This website is designed to help you calculate the Drainage Index (DI) and Productivity Index (PI) of all soils that are classified within the US system of Soil Taxonomy. These data aid in the identification of areas at risk to various forest insects and diseases because of their ability to identify regions of potential tree stress (see the 2013-2027 National Insect and Disease Forest Risk Assessment).
For help with this taxonomic system, please visit the official NRCS Soil Taxonomy page. This work was performed under the supervision of Dr. Randall Schaetzl, Department of Geography, Michigan State University, under contract with (and supported by) the US Forest Service.
Please note that the tabular information provided on this site has been updated using the 2016 SSURGO database.
The Drainage Index (DI), originally named the "natural soil wetness index" (Hole and Campbell 1986, Schaetzl 1986), is a measure of long-term soil wetness. It is designed to represent, as an ordinal number, the amount of water that a soil contains and makes available to plants under normal climatic conditions. It is not meant to mimic the concept of "plant available water", which is mostly dependent upon soil texture. The DI only loosely/secondarily takes soil texture into consideration. The main factor affecting the DI is the depth to the water table and the soil volume available for rooting, for a plant can get at this form of water readily. The DI concept was first initiated by Hole (1978) and Hole and Campbell (1985), and expanded upon by Schaetzl (1986).
The DI ranges from 0 to 99. The higher the DI, the more water the soil can and does, theoretically, supply to plants. Sites with DI values of 99 are essentially open water. A soil with a DI of 1 is as thin and dry as bare bedrock. The DI is derived from the soil's taxonomic subgroup classification in the US system of Soil Taxonomy, and (optionally) its soil map slope class. Because a soil's taxonomic classification is not (initially) affected by such factors as irrigation or artificial drainage, the DI does not change as soils become irrigated or drained (unless the long-term effects of this involve a change in the soil's taxonomic classification). Instead, the DI reflects the soil's NATURAL wetness condition. Each soil SERIES has, in theory, its own unique DI. Some soil series span two or more drainage classes; in this case the DI that is used is the one that would normally be used for a soil with that subgroup classification.
This website contains tools to interactively select DI based on known soil taxonomy (or to "look up" the taxonomic Subgroup for a known DI), as well as an interactive map of DI for the United States.
Schaetzl, R.J., Krist, F.J. Jr., Stanley, K.E., and C.M. Hupy. 2009. The Natural Soil Drainage Index: An Ordinal Estimate of Long-Term, Soil Wetness. Physical Geography 30:383-409. (Adobe PDF, 3.5 MB)
Like the DI, the Productivity Index (PI) is an ordinal measure, but of the productivity of a soil. The PI uses family-level Soil Taxonomy information, i.e., interpretations of taxonomic features or properties that tend to be associated with low or high soil productivity, to rank soils from 0 (least productive) to 19 (most productive). The index has wide application, because, unlike competing indexes, it does not require copious amounts of soil data, e.g., pH, organic matter, or CEC, in its derivation. GIS applications of the PI, in particular, have great potential. For regionally extensive applications, the PI may be as useful and robust as other productivity indexes that have much more exacting data requirements
This website contains tools to interactively select PI based on known soil taxonomny, as well as an interactive map of PI for the United States.
Schaetzl, R.J. Krist, F.J. Jr., and B.A. Miller. 2012. A Taxonomically Based, Ordinal Estimate of Soil Productivity for Landscape-Scale Analyses. Soil Science 177:288-299. (Adobe PDF, 7.1 MB)