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PROPOSED
MEASURES: SOIL AND WATER
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Soil erosion,
because erosion has significant effects on the productivity of cropland
and on water quality. (Fig. 1)
Soil organic
matter, compaction, acidity or alkalinity, and salinity, because
these are key characteristics that determine the quality of soil for
farming. (Figs. 2, 3)
Acreage of farmland
that is irrigated or drained, because these practices are the two
most significant water management measures used to increase productivity
or make land suitable for farming. Both practices also affect water
quality. (Figs. 4, 6)
Amount of water
used per acre of irrigated land, as a measure of the efficiency
of water use. (Fig. 5)
The amount of cropland
with highly erosion-prone conditions declined by 28 million acres, from
30 percent of the Nation's croplands to 24 percent, between 1982 and
1992. During the same period, the amount of cropland with low susceptibility
to erosion increased by 31 million acres. Based on these and other factors,
USDA estimates that soil erosion was reduced substantially, although
there were probably few changes in some areas and increases in others.
Irrigated acreage
has increased by 25 percent since 1969, but almost all the increase
occurred before 1982. Irrigated acreage grew in the East and declined
in the West.
Water use per acre
of irrigated land has dropped by 25 percent since 1969, with most of
the decrease occurring between 1969 and 1990.
The amount of cropland
with drainage increased by nearly 60 percent from 1950 to 1985 (the
latest year for which data are available). Most of this increase had
occurred by 1975.
In 1996(1997, only
four states had undesirably high levels of acidity in more than half
of all soil samples tested, the same as in 1989(1990. Twenty-one states
had undesirable acidity in fewer than 25 percent of soil samples, and
many western and mountain states had high acidity in 1 percent or fewer.
However, in 10 states, the percentage of soils tested with high acidity
increased after 1990.
Change
in Land Conditions that Contribute to Erosion (1) Technical
Note
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This graph
shows the percentage of U.S. croplands that are prone to erosion.
Erosion is affected by factors such as field slope, soil type, and
rainfall, which change slowly or not at all, and by management practices
such as field terracing and amount of plant cover. These factors
combine to influence the likely amount of erosion. For example,
a soil that is naturally vulnerable to erosion can be protected
by proper management, whereas a naturally erosion-resistant soil
can erode if poorly managed. |
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Source:
The Heinz Center & USDA, Natural Resources Conservation Service
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Source:
Potash & Phosphate Institute
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STATUS
OF DATA & OTHER NOTES
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We did not
agree on a measure for reporting on soil erosion. This page reports
on soil conditions that may lead to erosion, not on erosion itself.
Information on soil conditions is available from the USDA Natural
Resources Conservation Service. No consistent national information
is available on actual soil erosion. USDA and other agencies continue
long-standing work to improve estimates of soil erosion, and these
results will be included in future reports.
No consistent
or comprehensive national information is available on soil salinity,
soil organic matter, or compaction. Information on drainage is
available only through 1985, from a one-time USDA study.
Many saline
soils have naturally high levels of salt. In addition, irrigation
in arid lands can concentrate salts in soil and water, sometimes
creating severe production and environmental problems.
Soil acidity
data are from state and private labs, compiled by the Potash and
Phosphorous Institute. This survey includes almost 2 million samples,
but the soils tested may not be representative of all soils, and
data were not available for seven states, including Alaska and
Hawaii, which are not shown on the map.
Please see
the Technical
Notes for additional information.
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