NRI Information

History of the NRI

  • In 1934, the Soil Erosion Service (SES) conducted the soil erosion inventory.
  • In 1942, the Soil Conservation Service (SCS) analyzed the census of agriculture to produce Soil and Water Conservation Needs Estimates of the United States by states.
  • In 1958, the SCS, with other USDA agencies, produced the Conservation Needs Inventory based on land use, soil and water conservation, and management of land resources.
  • In 1967, the SCS updated the 1958 inventory - this time with specific sample points.
  • The beginning of the modern NRI began in 1977 with the Soil and Water Resources Conservation Act which started the monitoring of soil, water and related resources on non-federal lands and to create a report on the findings.
  • In 1982, the NRI focused mainly of highly erodible land and served as the locational basis of all future NRIs (PSU and point locations). The NRI of 1987 was based on a subset of the those locational points while in 1992 and 1997 the sampling set was increased considerably and was only slightly less than that of 1982. 

Maryland NRI

The National Resources Inventory (NRI) is a compilation of natural resources for non-federal land. In 1977, the NRI monitored soil erosion and conservation practices. In 1982, the NRI became more comprehensive and formed the basis for future inventories which have been repeated every 5 years - including the 1997 NRI. This repetition provided historical data needed to produce land use trends. Future inventories will be continuous with land use data collected annually. Depending if a land use/coverage is common or rare, NRI results may be misleading at the county level. Statistical reliability increases if the analysis is taken at state or sub-state sampling (i.e. major land use area or hydrological unit areas).

The national inventory is based on primary sampling units (PSUs). In Maryland, the rectangular PSUs are approximately 109 acres in size and, on average, contain three sampling points. Both area and point measurements of land use and cover are collected within the PSUs. With federal lands excluded, private, municipal, county, and state land, as well as water bodies that fall inside a PSU are sampled in Maryland. Within the PSU, area measurements may include urban land, farmsteads, rural transportation features and perennial water areas such as streams, ponds and lakes. Point determinations are mainly qualitative and may involve the following: land ownership, enrollment in the conservation reserve program, primary land use, soil information, irrigation use, agricultural erosion, wetland status, and conservation practices installed.

1997 NRI Highlights

  • Maryland has a total of 7,869,900 acres of land statewide. During the 1997 inventory, 6,116,200 acres were reported as private, municipal, county or state owned, 168,900 acres were in federal hands while an 1,584,800 acres was water.
  • Forest areas decreased approximately 85,000 acres or about 3.5 percent in Maryland between 1982 and 1997. Of the 85,000 acres, 34,000 acres were lost between 1992 and 1997. Oak-Hickory was the dominant association in areas west of the Chesapeake Bay, while Oak-Pine and Oak-Gum-Cypress became prominent for areas east of the Bay.
  • Cropland decreased around 178,300 acres or about 10 percent for Maryland between 1982 and 1997. Of the 178,300 acres, 56,700 acres were lost between 1992 and 1997. The greatest loss came to metropolitan counties surrounding Washington, D.C. and Baltimore City. Pasture acreage decreased 66,000 acres or 12 percent statewide between 1982 and 1997.
  • Urban land increased nearly 316,500 acres or an increase of 38 percent for Maryland between 1982 and 1997. Of the 316,500 acres, 176,100 acres of land became urbanized between 1992 and 1997. For the change between 1982 and 1997, 141,800 acres came from forested areas, 110,700 acres from cropland, 59,000 acres from pasture and the remaining from miscellaneous sources. Metropolitan counties surrounding Washington, D.C. and Baltimore City had the greatest percentage of land urbanized. Adjacent counties to the metropolitan counties had the largest increase.
  • Prime farmland consisted of 1,133,400 acres. Out of the state’s 6,116,200 acres of non-federal land, this was approximately 19 % of the total. Areas with prime farmland centered around two regions: the Eastern Shore from Talbot to Cecil counties and north central Maryland from Carroll to Washington counties.

