Green Horizons

A frequently asked question at Natural Resources Conservation Service (NRCS) field offices around the state is: “What is a good walnut soil?”

Current NRCS information rates soils only as “suitable” or “unsuitable” for black walnut. We have recently led a team that has developed a more extensive model that uses 12 soil and site factors from the National Soil Information System database (NASIS). This interpretive model generates a Black Walnut Suitability Index (BWSI) for each soil component within each soil survey map unit. It is a rational, objective method of rating soils based on their inherent potential for black walnut growth.

Currently, the BWSI is available only for Missouri soil map units.

Soil properties in the model include effective soil depth, available water capacity, water table depth, percent clay, percent sand, pH and surface rock fragments. Site properties include flood frequency and duration, position on the landscape and historic native vegetation.

A computer model converts the NASIS values for these soil and site properties into numeric scores on a continuous scale from 0 to 1, with higher values indicating better suitability. The model then weights these values according to their relative importance for growing high-quality walnut and a composite score is then used to group the soil into one of six suitability classes: unsuited, poorly suited, somewhat suited, moderately suited, well suited and very well suited.

One can access the BWSI from two NRCS Web sites. One site is low-tech and produces only tabular information. It also requires you to know the specific soil series you wish information about. The other site is high-tech and produces an interpretive map as well as tabular information. You do not need specific soil series information as for the other Web site. All you need to know is where you want to go and you can “fly” directly to your property using the site’s GIS (geographical information system).

Both Web sites work best using high-speed internet access, especially the GIS-based site. Also, for both sites, be sure that you turn off any pop-up blockers.

The low-tech option is the Soil Data Mart (http://soildatamart.nrcs.usda.gov/). Upon entering the Web site: (1) select Missouri (remember that the BWSI is only available for Missouri at this time), (2) select your county of interests, (3) click ‘Generate Report’ button, (4) select your five-digit soil map unit ID and the “Selected Soil Interpretations” from the drop-down report menu, (5) click ‘Generate Report’ button, (6) select the “FOR-Black Walnut Suitability Index” from the Soil Interpretation Name menu, (7) click "Generate Report" button, (8) print or save resulting PDF file.

The high-tech option is the Web Soil Survey (http://websoilsurvey.nrcs.usda.gov/app/). Upon entering the Web site: (1) click the green ‘Start WSS’ button at the top of the page, (2) the ‘zoom’ feature will be active, so simply select an area in Missouri, (3) find your area of interest using the zoom and grab features on the toolbar, (3) click on either the rectangle or polygon AOI button to generate an Area of Interest, (4) click on the ‘Soil Data Explorer’ tab along the top of the page, (5) open the ‘Vegetative Productivity’ drop-down menu to the left and select the Black Walnut Suitability Index, (6) click ‘View Rating’ button, (7) click the ‘Printable Version’ button at the top of the page, (8) print or save the resulting PDF .le. This site asks that you use the ‘Logout’ button at the top of the page to properly exit the site. If you do not log out, upon entering the WSS from the same computer or internet portal, you will be placed at your previous AOI. GH

For more information or help navigating either Web site, contact Doug Wallace at (573) 876-0908, doug. wallace@mo.usda.gov or your nearest NRCS field office.