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Title: Evaluation of the Cropland Modeling Component of the U.S. National Scale CEAP Project: Estimation of Soil Hydraulic Properties

item Nemes, Attila
item Timlin, Dennis
item Quebedeaux, Bruno
item Reddy, Vangimalla

Submitted to: International Soil Conservation Organization Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 5/18/2008
Publication Date: 5/19/2008
Citation: Nemes, A., Timlin, D.J., Quebedeaux, B., Reddy, V.R. 2008. Evaluation of the Cropland Modeling Component of the U.S. National Scale CEAP Project. In: Proceedings of the 15th International Congress of the International Soil Conservation Organization (ISCO), May 18-23, 2008, Budapest, Hungary. 2008 CDROM.

Interpretive Summary:

Technical Abstract: The USDA-NRCS is partnering with other agencies to conduct a national assessment of environmental benefits and effects of 2002 Farm Bill programs. One of the components of the resulting Conservation Effects Assessment Project (CEAP) is a national-scale effort to estimate the environmental benefits of implementing conservation practices in the field. The Agricultural Policy Environmental Extender (APEX) model has been proposed for use to evaluate on-site benefits of conservation practices in place in cultivated croplands. Farmer surveys have been conducted at a subset of NRI sample points about ongoing farming activities and conservation practices; and an array of databases has been generated and utilized to provide base data to the simulation model. Existing data provides baseline estimates with current practices employed at farms that use NRCS conservation programs. A “no practices” alternative scenario will be run in order to estimate benefits of those programs. Our group provides an independent evaluation of the cropland component of the national-scale CEAP project. As part of the evaluation process, we evaluate how in situ soil water conditions are approximated. A pedotransfer function (PTF) approach is embedded into the APEX model, estimating water retention at -33 and -1500kPa matric potentials using the renowned PTF of Rawls et al. (1982). We revealed that the Rawls et al. PTF delivers sub-optimal and biased estimates for US conditions, for which these equations were widely considered to be valid. This is due to differences in data collection methodologies, incorrect conversion or translation of data into common units or due to the misrepresentation of data when those were in fact missing. Use of an alternative solution and alternative data is being suggested for use.