Soil Drainage Classification Course
Mid-Atlantic Association of Professional Soil Scientists, 2017 Spring Field Day, Evesboro to Elkton – A Day in the Pits.
Leslie and I attended the MAPSS soils class held at the National Plant Materials Center, in Beltsville, MD. The day-long class featured soil test pits that addressed natural drainage classifications, referring to the frequency and duration of wet periods under conditions similar to those under which the soil formed. Classes of natural soil drainage are recognized as excessively drained, somewhat excessively drained, well drained, moderately well drained, somewhat poorly drained, poorly drained, and very poorly drained.
Drainage classes are from observations of water tables, soil wetness, landscape position and soil morphology. In many soils the depth and duration of wetness relate to the quantity, nature, and pattern of redoximorphic features. Redoximorphic features are soil features associated with wetness. They result from the reduction and oxidation of iron and manganese compounds in the soil after saturation with water and desaturation, respectively.
Drainage classes provide a guide to the limitations and potentials of the soil for land development, field crops, forestry, wildlife, and recreational uses. The class roughly indicates the degree, frequency, and duration of wetness, which are factors in rating soils for various uses.
Our instructors for the day included Marty Rabenhorst, Gary Jellick, Robert Bricker, David Verdone, Phil King, Annie Rossi and Barry Glotfelty, and with the in-forest lunch being catered by the Silver Diner of Greenbelt, MD.
Our field notes were as follows:
A reminder of the basics when describing a soil:
- horizon has lots of organic matter barely decayed.
- A horizon has organic matter and mineral materials.
- Ap horizon is plowed, usually 7-8” deep and always has an abrupt boundary.
- E horizon is bleached or whitish. The iron and other minerals, as well as organic materials have been washed out. This layer will not be found where the soil was plowed, but is common in undisturbed acidic forests.
- B horizon is the subsoil, has low organic matter, but other leached materials, like clay accumulate here. There are signs of soil morphology within the B horizon.
- Bt horizon has clay accumulation (argillic horizon)
- Bw horizon is weakly developed and does not have recognizable concentrations (cambic horizon)
- BC horizon has minimal soil development
- C horizon has partially disintegrated parent material and is very uncommon in the Coastal Plain (unless on a floodplain and the parent material is alluvium).
- R horizon is bedrock.
- Ironstone is soil cemented with iron and sulfides. It is not the same thing as sandstone and can be found within the B horizon.
- It takes very little iron to color and coat sands as compared to finer grained soils.
- Old dunes have a chevron shape and are deeper on the downwind side.
Abbreviations used on soil data sheets (soils should always be moist)
- Under texture, s= sand, sl = silt loam or sandy loam, ls= loamy sand
- Under consistency, FR = friable, VFR = very friable, L = loose
- Under structure, 1= weak and 3= strong, SBK = subangular blocky, PL= platy Strong structure can allow for water to move through fine textured soils quickly.
- Under Abundance for redox features, we now should estimate actual percentage, but they used to approximate with F (Few) = <2%, C(Common) = 2-20%, and A (Abundant) = >20%
- Under Contrast for redox features, F (Faint) = the color block is touching the color block for the matrix on the Munsell book, D(Distinct) = obvious, P(Prominent) = very strong
- Under Boundary, a=abrupt (<2cm thick), w=wavy, c=clear (2-5 cm thick), s=smooth, g=gradual
Hydromorphic soils have redox features and include hydric soils.
Concentrations have a high chroma and are often found higher in the soil profile than depletions.
Depletions have a low chroma.
Soil Drainage Classes are determined by where the redox features are found:
- Moderately Well Drained soils have depletions at 50-100 cm below the surface.
- Somewhat Poorly Drained soils have depletions at ? to 50 cm below the surface.
- Poorly Drained soils have gray soils near the surface and are hydric.
- Very Poorly Drained soils have a thick A horizon because they are wet all the time and are hydric.
Here is a handy guide for determining if you have hydric soils (soils that lack field indicators):
- Dig a hole to 6-inches.
- Does organic soil material or mucky modified layer exist?
- Does chroma of 2 or less exist?
- Do you see distinct or prominent redox concentrations as soft masses (mottles) or pore linings?
- Is there hydrogen sulfide odor?
- Check landscape position, are you in a depression, on a floodplain or near a marsh?
If you answer NO to these questions, the soil will NOT meet the indicator.
https://www.soilhub.com/ has a mobile app with Field Guide to Hydric Soil Indicators.
Pines and blueberries tolerate high levels of aluminum. Crop death sometimes occurs when the pH drops below 6 because then aluminum goes into solution and is available to plants.
Old temperature regimes in the soil survey:
- Thermic soils supported the growth of cotton.
- Mesic soils support the growth of corn.
- Frigid soils do not support the growth of corn.
Lamellae are bands where clay accumulated in the Bt or BC horizon in sandy soils due to water moving down through the soils. They feel finer, stickier, and/or firmer than the rest of the horizon.
Marble or limestone soils have clays that form a waxy coating around the peds, which allows water to move quickly through the soil even though it might be a silt clay loam and therefore, the soil perks well. However, if you install the septic field while the soils are wet, the clay smears and you create a clay pond so septic fields should in these soils should only be built when the soils are dry. Maryland has regulations related to this issue, but Delaware does not and relies on professional judgement/liability.
Field notes prepared by:
Mark Burchick and Leslie Wood Mummert
Environmental Systems Analysis, Inc. (ESA)
2141 Priest Bridge Drive, Suite 1
Crofton, MD 21114