Prevalence of Highly Erodible Land (HEL) and Implications for Pennsylvania

Soil erosion control needs to be a priority for every Pennsylvania farmer. In a year, sheet and rill erosion, as well as ephemeral and classic gully erosion can wash away many tons of topsoil from an acre of land, which means permanently losing one of the most important resources for production. The threat of soil loss is greatest on Highly Erodible Land (HEL). Ninety percent of Pennsylvania cropland is either HEL or potentially HEL, showing the importance of soil erosion control in our state. By implementing a conservation plan or conservation system, producers can greatly reduce potential soil loss from farmland by using ACT practices (practices that Avoid, Control, and/or Trap sediments). ACT practices include such things as no-, or reduced tillage, cover crops, contour farming, strip cropping, conservation crop rotations, terraces, grassed waterways, and sedimentation basins.  

HEL is land that can erode at an excessive rate because of certain soil properties (soil texture and depth), slope steepness and length, and the amount of rainfall. If you participate in a United States Department of Agriculture (USDA) program an HEL determination will have been made for all your crop fields. To enable program participation, a crop field that is determined to be HEL must be managed under an approved conservation plan or conservation system that would prevent water, wind, and ephemeral gully erosion.

An HEL determination is made by applying the Universal Soil Loss Equation (USLE)¹ to calculate the erodibility index (EI) of each soil type. USLE was developed in 1954 using federal-state cooperative research projects at 49 locations and including more than 10,000 plot-years of basic runoff and soil loss data. The EI uses a rainfall and runoff factor (R), the susceptibility of the soil to water erosion factor (K), the combined effects of slope length and steepness (LS), and the soil loss tolerance factor (T).  The T-factor represents the maximum annual rate of soil erosion that could occur without causing a decline in the long-term productivity of the soil. 

                            EI =  R x K x LS / T

If the EI is 8 or greater, then the soil mapunit is considered to be highly erodible. This means in fact that with the worst management, this soil could lose soil at a rate eight times greater than the tolerable rate. A field that is composed of 33.33% or more HEL soil mapunits is considered highly erodible. The steeper and longer the slope length, and the lower the T value, the more likely a soil will be considered highly erodible. Generally, soil mapunits that have 0 to 3% slopes are NHEL while those with 8% or greater slope are considered HEL. Soil mapunits with slopes at 3 to 8 percent are called potentially highly erodible (PHEL) and need to have an onsite measurement of slope, or use of Geographic Information System Software that enables detailed slope calculations for a given PHEL soil mapunit in a field. In Pennsylvania, approximately 47% of soils are considered HEL while 43% are considered Potentially Highly Erodible (PHEL) and only 8.6% are considered not highly erodible (NHEL). 

Farmers don’t have to solve this problem alone as it is in all of our best interests to build soil health, maintain soil productivity, and keep soil out of our streams and waterways.  Public dollars are often targeted at highly erodible land (HEL) and in watersheds that do not have a full suite of ACT practices.  For example, using its Conservation Effects Assessment Project data, the Natural Resources Conservation Service (NRCS) focuses taxpayer-funded conservation programs in watersheds that are high priority due to the vulnerability of their soils to erosion and leaching and a lack of implemented best management practices.  Moreover, currently there are many programs to assist farmers to implement best management practices as part of climate-smart funding at the local, state, and federal levels.  For more information about NRCS programs, contact your local USDA Service Center. You can also reach out to your local county Conservation District office, your regional Pennsylvania State Conservation Commission (SCC), your local Penn State Extension office, or team members at the Center for Agricultural Conservation Assistance Training.