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The Variability of the Boundary Line Between Soil Survey Mapping Units. Dustin Hancock Why is this research important? Methods Results The accuracy of a soil survey’s mapping unit properties is Two map units were selected for study in Jefferson County, West From the properties (texture, hue, value, chroma, textural class, vital in determining the appropriate agricultural management Virginia. These map units were located on Tabler Farm, which is pH, and horizonal depth and thickness) analyzed, the boundary practices, forestry techniques, or community planning owned by Shepherd College (Fig.1). The FbB mapping unit was line between mapping unit FbB and DgB established by the soil strategies. Inaccuracy in a soil survey's mapping unit composed of soil from the Frankstown taxonomic series, which survey was determined to be outside of the transect sampling area properties may have a negative impact on the health of the is characterized by deep and very deep well drained, moderately or could not be determined due the transition of soil properties soil and the economic viability of the operation taking place permeable soils formed in residual materials derived from over an area larger than the transects used in the study. on it. siliceous limestone and interbedded limy shale. The DgB Frankstown series percent accuracy for averaged transect data of Introduction mapping unit was composed of soil from the Duffields taxonomic series, which is characterized by deep to very deep the Ap horizon for 9 out of 10 points was 37.5% (Fig. 3). The Bt1 horizon increased in accuracy from 81.25% at 10 feet from the Soil surveys are maps and data that give a range of well drained, moderately permeable soils formed in residuum boundary established by the soil survey, to 100% at 90 feet from properties for a particular soil taxonomic unit, with the aim from limestone bedrock Two transects were selected that ran in the boundary line in the Duffields DgB mapping unit (Fig. 4). of determining the spatial extent of map units with similar a southeasterly direction from the top of a slope where mapping Duffields’ series percent accuracy for averaged transect data of the taxonomic properties within a landscape. The most unit FbB was located, to the bottom of the slope where mapping Ap and Bt1 horizons showed a increase from 75% at 10 feet from meaningful soil maps constructed are those that diminish unit DgB was located. These transects were 180 feet long with the established boundary for both the Ap and the Bt1 horizons, to internal heterogeneity within mapping units. This is approximately 90 feet of each transect being located within each 94% and 100% respectively at 90 feet from the boundary line in accomplished through the conveying of the central mapping unit (Fig.2). Samples the Duffields’ DgB mapping unit (Fig. 3 & 4). tendencies and variations around central tendencies of the were taken along transects at 20 soil properties within a mapping unit. The accuracy of soil feet intervals with a total of 10 represents the mapping unit Percent Accuracy of Frankstown and Duffields Series for Averaged Ap Horizon Transect Data Percent Accuracy of Frankstown and Duffields Series for Averaged Bt1 Horizon Transect Data within series range within series range % of properties % of properties 100 110 surveys varies greatly depending on the sampling methods boundary set by the soil 90 80 Frankstown Ap 100 90 Frankstown Bt1 sample holes per transect. At survey. 70 60 50 Duffields Ap 80 70 60 Duffields Bt1 and techniques used to construct the map, along with the each hole samples were taken represents samples that fit soil 40 30 20 50 40 30 20 10 10 resources available and the needs of the users in the area. of the Ap and Bt1 horizons. Soil survey description with a 0 Top of Slope 90 70 50 30 10 10 30 50 70 90 Bottom of Slope (Frankstown) (Duffields) 0 Top of Slope 90 70 50 30 10 10 30 50 70 90 Bottom of Slope (Frankstown) (Duffields) 85% accuracy. Feet Feet Map orders, which are determined by the level of detail, observations and samples were Figure. 3 Figure 4 range from a high of 1:1000-1:15,000 to a low of 1:250,000-1:10,000,000, with second-order county soil taken with a soil auger. Field Fig.1 tabler Farm,Shepherdstown. (WVExplorere.com) Discussion observations included soil The fact that a boundary line between mapping units, which surveys published by the NCSS being the most common. structure, color, and horizonal correlated with the boundary established by the soil survey, These second order surveys are georeferenced orthophotos depth and thickness.All samples could not be discerned suggests that the soil landscape is highly with a scale of 1:20,000 and a minimum size delineation of were analyzed in the Shepherd variable, and only a small portion of that variability is 1.6 ha. Limitations of these surveys include presence of College Soils Laboratory for represented in soil survey reports. The accuracy of mapping unit inclusions, lack of mechanisms to quantify spatial color (hue, value, and chroma), boundaries in the Jefferson County Soil Survey may limit its variability, and uncertainty of the accuracy of the pH, and textural class. effectiveness for technical users, but it is an invaluable tool for taxonomic mapping unit boundaries. This study addressed The percent accuracy for both non-technical users, such as farmers and homeowners. One of the accuracy of mapping unit boundaries in order to the Frankstown and Duffields the main factors in determining the accuracy of a soil survey is Fig. 2. Transects used in the study. (Jefferson County soil Survey, 1973 determine if taxonomic classes adequately define variability taxonomic series was the needs of the users in the area. When the Jefferson County within and among soil mapping units. determined by the number of soil properties (texture, hue, value, Soil Survey was developed in 1973, it met the needs of the large chroma, textural class, pH, and horizonal depth and thickness) that number of farmers in county. Now with the large influx of Research Objectives were found within the ranges established by the soil survey at each point along the transect. Percent accuracy for the two soil series were development in the county, new surveys may need to be developed that characterize map units statically to the fullest •To determine the variability of the boundary line between compared over the transects to determine where the boundary line extent possible. Jefferson County Soil Survey mapping units FbB and DgB. between the two series was located. •To determine if the boundary line between the soil mapping Research Conclusions units is within 99 feet of the boundary line established by the •The soil landscape is highly variable, and only a small portion soil survey. of that variability is represented in soil survey reports. •Technical users of the soil survey need more detailed soil maps.
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