Quantifying Soil-Landscape Relationships to Create Functional Maps and Methods for Scaling Soil Data.

For more than 60 years, field soil scientists in the U.S. have used the concept of the five soil forming factors to create maps of soil polygons with discrete boundaries between soil mapping units. The taxonomic heterogeneity has been represented by the range of soil property values between and within map units with no representation of the continuum of soil property values. Currently with high quality DEM’s, Online Soil Survey (SSURGO), geographical information systems (GIS) and powerful geo-referencing tools, the specific geo-referenced spatial location can be used to understand soils. Additionally, recent advances in terrain-based digital soil mapping allow us to take a new approach of mapping soils based on their functional similarities rather than the taxonomic heterogeneities. Discrete soil property values associated with each soil polygon are weighted by their "influence" based on their fuzzy membership values to generate continuous functional soil property maps rather than discrete taxonomic soil map units. For this study, areas with similar geomorphology were segregated to capture random variability, then terrain-based soil mapping was used to quantify the topographically controlled systematic variability. Soil Landscape Interface Model (SoLIM) and Knowledge Miner softwares were used for this research. Within a training area, the SSURGO soils data and terrain attributes were extracted to develop quantitative frequency distributions for setting rules within SoLIM.  The relationship was applied to the landscape to create a soil map in raster format.  Each pixel was assigned a unique value based on lab data and expert knowledge to represent the soil-landscape continuum. These techniques were used to create maps of soil organic carbon and hydrology parameters. The maps were validated using 300 georeferenced points. This method is based on fundamental soil forming processes and enables soil scientists to extrapolate small scale studies to larger landscapes.