Modern Agriculture: Environmental Effects
CORNELL COOPERATIVE EXTENSION
Modern Agriculture: Its Effects on the Environment
Nancy M. Trautmann
Keith S. Porter
Center for Environmental Research
Robert J. Wagenet
Dept. of Agronomy
Agriculture has been a major component of the United States economy ever since
colonial days, when 9 out of 10 working persons were employed on a farm.
Produclivity of American agriculture has tripled since then, and today only 3
percent of our labor force produces enough food and fiber to meet domestic needs
as well as supplying about 10 percent of total overseas consumption. This huge
increase in efficiency has been the result of many factors, including use of
fertilizer, and pesticides, introduction of farm machinery, development of
hybrid strains, and increased knowledge about farm management practices. As
agriculture has become more intensive, farmers have become capable of producing
higher yields using less labor and less land. Intensification of agriculture has
not, however, been an unmixed blessing. Environmental impacts have increased,
including potential degradation of the soil and water resources vital to both
farm productivity and human health. Such environmental problems can best be
understood by tracing their evolution through the history of farming in this
Agriculture in the United States dates back to the food-raising activities of
American Indians, and over half of the value of our current crops comes from
plants such as corn, cotton, potatoes, and tobacco that were first domesticated
by Indians in South and North America. In the early 1600s when the colonists
were making their way to America, agricultural methods in England and other
parts of the world were still primitive. Fields were dug by oxen pulling wooden
plows, seeds were broadcast by hand, and grains were harvested with scythes just
as they had been for the previous 2,000 years. From the Indians the first
American settlers learned how to clear land, till the fields, and grow the corn
that was crucial to their initial survival.
Although Indians taught the colonists to plant fish with their corn,
fertilization of other crops was not a common practice. The native fertility of
the relatively acid and nutrient-poor eastern soils was rapidly exhausted, and
pioneering families commonly abandoned their farms and moved on to homestead the
still fertile virgin lands to the west. By 1850 one traveller wrote, "Eastern
Virginia appeared to have suffered the ravages of a great war or an attack by
another horseman of the Apocalypse. I traveled for 50 miles on horseback and
could find nothing but abandoned farms and plantations with buildings in decay
and fields overgrown with nettles and brush. Mother Nature is reclaiming that
which for 200 years has been giving food and clothing to man."
Agricultural Revolution. The mid-1800s began an era of great change in American
agriculture, influenced by the British agricultural revolution, which brought
advances in cultivation methods, breeding of improved crop varieties, and use of
fertilizers and crop rotations to maintain soil productivity. Crop fertilization
was introduced to the American colonies in the 1850s when ships were used to
import guano, the droppings from seabirds living on islands off the coast of
Peru. A vigorous market soon developed for soil amendments such as guano,
manure, crushed bone, and lime; and by 1860 seven factories had been established
in the United States to manufacture mixed chemical fertilizers.
The use of pesticides also began in the mid 1800s, when it was discovered that
dusting of grape plants with sulfur provided a cure for powdery mildew. Soon
afterwards, an arsenic-containing compound called Paris green was introduced for
control of the Colorado potato beetle, an insect native to the eastern slopes of
the Rocky Mountains, which became a serious agricultural pest because of its
appetite for domestic potatoes grown by pioneers. Chemical control of
agricultural pests expanded rapidly after these initial discoveries, and by 1893
there were 42 patented insecticides offered by several manufacturers.
The benefits of irrigation were discovered in the 1840s, when Mormons in Utah
softened their crusty soils by damming a creek, and prospectors in California
discovered that water diverted to gold mining sluices produced lush plant growth
in the desert. Congress passed several laws in the next few decades to assist
western states in developing extensive and costly irrigation systems.
Farm labor requirements diminished with the introduction of mechanization.
