Houston black soil extends over 1,500,000 acres (6,100 km2) of the Texas blackland prairies and is the Texas state soil. The series is composed of expansive clays and is considered one of the classic vertisols. 
Houston black soils are used extensively for grain sorghum, cotton, corn, small grain, and forage grasses. In their natural state, they support mostly tall and mid grass prairies of big bluestem ( Andropogon gerardi), sideoats grama ( Bouteloua curtipendula), switchgrass ( Panicum virgatum), little bluestem ( Schizachyrium scoparium), and indiangrass ( Sorghastrum nutans), with some elm (Ulmus spp.), hackberry ( Celtis spp.) and mesquite ( Prosopis glandulosa) trees.   The soil also shrinks and swells with variations in how much water it contains.  In the USDA taxonomic system it is designated an "Udic Haplusterts". 
- "Houston Black -- Texas State Soil". US Department of Agriculture Natural Resources Conservation Service. Retrieved 2013-02-06.
- "Houston Black Series". National Cooperative Soil Survey. United States Department of Agriculture. Retrieved 2013-02-06.
- "Houston Black: Proposed State Soil for Texas". US Department of Agriculture Natural Resources Conservation Service. Archived from the original on 2010-10-08. Retrieved 2010-11-11.
- "Houston Black -- Texas State Soil". University of Illinois Urban Resources. Retrieved 2010-11-11.
- "What on Earth is Houston Black Soil?" (pdf). US Department of Agriculture Natural Resources Conservation Service. February 2003. Retrieved 2010-11-11.[ permanent dead link]
|This agriculture article is a stub. You can help Wikipedia by expanding it.|