Each soil group is designated on the Natural Soil Group Map by a capital letter and a number, such as B1. If a group contains soils that have a wide range in slope, then the group is subdivided into slope ranges indicated by the addition of a lower case letter such as B1a. A lower case letter a means that slopes range from 0 to 8 or 10 percent; b - 8 to 15 or 10 to 15 percent; and c - steeper than 15 percent. On the Eastern Shore, practically all soils mapped have slopes of less than 10 percent; therefore, to reduce map clutter, only the capital letter and number are designated for soils on the Eastern Shore, For example, Bl on the Eastern Shore and B1a in the Piedmont region both indicate soils in Group B1 with slopes of 0 to 10 percent.
The Natural Soil Group symbols are not connotative, although the lower case letters a, b, and c indicate specific slope ranges. In general, the Natural Soil Groups are arranged in order of increasing limitations or problems for most uses. Drainage class or wetness is one of the prime considerations in land use. Thus, the system is connotative in that the soils, in general, get progressively wetter moving from A to G in the alphabet. Also, in general, the number designation indicates the intensity of an unfavorable feature such as wetness, droughtiness, or very high or low permeability. For example, the soils in Group A are sandy and droughty, but Al is not so droughty as A2. The soils in Groups B1, B2, and B3 are all deep and well drained, but have progressively slower permeability. Thus, the numbers indicate increasing limitations within the capital letter designation. In most groups, the numbers represent increasing limitations of permeability.
Table. Estimated physical and chemical properties of Natural Soils Groups of Maryland (Maryland Office of Planning, 1973)
| SOIL | DEPBED | DEPWAT | DEPSOL | TEXTUR | EROK | HYDGRP | IRRMAX | PERMAX | PERC | AWC | PH |
|---|---|---|---|---|---|---|---|---|---|---|---|
| A1,A1a,A1b,A1c | 72+ | 4+ | 0-60 | loamy sand; sand, sandy loam | 0.17 | A | 1.00 | >6.0 | <45 | 0.2-0.6 | 4.0-5.0 |
| A2 | 72+ | 1-10 | 0-60 | sand | 0.17 | A | N/A | >6.0 | <45 | <0.06 | 5.0-8.0 |
| B1,B1a,B1b,B1c | 72+ | 3+ | 0-60 | silt loam,loam, fine sandy loam, sandy loam, silty clay loam, clay loam,silty clay, clay | 0.32 | B | 0.4-0.6 | 0.6-2.0 | 45-60 | 0.12-0.24 | 4.5-6.5 |
| B2,B2a,B2b, B2c | 72+ | 4+ | 0-60 | silt loam, loam, gravelly loam, clay loam,silty clay loam | 0.43 | C | 0.3-0.4 | 0.2-0.6 | >60 | 0.12-0.24 | 4.5-7.3 |
| B3 | 72+ | 5+ | 0-60 | clay, silty clay, silt loam, loam,loamy sand | 0.37 | C | 0.3 | <0.6 | >60 | 0.06-0.24 | 4.0-5.0 |
| C1,C1a,C1b,C1c | 20-40 | In bed-rock | 0-40 | silt loam, loam, shaly silty loam, shaly loam, channery loam, channery silt loam, sandy loam | 0.22 | C | 0.3 | 0.6-6.0 | >60 | 0.12-0.24 | 4.-7.3 |
| C2 | 20-40 | 3+ | 0-40 | silty clay loam, silty clay, clay | 0.37 | C | 0.3 | <0.6 | >60 | 0.12-0.24 | 5.0-7.5 |
| D1,D1a,D1b, D1c | <20 | In bed-rock | 0-20 | shaly silt loam, shaly loam, silty clay loam, silty clay | 0.28 | C-D | 0.3 | 0.6-6.0 | 45-60 | 0.18-0.24 | 4.0-7.3 |
| E1, E1a,E1b | 72+ | 1.5-2.5 | 0-60 | sandy loam, sandy clay, loam, loamy sand, sand | 0.28 | C | 0.4-0.6 | 0.6-6.0 | <60 | 0.12-0.24 | 4.0-5.0 |
