Quantifying map unit composition for quality control in soil survey Conference Paper uri icon


  • Characterizing soil spatial variability in soil surveys is critical for maintaining user confidence and soil survey credibility. The purpose of this investigation was to examine the use of USDA-SCS map unit concepts for portraying soil spatial variability and then demonstrate methods for displaying map unit composition in soil survey reports. We examined the composition of four consociation map units in Brazos County, located in the Tertiary Gulf Coastal Plain of Texas. The point-intercept transect method and binomial probability and classical statistical procedures were employed. In all but one case, sufficient observations were obtained to estimate the compositions within ± 15% of the mean at the 80% probability level. Results showed that taxonomic purities of the reference taxa ranged from highs of 49 and 45% for the Crockett (Udertic Paleustalfs) and Spiller (Udic Paleustalfs) series, respectively, to lows of 21 and 11% for the Robco (Aquic Arenic Paleustalfs) and Rader (Aquic Paleustalfs) series, respectively. The concepts of similar and dissimilar soils, as they related to the major land uses of the area, were used to establish interpretive groupings. Subsequent interpretive purities of the Crockett and Spiller improved to 86 and 81%, while the Robco and Rader improved to 52 and 48%, respectively. The Robco and Rader did not meet the criteria for consociations and were therefore designed as multitaxa map units. Because the named components of these units did not occur in a consistent, coterminous pattern from delineation to delineation, a complex map unit could not be designed. We are therefore proposing the implementation of a new map unit concept to accommodate these conditionalities.

published proceedings

  • SSSA Special Publication (Soil Science Society of America)

author list (cited authors)

  • Nordt, L. C., Jacob, J. S., & Wilding, L. P

publication date

  • January 1, 1991 11:11 AM