Documentation for mean bulk density,
Geographic (latitude/longitude) coordinates

This dataset contains the mean bulk density for each of 11 standard soil layers for the 48 conterminous states derived from the State Soil Geographic (STATSGO) soils data compiled by the Natural Resources Conservation Service (NRCS) of the U.S. Department of Agriculture.

  1. Overview
  2. Processing methodology
  3. Units of measurement
  4. Projection and georeferencing information
  5. Description of dataset files


Cautions:

For many STATSGO components, a depth-to-bedrock value of 60 inches (152 cm) was used to indicate that the soil was sampled only to this depth, and no bedrock was encountered. As a result, for many map units an entry of "bedrock" for the two lowest standard layers (1.5 to 2.5 m) may actually indicate "no data".

A number of non-water components, and in some cases entire map units, have BDL = BDH = 0 for all component layers, even though other variables for the layer (e.g., texture) contradict the BD values. These components were ignored in the computation of average values for the map unit. If BDL = BDH = 0 for all non-water components for the map unit, the BD value was set to 0 and the porosity to a flag value, 1.01. If the map unit is entirely water, BD is set to zero and the porosity to 1.00.


Overview

Bulk density is defined as the total mass of soil per unit volume. It is determined from the STATSGO Layer table variables BDH and BDL.

This dataset was created by computing the mean bulk density for each layer of each component of each STATSGO map unit, and interpolating the results to a set of 11 standard layers. The results for each of the 48 conterminous states (map units for the District of Columbia are included under Maryland) wre joined to create a single dataset.

To increase compatability with different types of data analysis software, the dataset is available in several different data file formats. These include both Arc/Info polygon format and a gridded version at 30 arc-second resolution; the latter is available in both Arc/Info grid format and as a three-dimensional array of 16-bit binary integers, representing the bulk density value multiplied by 100. The description of dataset files provides additional details on formats, the data files asociated with each format, and instructions for file retrieval.

For the gridded version of the dataset, any 30-arcsecond grid cell which contains portions of two or more map units was assigned the mean bulk density values of the map unit which occupies the largest fraction of the cell. For the Arc/Info grid version, the mean bulk density value for each layer may be accessed using the map unit serial numbers associated with each STATSGO map unit; the bulk density data have been incorporated into the Value Attribute Table (VAT) entry for each map unit.

This dataset is in geographic (latitude/longitude) coordinates. Note that the same data are also available in the Albers equal area projection which was used by the NRCS for compiling the STATSGO data and in the Lambert azimuthal equal area projection used by the USGS and the EROS Data Center for a number of other datasets covering the 48 states.

Units of measurement

Bulk density values are given in g/cm³.


Last change: 29 Sep 1997, R. A. White / raw@essc.psu.edu