| E2,E2a,E2b | 72+ | 1-3 | 0-60 | silt loam, loam, silty clay loam, fine sandy loam, sandy clay loam | 0.43 | C | 0.3-0.4 | <0.6 | >60 | 0.12-0.24 | 4.0-6.5 |
| E3, E3a, E3b | 72+ | 1.5-2.5 | 0-60 | silt loam, loam, silty clay loam | 0.37 | C | 0.4 | 0.2-0.6 | >60 | 0.18-0.24 | 4.5-5.5 |
| F1 | 72+ | 0-1 | 0-60 | loamy sand, sand | N/A | D | 1.0 | >60 | <45 | <0.06 | 3.5-5.0 |
| F2 | 72+ | 0-1 | 0-60 | sandy loam, fine sandy loam, sandy clay loam, loam, loamy sand | 0.28 | D | 0.4-0.6 | 0.6-2.0 | <60 | 0.12-0.24 | 4.0-5.0 |
| F3 | 72+ | 0-1 | 0-60 | silty clay loam, silty clay, clay, loam, silt loam | 0.43 | D | 0.3 | <0.6 | >60 | 0.18-0.24 | 4.0-7.8 |
| G1,G1a | 72+ | 3+ | 0-60 | silt loam, loam, fine sandy loam, sandy loam, silty clay loam | N/A | B-C | 0.5-0.7 | 0.2-2.0 | 45-60 | 0.12-0.24 | 4.0-7.3 |
| G2 | 72+ | 0-1 | 0-60 | silt loam, silty clay loam, silty clay, fine sandy loam, sandy loam, loam, muck | N/A | D | 0.5 | 0.6-6.0 | 45-60 | 0.18-0.24 | 4.0-7.3 |
| G3 | 72+ | 0 | 0-60 | variable | N/A | N/A | N/A | Var. | Var. | Var. | 3.5-9.0 |
| H1,H1a,H1b,H1c | Too variable to rate. Determine the specific soil series name from detailed soil map and use the information for the group that the series is in. | ||||||||||
| H2,H2a,H2b,H2c | Too variable to rate. Determine the specific soil series name from detailed soil map and use the information for the group that the series is in. | ||||||||||
EXPLANATION
DEPBED = Depth to bedrock (in.) -- distance from the surface of the soil downward to the surface of the rock layers. Soils were observed only to a depth of 6 feet: greater depths are specified at 72+ in.
DEPWAT = Depth to water table (ft) -- distance from the surface of the soil downward to the highest level reached In most years by ground water.
DEPSOL = Soil depth (in.) -- this does not imply that the soils are only 60 in. deep, but rather that the estimates In the table are for the 0-60 in. depth and not below.
TEXTUR = Dominant texture -- relative percentages of sand, silt, and clay in a soil sample. If the soil contains gravel or other particles coarser than sand, then an appropriate modifier Is added.
EROK = Erodibility (K factor) -- a measure of the susceptibility of bare soil to erosion and the same K factor as that used in the Universal Soil Loss Equation (Wischmeier and Smith, 1965).
HYDGRP = Hydrologic Soil Group -- a measure of the runoff potential of soils, when fully saturated. Group A soils have the lowest potential and D soils the highest.
IRRZMAX = maximum irrigation rate (in/hr)-- maximum rate of irrigation water applied by sprinklers.
PERMAX = Permeability (in/hr) -- rate at which soil transmits water while saturated. Permeability rates shown are based on the least permeable section of the soil.
PERC = Percolation (min/in) -- rate at which water can move through a soil with moisture at field capacity.
AWC = Available Water Capacity (in/in) -- the difference between the amount of water in the soil at field capacity and the amount in the soil at the wilting point of most crops.
PH = Reaction (pH) -- the degree of acidity or alkalinity of a Soil group, expressed in pH units.
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