Urban Trends

Maryland is located on the densely populated eastern seaboard of the United States that extends from southern Maine to northern Virginia. This area is rapidly growing and from 1982 to 1997 Maryland, alone, developed 316,500 acres of land. In all, Maryland has 1,145,600 acres of urban land (19 percent of total non-federal land), making it the sixth most urbanized state in the country. In 1997, the counties that had the highest percentage and greatest acreage of urban land were within the Baltimore-Washington-Annapolis population triangle. They included Montgomery and Prince George’s Counties, which surround Washington D.C., and Baltimore and Anne Arundel Counties, which surround Baltimore City. Howard County, which is shared by both the Washington, D.C. and Baltimore City metropolitan areas, is the most urbanized county in Maryland. It had approximately 44 percent of its land developed.

Likewise, Maryland is least built-up at its fringes. One periphery area is the Eastern Shore of Maryland - the part of Maryland east of the Chesapeake Bay. The most rural counties for this region are Somerset, Dorchester, and Kent Counties. Another periphery area is situated in western Maryland and includes Garrett, Allegany, and Washington counties. Population density for western Maryland decreases the further west traveled. The other sparsely populated section of Maryland is southern Maryland. This includes St. Mary’s, Charles and Calvert counties. In Southern Maryland, the population density decreases the further south traveled.

The areas that had the highest growth rate within the 1982 to 1997 time span indicate that the population is expanding from the Baltimore-Washington-Annapolis urban core to outlying counties. Two southern Maryland counties near Washington D.C. - Calvert and St. Mary’s Counties - showed hefty growth rates of 148 and 63 percent respectively. Urban growth in Frederick County, northwest of Washington, D.C. increased 76 percent, Carroll County, west of Baltimore City, increased 63 percent, and Cecil County, in the direct line of the Boston-Washington urban axis, increased 79%. How fast a county is urbanizing can be measured a couple of ways. One way is the percent increase of county of a period of time and is based on the initial acres of urban land. The counties that had a large percent increase had been relatively rural counties in 1982. However, counties with a large urban base in 1982 - Montgomery, Prince George’s, and Baltimore counties - had a relatively low rate of growth. But these counties still had the largest total amount of land urbanized in 1997.

Crop and Pasture Trends

The amount of land in crop production for Maryland decreased a total of 178,300 acres, down from 1,794,700 acres in 1982 to 1,616,000 acres in 1997. Crop loss occurred in nearly every county. The greatest loss happened in counties along the Pennsylvania Border or in counties around the Washington D.C. metropolitan area. With the exception of Queen Anne’s County, crop loss was less pronounced for the Eastern Shore counties than in other parts of the state. In 1997, the counties with the largest amount of land in crops were either on the Eastern Shore (Queen Anne’s, Caroline, Kent, Dorchester, and Talbot counties) or in west central Maryland (Frederick, Carroll, and Washington counties).

Maryland produces a variety of crops, including corn, soybeans, small grains and tobacco. Small grains such as wheat is grown mainly in Eastern Shore counties while oats is almost exclusive to Garrett county in far western Maryland. Barley is grown both on the Eastern Shore and in the Mason-Dixon region. Regions growing corn is evenly split between the Mason-Dixon counties (chiefly Frederick County) and Eastern Shore counties (especially Kent County). However, the Eastern Shore (particularly Queen Anne’s County) dominates soybean acreage. Land seeded to Tobacco, is entirely in southern Maryland. Overall, Maryland has not historically relied on irrigation for crop production. One exception to the trend is the use of irrigation for grain crops in the central part of the Eastern Shore with Caroline County as the epicenter.

