RI Soil Survey - Highly erodible soil map units

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Note: All soils have sever erosion hazards when excavated and stockpiled. Erosion control practices should be planned for any human disturbance of an area. Contact the USDA NRCS for information on erosion control.

INTRODUCTION

Natural processes continually create new soil from the underlying raw parent material or from bedrock. For most soils in Rhode Island these processes offset about 3 tons of erosion per acre per year. Erosion rates lower than the rate of soil development are considered "tolerable". Most soils have been assigned a tolerance value, which is based mainly on the thickness of the soil above bedrock or unaltered parent material.

Natural Resources Conservation Service soil scientists and soil conservationists determine if a soil, or soil map unit, is "highly erodible" or "potentially highly erodible" due to sheet and rill erosion. This determination is done by using the Universal Soil Loss Equation (USLE). The USLE relates the effects of rainfall, soil characteristics, and the length and steepness of slope to the soil's tolerable sheet and rill erosion rate.

Definition of Highly erodible soil

A highly erodible soil, or soil map unit, has a maximum potential for erosion that equals, or exceeds, eight times the tolerable erosion rate. The maximum erosion potential is calculated without consideration to crop management or conservation practices, which can markedly lower the actual erosion rate on a given field. The maximum potential erosion rate is determined using the formula: RKLS/R (where R = the rainfall factor, K = erodibility value of the soil, and LS = the slope factor). If RKLS/T > 8 then the soil meets the criteria for a highly erodible soil.

CRITERIA FOR DETERMINING HIGHLY ERODIBLE SOIL MAP UNITS

The procedure for determining whether a given soil map unit qualifies as highly erodible or potentially highly erodible is as follows:

Step 1. For each soil map unit in the soil survey legend, calculate the minimum LS value required for (RKLS/T > 8) by solving for LS. (i.e. LS = 8T/RK).

Step 2. For the specific combinations of slope length and steepness specified in the next two steps, obtain LS values from Table 3 in Agricultural Handbook 537, Dec. 1978.

Step 3. A soil map unit qualifies as highly erodible if the LS value for the shortest length slope in combination with the minimum percent slope (as defined in the map unit description) meets the criteria of RKLS/T >8. (See appendices A-H)

Step 4 A soil qualifies as potentially highly erodible if:
a. The LS value for the shortest slope length, in combination with the minimum percent slope, (as defined in the soil map unit description) is less than 8T/RK.
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b. The LS value for the longest slope length, in combination with the maximum percent slope, (as defined in the soil map unit description) is greater than or equal to 8T/RK.

NOTE:
** For soil map units containing more than one named soil, the map unit listing is based on the most erosive soil.
** Soil map units containing soils that have not been assigned a "K" value were not evaluated, and do not show up on these list. (Examples: beaches, gravel pits, sand dunes, dumps, Udorthents, etc.)
** Soil map units which do not appear on the highly erodible or potentially highly erodible lists, and have been assigned a "K" value, are considered non highly erodible. These soils generally are on nearly level landscapes.

List of Soil Map Units That Qualify as Highly Erodible Land (From the Soil Survey of Rhode Island Correlated and published, 1981)

*  Rocky, very stony, or extremely stony soil map units.  These soils generally are not suited for cultivation without removal of surface stones.  If enough stones are removed to permit regular tillage then the soil map unit designation should be changed to a non-stony phase.

List of Soil Map Units That Qualify as POTENTIALLY Highly Erodible Land (From the Soil Survey of Rhode Island Correlated and published, 1981)

* = Rocky, very stony, or extremely stony soil map units.  These soils generally are not suited for cultivation without removal of surface stones.  If enough stones are removed to permit regular tillage then the soil map unit designation should be changed to non-stony phase.

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