Soil Surveys. What are the most important properties to consider in a taxonomic system used for making a soil survey?

Transcription

1 Soil Surveys What are the most important properties to consider in a taxonomic system used for making a soil survey?

2 What is a Soil Survey? Inventory of soil resources Delineation of spatial distribution of soil properties

3 Two Types of Soil Surveys Taxonomic (based on a range of soil properties, has broad application) Interpretive (soil survey for a single use)

4 Soil Taxonomy (hierarchical system) Order broad, least detail Suborder Great Group Subgroup Family Series---most detail

5 Soil Survey of Rhode Island Uses the USDA-NRCS classification system (Soil Taxonomy) Taxonomic level for the soil survey is generally at the series level, example would be a Ridgebury soil

6 Ridegebury Family Taxonomic Class Loamy, mixed, mesic, shallow Aeric Endoaquepts Loamy: between a depth of 25 and 100 cm (10-40 ) average clay content is <35%, not sandy Mixed minerals in course silt and fine sand are not dominated by a particular mineral Active has a moderate charge capacity to clay ratio Mesic moderate climate like we have Shallow restrictive layers are within 50 cm (20 ) Aquept --soil has a Bw or Bg horizon and depletions within 50 cm of the soil surface Endo wets from the bottom up Aeric--chroma of greater than or equal to 3 below the A horizon

7 Ridgebury Series-level Criteria Somewhat poorly and poorly drained soils formed in till derived mainly from granite, gneiss and schist commonly shallow to a densic contact mean annual precipitation is about 45 inches slope <15%

8 Ridgebury Range in Characteristics Rock fragments range from 5 to 35 percent by and are subangular fragments unlimed soil ph ranges from very strongly acid through moderately acid O horizon has hue of 7.5YR to 2.5Y, value of 2, 2.5, or 3 and chroma of 0 to 2. A or Ap horizon has hue of l0yr to 5Y, value of 2, 2.5, or 3 and chroma of 0 to 2. E horizons have a hue of 10YR to 5Y, value of 4 to 6, and chroma of 1 or 2 B horizon has hue of 7.5YR to 5Y, value of 4 to 6, and chroma of 0 to 4. Chromas of 3 or 4 are restricted to subhorizons. Textures are sandy loam, fine sandy loam or loam. Redoximorphic features are few to many and distinct or prominent. B horizon has subangular blocky structure, weak to moderate very thin to medium platy structure or is massive. It is very friable or friable. Cd layer has hue of l0yr to 5Y, value of 3 to 6, and chroma of l to 4. There are distinct or prominent redoximorphic features that become less abundant with depth. Texture is coarse sandy loam, sandy loam, fine sandy loam, very fine sandy or loam. Consistence is firm or very firm and brittle. Structure shape is massive or platey.

9 For our purposes are all these important? Probably not, so what is important? Parent material Texture Slope Depth to restrictive layer Depth of the seasonal high water table

10 Parent Materials Outwash Ice-contact stratified drift Loose till Dense till Loess Alluvium- Eolian sands- Human transported materials (HTM) Residuum Organic deposits

11 Stratified sands and gravels Deposited south of the melting ice along broad flats by braided streams leaving the ice Particles are often rounded or subrounded Particle size of individual layers dependent on energy of the braided stream Typically have a high saturated hydraulic conductivity (Ksat) Outwash

12 Ice-contact Stratified Deposits Form on or under the ice Landforms are eskers, kames, and kame terraces Mostly stratified materials, although often contains larger fragments Eskers often contain large fragments

13 Wind blown deposits following deglaciation Dominated by silt-sized particles Likely covered most of Rhode Island, most prevalent in southern part of the state What remains are typically a foot to 5 feet thick Thick deposits over outwash support turfgrass and sod production in the state Loess

14 Forms as the ice melts and materials settle not far from stagnant ice Sometimes referred to as melt-out or ablation till Contains a large range of particles in no particular order (unpredictable) Typically has moderate to high saturated hydraulic conductivity Loose Till

15 Forms at the base of the advancing ice Sometimes referred to as lodgement or basal till Contains a large range of particles in no particular order (unpredictable) Typically has low to very low saturated hydraulic conductivity Often has perched water tables during parts of the year Dense Till

16 Restrictive Layers Bedrock (ledge) Densic materials dense till Hydraulicly Limiting Difficult or impossible to excavate

17 Fine earth fraction (particles less than 2 mm) Particle-Size Distribution Clay Silt Sand Rock fragments (>2 mm) Gravels Cobbles Stones Boulders

18 Particle-Size Distribution (Texture) In most cases dictates Ksat Controls how easy the materials are to work with in regards to moving and excavation Problems with smearing Use as a road subgrade

19 Textural Classes: Soil scientists use the USDA system Loamy sand Fine sandy loam Gravelly sandy loam

20 Slope What does it affect? Surface Runoff Lateral Flow Stability Where equipment can be used