Whether land is in crop, hay or pasture production and depending on the topography, the erosion rates will differ in the various regions of Maryland. A field is determined to be highly erodible by calculating the erosion rate using the Universal Soil Loss Equation (USLE). A conservationist will use the USLE equation to determine the soil loss (T) in tons per acre per year by multiplying the following factors: the rainfall constant for an area (R), the inherent erodibility of a soil (K), the percent slope of a field (S), the length of that slope (L), the crop cover (C), and the conservation practices used by a farmer (P). At a loss greater than 3 to 5 tons per acre, a field is losing soil faster than it is creating soil. Comparing erosion rates for agricultural land, using 8-digit watersheds as our geographic unit, we can see that the Patuxent, Gunpowder-Patapsco, and Lower Susquehanna Watersheds had the highest amount or agricultural land with a T of greater than 6. Conversely, the Youghiogheny, Pocomoke, Nanticoke, and the Blackwater-Wicomico waterhseds had the most agricultural land with a T less than 3 tons per acre per year. The Patuxent, Gunpowder-Patapsco watersheds are in the very hilly terrain of Southern Maryland or Mason-Dixon Region. Additionally, the highly erodible watersheds have a large percentage of land in annually tilled crops. The Youghigheny watershed, in far Western Maryland, is hilly but has a majority of the land cover permanently seeded to grass as hay or pastureland. On the other hand, the majority of the agricultural land in the Pocomoke, Nanticoke, and the Blackwater-Wicomico waterhseds are in annually tilled crop production, but that the following wathersheds are in the very flat topography of the lower Eastern Shore.

With the exception of a few counties on the Eastern Shore and in Southern Maryland, Maryland had a net decrease for land in pasture between 1982 and 1997. In 1997 Maryland had 478,000 acres of pasture compared to 544,600 acres in 1982, producing an overall decrease of 66,000 acres. Areas with the greatest loss were either in western counties that run along the Pennsylvania border or in counties that surround the Washington D.C. Metropolitan region. Ironically, it is in the counties along the Pennsylvania border, which still contain the greatest amount and the highest percentage of land in pasture.

Forest Trends

In 1997, western Maryland had the highest percentage of land in forest. Between 1982 and 1997, the change in forest acres had a net decrease of 116,400 acres statewide. Only in the four western Maryland counties of Garrett, Allegany, Washington and Frederick counties and the two central Eastern Shore counties of Talbot and Caroline were there an increase in forest land. Counties that had the greatest loss of acres were in the Maryland metropolitan areas: Prince Georges, Montgomery, Anne Arundel, Howard and Baltimore counties. Most of this loss was due to rapid urbanization.

Although Maryland is a small state, it is quite varied in its topography, climate and vegetation. Within the state’s borders lay seven distinct physiographic or Major Land Resource Areas (MLRAs). They include from West to East, the Eastern Allegheny Plateau and Mountains, the Northern Appalachian Ridges and Valleys, the Blue Ridge, the Northern Piedmont, the Northern Coastal Plain, the Mid-Atlantic Coastal Plain, and the Northern Tidewater Region. Between these physigraphic regions are changes in vegetation; one type of variation in vegetation relates to the major forest groupings.

Looking at forest composition based on Major Land Resource Areas (MLRAs), Oak-Hickory tends to be the dominant forest group state-wide. It makes up the majority of forest types in the regions that runs along the Pennsylvania border, including the Eastern Allegheny, the Blue Ridge, the Northern Appalachians, the Northern Piedmont, and the Northern Coastal Plain. Only in the extreme western region of the Eastern Allegheny with its cooler climate does the Maple-Beech-Birch group constitute a significant percentage of the forest canopy. Traveling from the Mason-Dixon counties to the warmer and more poorly drained Eastern Shore, the forest composition again changes as the dominance of Oak-Hickory wanes. In the Mid-Atlantic Coastal Plain and Northern Tidewater resource areas, Oak-Pine ranges from approximately one-third to one-half of the forest composition. These two areas also include large percentages of Loblolly-Shortleaf Pine and Oak-Gum-Cypress. In fact, in the Northern Tidewater resource area, the Oak-Gum-Cypress and Loblolly-Shortleaf Pine associations each form almost a quarter of the overall canopy.

