Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 18, 2009
Publication Date: July 1, 2009
Repository URL:http://hdl.handle.net/10113/36072 Citation: Nemes, A., Timlin, D.J., Pachepsky, Y.A., Rawls, W.J. 2009. Revision of the Rawls et al. (1982) pedotransfer functions for their applicability to US croplands. Soil Science Society of America Journal. 73:1638-1645.
Interpretive Summary: The U.S. Department of Agriculture conducts a national assessment of environmental benefits and effects of 2002 Farm Bill programs. As part of the mandated evaluation process, we evaluated how soil water conditions in the field are estimated using laboratory data and mathematical equations. A well-known estimation technique – published in 1982 - was originally suggested for use, but we found that it was built on errant data and that it uses an estimation technique that is outdated. We suggest using improved soils data and a more complex alternative estimation technique. Utilizing the recommended changes, field soil conditions will be simulated more realistically, and as a result, agricultural production and its impact on the environment can be accessed more accurately. Successful completion of this project will equip lawmakers and regulatory agencies with better tools and measures to help promote sustainable agricultural practices, which is in the interest of the general public.
Large scale environmental impact studies typically involve the use of simulation models and require a variety of inputs, some of which may need to be estimated in absence of adequate measured data. As an example, soil water retention needs to be estimated for a large number of soils that are to be used in the context of the U.S. national scale Conservation Effects Assessment Project. Use of a set of well known linear regression based pedotransfer functions (PTFs) were proposed in 1982 to address that data need. Examination of the underlying data as well as comparative estimations to an independent U.S.-wide data set revealed that the proposed equations were meant to use organic carbon (OC) data in place of the reported organic matter (OM) data. Other discrepancies – possible misreportings – were also found in a significant portion of the OM data. These PTFs were also developed from data originating from only 18 U.S. states - and 48% of them originated from only 3 U.S. states - while major cropland states/regions were barely represented or not represented at all. Resulting estimations showed non-random distribution of estimation residuals (i.e. bias) that could only be corrected after data transformations and with the use of a more advanced PTF technique. We recommend that the PTF equations proposed in 1982 are not used in the context of the national scale CEAP project. An alternative solution should be sought and care should be taken to ensure the proper representation of U.S. soils and their properties.