The Soils of Pennsylvania

Twelve broad soil regions can be distinguished in Pennsylvania (Figure 1.1-1). They are described in the sections that follow.

1. Eastern Lake Shore

The soils on the shores of Lake Erie developed in beach sand and lacustrine silts and clays. The soils developed in the beach sands are mostly sandy and gravelly and have rapid internal drainage, although some have a shallow water table where the silts and clays underlie the beach deposits. The landscape is mostly level, and erosion potential is therefore low. The lacustrine soils generally contain few rock fragments and have moderate root zone available water-holding capacity. This region has a mild climate due to the proximity of Lake Erie, making it suitable for the cultivation of rather unique crops such as grapes.

2. Glaciated Region of the Appalachian Plateau

The soils in northwest Pennsylvania are derived from glacial till. Glacial till is a dense material that was once under huge masses of ice (glaciers). Water percolates very slowly through the till. Many soils in this region also have a fragipan, a dense subsoil that cannot be penetrated by roots and allows very slow water and air movement. The poor drainage of many soils in this region is characterized by gleying (gray color of reduced iron) and mottling (spots of color) caused by a perched seasonal high water table and impeded percolation.

The landscape is mostly level or undulating, and erosion potential is low to moderate. Rock fragments can be present if the till is near the soil surface. The root zone available water-holding capacity of these soils is primarily determined by the depth to the impermeable layer. If the soil is shallow, crop roots will have a small volume of soil to explore for water. The result is that crops may suffer drought stress in summer on soils that are saturated in spring. Although the growing season is short, the soils in this area can be highly productive if properly drained.

3. Allegheny High Plateau

Soils in the Allegheny High Plateau of northcentral Pennsylvania developed primarily in sandstone. The dominant texture of these soils is sandy loam. They are mostly well drained. If slopes are steep, erosion potential is substantial. Rock fragment content can be high. The root zone available water-holding capacity of these soils is often low due to their coarse texture and the presence of rock fragments. The growing season in this region is short (<100 days) because of the high elevation. Due to their low agricultural productivity, most soils of the Allegheny Plateau are under forest vegetation, but there are some notable exceptions, such as potato and pasture production.

4. Glaciated Low Plateau

The soils in northeast Pennsylvania are derived from glacial till. The till in this area is typically more discontinuous than in the northwestern portion of the state. Some of these soils have a fragipan at shallow depth and therefore are somewhat poorly to poorly drained. The surface texture of these soils is predominantly silt loam. The landscape is undulating and the erosion potential is low to moderate. Rock fragments are common in the soils of this area. Some of the soils have very low root zone available water-holding capacity due to their limited rooting depth. The growing season is short due to the elevation and northern latitude.

5. Pittsburgh Plateau

The Pittsburgh Plateau in central and southwest Pennsylvania is dominated by soils developed in acid clay shales and interbedded shales and sandstones. These soils contain more clay and silt than those derived from sandstone. The surface texture of these soils is predominantly silt loam. The soils are usually well drained. The landscape of this region has rather steep slopes, and erosion is a major concern. Many of these soils also contain substantial amounts of rock fragments. The root zone available water-holding capacity of many soils in this region is moderate due to their limited depth. However, in the southwest region of this area, soils tend to be deeper and have a moderately high root zone available water-holding capacity. The growing season is rather short in most of the area, with the exception of the southwest. Agriculturally, the most productive area is located in the southwest of this region.

6. Allegheny Mountains

The Allegheny Mountain section is dominated by soils developed in sandstone. The texture is mostly sandy loam to loamy sand. Drainage is good. The landscape is often steeply sloping, and erosion potential is high. Rock fragments are common, resulting in low root zone available water-holding capacity. The high elevation of the Allegheny Mountain section gives this region a short growing season (<100 days). Much of this area is under forest vegetation, although there are some important agricultural areas.

7. Ridge and Valley Province

The ridges and valleys in the central/ eastern part of Pennsylvania are a distinct landscape characterized by sandstone ridges, shale footslopes, and shale and limestone valleys. Sandy loam soils similar to those on the Allegheny High Plateau and Allegheny Mountains sections are found on the forested ridgetops. Colluvial soils that are a mixture of sandstone and shale are found on the slopes. In the valleys, limestone-derived soils predominate, although some are shale-derived. The limestone-derived soils are among the most productive in Pennsylvania. They are usually deep, well drained, have high root zone available water-holding capacity, and have few rock fragments. The shale-derived soils are less productive because of their acidic nature, steep slopes, and generally low root zone available water-holding capacity. The soils in the valleys are on level or undulating land, and erosion potential is low to moderate. The valley soils are used intensively for agriculture.

8. Blue Ridge

The Blue Ridge province covers eastern Franklin, southern Cumberland, and western Adams Counties. The soils in this area are derived primarily from igneous and metamorphic rocks. Igneous rocks are of volcanic origin. Metamorphic rocks have been altered under great pressure below the surface of the earth. The soils in these areas are generally well drained. Their surface texture is silt loam. They often contain significant amounts of rock fragments. Steep slopes are common, giving many soils in this area high erosion potential. The root zone available water-holding capacity of the soils is commonly moderate. The high elevation results in a short growing season. Much of this area is under forest.

9.Triassic Lowlands

The soils in the Triassic Lowland section of the Piedmont developed in reddish sandstone, shale, and siltstone. The soils are generally silt loams, well drained, and located on sloping land. The erosion potential of these soils is moderate to high. The Abbottstown-Doylestown-Reading association in Bucks and Montgomery Counties is an exception to this rule. The soils in that part of this region are poorly drained and are located on level land. The soils in the Triassic Lowland section can contain substantial amounts of rock fragments. The root zone available water-holding capacity of these soils is moderate. The region has a long growing season.

10. Conestoga Valley

Limestone-derived soils predominate in the Conestoga Valley section. These soils are comparable to those in the valleys of the Ridge and Valley province. They have a silt loam surface texture and a clayey subsurface horizon. They are well drained. The landscape is level to undulating, and erosion potential is low. Rock fragments are scarce, and the root zone available waterholding capacity is high. The growing season is long. These are productive soils that are used intensively for agriculture.

11. Piedmont Upland

Soils in the Piedmont Upland section are predominantly derived from metamorphic rock. These soils have a silt loam texture, and are well drained. The landscape has rather steep slopes, and erosion potential is moderately high. Rock fragments are scarce on these soils. Their water-holding capacity is moderate to high. The growing season is long. These soils can be very productive if they are deep, and they are used intensively for agriculture.

12. Coastal Plain

The soils of the Coastal Plains section developed in coastal sands. These soils usually have a sandy surface texture and are well drained. Because the topography is level, erosion potential is typically low. The soils contain few rock fragments but have moderate root zone available water content due to the coarse soil texture. This region has the longest and warmest growing season of Pennsylvania. Most of the area is occupied by the city of Philadelphia and its suburbs.

Table 1.1-1 lists major soils of Pennsylvania, along with some of their properties and expected yield potentials.