The United States has been divided by the NRCS (1983) into categories
of major land resource regions and major land resource areas (MLRA). MLRAs
are geographically associated land resource units and have been used in
state, regional and national agricultural planning and in natural resource
assessment. A major land resource region combines those MLRAs that can
be grouped regionally. MLRAs are useful as a basis for making decisions
about national and regional agricultural concerns, identification of research
needs and resource inventories, a broad base for extrapolating the results
of research within national boundaries, and serve as a framework for organizing
and operating resource conservation programs (NRCS 1981).
The map of the MLRAs for the southern region of the United States was
developed from the patched version of the STATSGO digital database of the
United States. The STATSGO database was designed primarily for regional,
multi-state, watershed, state and multi-county resource planning, management,
and monitoring. The digital file containing the MLRAs was reclassed based
on the individual MLRAs selected in this work. A mask of each MLRA was
developed to partition each MLRA from other areas. The areal extent of
each MLRAs in the southern region was approximated by developing a report
with the respective mask using the GIS software GRASS.
Locations of the major land resource regions and MLRAs for the southern
region of the United States are shown in Fig. 1. Seven major land resource
regions were identified in the southern region of the United States. The
areal extent of the 20 MLRAs in which data are reported in this bulletin
and the states in the southern region in which they occur are presented
in Table 1. The three most extensive MLRAs
are 133A, 136 and 133B. The Southern Coastal Plains (MLRA 133A) occupies
about 275,000 km2 and occurs in eight states in the region.
The Southern Piedmont (MLRA 136) is the second most extensive MLRA and
occupies about 167,000 km2 in the five states adjacent to MLRA
133A. The third largest MLRA is the Western Coastal Plains (MLRA 133B)
which occupies about 137,000 km2 and occurs in four states in
the western portion of the region. The list also includes five MLRAs that
occupy less than 25,000 km2. These relatively small MLRAs include
the Nashville Basin in Tennessee, the Blackland Prairies in Alabama, Mississippi,
and Arkansas, the Sand Hills in North Carolina and South Carolina, the
Sand Mountains in Alabama and Georgia, and the Texas Claypan area in Texas.
Collectively, the MLRAs chosen in this work occupy almost 1.45 million
km2 and about 65.8% of the land area in the southern region
of the United States.