agriculture (USDA) Conservation Programs. Generally simulation models are used most effectively when calibrated and validated with field scale measurements. This report describes use of data developed by the USDA-ARS Southeast Watershed laboratory for calibration and validation of I_APEX. Data included a combination of detailed climatic and hydrologic measurements and loss of two herbicides from six 0.15-ha research plots over a period of two years. The plots which are located in South Central Georgia are representative of agricultural landscapes throughout much of the Southeastern USA. Overall, the calibration and validation showed that I_APEX provided estimates of water and herbicide losses that were in relatively close agreement with measured data.