The Extensive Margin: What Land
is Farmed?
Change in agricultural land use, including movement into and out
of agricultural production, is called change on the extensive margin
of production. That is, changes at the point or margin at which
a different land use becomes more profitable than the existing use.
Such changes reflect choices about what lands are farmed. The term
"margin" should not be confused with "marginal"
soils or "marginal" land from an environmental viewpoint.
For example, changes from cropland to urban uses, and changes in
the type of agricultural production, such as changes from pasture
and rangeland to cropland, are extensive margin changes. Changing
land use from cropland to urban uses reveals a great deal about
the relative economic returns from those uses, and will have different
impacts on the environment than changing from cropland to forest
use.
Trends in the extensive margin of land use are revealed in two
important data sets:
-
Major Uses of Land (MLU),
compiled by ERS, has provided land use data every 5 years
since 1945. Major Uses of
Land in the United States, 2002, the latest report,
presents data for all 50 States and includes Federal land
uses. A detailed
database providing all data since 1945 is available on
this website.
-
The National
Resources Inventory (NRI), conducted every 5 years by the
Natural Resources Conservation Service, provides land use data
that show the source and eventual use of each change
in land use between two periods, as well as the acres of land
that remain in the same use. The NRI provides consistent land
use data for four dates (1982, 1987, 1992, and 1997) for 49
States (Alaska is excluded), for all non-Federal lands. NRI
data are summarized in an NRCS
report.
Sources of Land Converted to Agriculture
Contrary to popular belief, land continues to be converted from
less intensive uses, like forest and rangeland, to agricultural
uses, like cropland and pasture. Shifts in the other direction also
occur in different regions and over time.
What use did the land come from that is now used for
agriculture? Forest land contributed 8.3 million acres (55 percent)
of the land that shifted into agriculture from 1982 to 1997.
Of the total land converted from forest land between
1982 and 1997, more than three-fourths went to pastureland and rangeland.
Of total land shifting out of agriculture, 22.7 million acres (46
percent) shifted into forest use, 14 million acres of which was
former pastureland.
Sources of land use shifting
into and out of agriculture, 1982 to 1997 |
Land use |
Non-agricultural shifts to agriculture |
Agricultural shifts to non-agricultural
uses |
Net land use shifts |
|
1,000 acres |
Forest land |
8,304 |
22,720 |
-14,416 |
Minor land |
3,120 |
6,481 |
-3,361 |
Urban and built-up land |
3 |
13,924 |
-13,921 |
Rural transportation |
383 |
685 |
-302 |
Water areas |
654 |
1,500 |
-846 |
Federal land 1 |
2,685 |
4,101 |
-1,416 |
Total |
15,148 |
49,410 |
-34,262 |
1/ "Federal
land" is not a land use. While the NRI shows Federal land,
it does not account for land use change on Federal land.
Source: ERS-USDA, based on NRI data. |
Much of the shift from pastureland to forest use is due to reclassification
over time. As trees grow, they expand to reach the 10-percent canopy
cover used to define forest land, which changes the pastureland
classification to forest use.
Even though now classified as forest, the land may still be used
for grazing. Shifts between grazing land and forest uses are common
and though technically considered shifts into and out of agriculture,
they really represent multiple, overlapping uses.
Agricultural Land Converted to
New Uses
Most land shifting from agriculture to another use between 1982
and 1997 went into forest use: 22.7 million acres (46 percent) of
the land shifting out of agriculture was reforested.
Land shifting into urban uses seldom shifts back. In 15 years,
only 3,000 acres shifted from urban into agricultural uses, whereas
13.9 million acres (28 percent) shifted from agricultural to urban
uses.
Federal land in the NRI is an ambiguity since the NRI does not
inventory land use on Federal lands. The NRI shows the acres of
land that convert to Federal ownership, and visa versa. But the
land usemostly rangeland and forest landon Federal land
is not collected in the NRI, nor are land use shifts.
Changes in Agricultural Land
Use
At the national level, cropland used for crops decreased about
34 million acres between 1982 and 1997, or about 9 percent. Some
of this cropland went into the Conservation Reserve Program, and
some was idled or used for pasture. Grassland pasture and range
decreased 16.5 million acres over this period, or 3 percent. Overall,
agricultural land use decreased about 3 percent since 1982.
Changes in agricultural uses of
land, 1982 to 1997 1 |
Agricultural land
use |
1982 |
1997 |
Difference
1982-97
|
|
1,000 acres
|
Percent |
Cropland used for crops 2 |
382,755 |
348,701 |
-34,054 |
-8.9 |
Idle cropland |
21,498 |
6,046 |
-15,452 |
-71.9 |
Conservation Reserve 3
|
0 |
32,793 |
32,793 |
0
|
Cropland used only for pasture |
65,033 |
67,512 |
2,479 |
3.8 |
Grassland pasture and range
4 |
596,664 |
580,165 |
-16,499 |
-2.8 |
Total |
1,065,950 |
1,035,217 |
-30,733 |
-2.9 |
1/ Includes Alaska.
2/ Cropland harvested, crop failure, and cultivated summer fallow.
3/ From Farm Service Agency, USDA.
4/ Includes Federal rangeland grazed.
Source: ERS-USDA, Major Land Uses data product. |
Both Major Land Use data and
the NRI data show decreases in agricultural
land of about 30-34 million acres from 1982 to 1997. However,
the decreases differed in magnitude by region. The Major Land Use
data, which is a longer data series, show different trends for earlier
years. In addition, cropland and grazing land did not always both
change in like proportions, or even in the same direction.
While the national trend in cropland has been fairly constant, some regional
trends have not. Cropland in the Northeast
region has decreased dramatically since 1945, while cropland
in the Mountain region has increased.
Urban pressures and a comparative disadvantage in many crops have
resulted in the conversion of Northeast cropland to other uses.
Conversions from grassland,
pasture, and range have primarily accounted for the increase
in cropland in the Mountain region. Overall,
the Eastern United States has tended to lose cropland, while the
Western United States has tended to gain cropland.
The above results are by Farm Production Regions. Trends can also
be shown for the ERS Farm Resource Regions using NRI data. The NRI,
a shorter series starting in 1982, shows that cropland
decreased in all Farm
Resource Regions but two, the Heartland and the Northern Great
Plains. These two regions also show a decrease in cropland if CRP
is accounted for separately. Here, CRP is included as idle cropland.
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