Prime Farmland

Prime Farmland, as defined by the U.S. Department of Agriculture, is the land best suited to food, feed, forage, fiber, and oilseed crops. It may be cultivated land, pasture, woodland, or other land, but it is not urban land or water areas. It has soil qualities, favorable growing season, and ample moisture supply – either natural or with irrigation - needed to produce sustained high yields on well-cultivated fields. Production takes comparatively minimal economic and energy inputs and produces minimal environmental damage. Prime soils have the following inherent characteristics: a minimum amount of surface rocks, low susceptibility to erosion and have not had been excessively eroded in the past, a favorable pH, an acceptable level of content of salt and sodium, water and air permeability, and are not subject to prolonged saturation. They also have the following related qualities: have nearly level to gently sloping topography, and rarely or never flood during the growing season.

Maryland, on average, has a little over 23 percent of its soils as prime, excluding federal land, urban land and water areas. Crop production, either cultivated or uncultivated, consists of 47 % prime soils. Land enrolled in the conservation reserve program (CRP), however, has the highest percentage of its land as prime soils. Approximately 57% of total CRP land are made up of prime soils. Although forestland is only second to cropland in the total acres of prime soils statewide, the percentage of prime soils is only about 9 percent.

Regionally, the Eastern Shore and the Mason-Dixon Counties have a higher than average percentage of prime soil (approximately 28 and 31% respectively). Counties with the highest amount of prime farmland are found either in the upper part of the Eastern Shore, including Kent, Caroline, Queen Anne’s and Talbot counties or along the Pennsylvania border such as Washington, Carroll and Cecil counties. Southern Maryland has about 18 percent of its soil as prime while fewer than 2 percent of Western Maryland soils are prime. As expected, individual counties with least amount of Prime soils tend to be in Southern or Western Maryland and include Garrett, Allegany, Calvert, and Charles counties.

Land Capability Classification*

Land capability classification is used in the soil survey to group mapping units that require similar management, treatment needs, and have limitations for agricultural production. The soils with the same capability unit, if used for crop production, should have comparable yields for similar crops and need the same input of management. The nomenclature of the capability class uses a Roman Numeral to describe the overall limitations and has a lower case letter following it to describe its capability sub-class. The larger the Roman Numeral, the more limitation the land has for agricultural production and the more intensive the need for management practices that produce yields and prevent soil degradation such as erosion. For instance, a capability class represented by "I" would have no limitations, while a class of "VI" would have severe limitations for cultivation. Classes I to IV are suited to production of crops and forages, with II through IV needing increased conservation needs. Class I soils are generally deep well drained, easily worked, and have little susceptibility to erosion. Classes II through IV have increasing limitations such as slope, poor drainage, risk of erosion or extensive past erosion, slow permeability, shallow depth to bedrock, and/or low moisture holding capacity. With extensive conservation practices and structures, classes V and VI could be brought into agricultural production but are much better suited for planting of permanent pasture or trees. Classes VII and VIII have limitations so severe, that it is impractical to bring them into any type of production and would be best used for wildlife management or recreation. 

Although the Eastern Shore had the highest percentage of class I soils at 6 percent, the Mason-Dixon region had the greatest combined amount of classes II and III – 61 percent. Southern Maryland had 54 percent of its land in classes II and III. The region with soils having the most limitations is Western Maryland. This region had 71 percent of its land classes VI and VII.

There are three main sub-capability classes in Maryland: s (soils that are shallow or droughty), e (soils susceptible to erosion), and w (soils with wetness limitations). The regional topography seems to determine the dominant sub-class limitation. In Western Maryland with its mountainous terrain and steep topography, shallow soils with root zone problem (s) are the dominant limitation followed by erodible soil (e). In the dissected area of central Maryland (Mason-Dixon and southern Maryland counties), the biggest limitation for soils is by far their susceptibility to erosion (e). On the Eastern Shore of Maryland with its nearly level topography and high water table, the majority of soils are limited by wetness (w).

* Land Capability Classification. Agriculture Handbook No. 210. Soil Conservation Service. U.S. Department of Agriculture. Issued September. 1961. Reprinted January, 1973


Dean Cowherd
State Soil Scientist (acting)
Phone: 443-482-2931