Invention of machines for tilling, planting, reaping, and threshing vastly
increased farm efficiency in the mid 1800s. The internal combustion engine was
invented in Europe in the late 1800s, and in 1892 the first successful
gasoline-powered tractor was introduced in Iowa. By the early 1900s tractors
that were small enough and cheap enough to interest the average farmer and could
do the work of 17 men and 50 horses were being produced. Tractors gradually
became popular, although it was not until 1953 that there were more tractors
than horses on U.S. farms.
Ever since colonial days, agricultural leaders have been interested in
increasing the productivity of American farming. George Washington and Thomas
Jefferson were leading agricultural reformers in the late eighteenth century,
experimenting with crop rotation, manure applications, new crops, and improved
livestock. In 1862 President Lincoln signed legislation creating the U.S.
Department of Agriculture and granting public land to the states for
establishment of agricultural colleges. Federal support for state agricultural
experiment stations began in 1887, providing the basis for scientific
improvement of American agriculture. As land became less available for
settlement in the West, people became more interested in maintaining soil
fertility and increasing crop yields on their existing farms. In 1914 Congress
responded to this need by providing funds for state agricultural extension
programs assist farmers in adopting improved farming methods.
Conservation Beginnings. The unprecedented damage to farmland caused by the dust
bowl storms of the 1930s focused national attention on the need for soil and
water conservation measures to maintain farm productivity. Before settlement the
Great Plains had consisted of vast acreages of grasslands roamed by wandering
herds of bison and antelopes. The grasses were adapted to cycles of moisture and
drought, and their dense root systems held the powdery soils in place against
the strong prairie winds. The Homestead Act signed by President Lincoln in 1862
offered free land to anyone willing to cultivate it for 5 years, but it was not
until production of the steel plow in the late 1800s that widespread cultivation
became possible on the dense sods of the plains. The rich soils produced
bountiful crops, and between 1870 and 1910 the population of seven plains states
increased by a factor of 10, faster than any other section of the country at any
time. In the 1930s, however, disaster struck. Several years of severe drought
caused crop failures leaving the light-textured, powdery soils unprotected
against the strong prairie winds. Millions of tons of rich topsoils were lost in
dust storms so severe that they caused virtual blackouts in the middle of the
day and left houses, roads, and fields buried by dust and sand. Skies were
blackened as far east as New York City, and even ships 300 miles out in the
Atlantic Ocean reported dust accumulations on board.
In response to the urgent need for soil and water conservation programs to halt
farmland destruction, the Soil Conservation Service was established in 1935. SCS
employees set up demonstration plots and taught methods such as contour plowing,
terracing, and strip-cropping to retain water on the fields and reduce runoff
and erosion. Windbreaks were planted to break the force of the prairie winds,
tillage methods were changed to reduce exposed soils, and vegetation or stubble
was retained on the fields after the growing season to provide protective cover.
With these methods, damaged lands were reclaimed and the dust storms were
brought under control.
Intensification of Agriculture. Productivity of U.S. agriculture increased
gradually until World War II when the additional demands for food led to rapid
changes in farming methods. The war economy stimulated the conversion from
animal to mechanical power, resulting in increased output per worker. Use of
fertilizer increased by 50 percent between 1940 and 1944, resulting in greater
crop returns. The discovery of DDT and other synthetic organic pesticides vastly
increased pest control capabilities and made it possible to increase efficiency
through practices such as continuous cropping and devoting large acreages to a
In the 25-year period between 1950 and 1975, agricultural productivity changed
more rapidly than at any other time in American history (fig. 1. See fact
sheet). Although the acreage in farming dropped by 6 percent and the hours of
farm labor decreased by 60 percent, farm production per hour of on-farm labor
practically tripled, and total farm output increased by more than half. These
dramatic changes were produced by technological innovations, development of
hybrid strains and other genetic improvements, and a fourfold increase in the
use of pesticides and fertilizers (fig. 2. See fact sheet).
The result of all these changes has been that agriculture has become more
intensive, producing higher yields per acre by relying on greater chemicals use
and technological inputs. It also has become more expensive, relying on purchase
of machinery and chemicals to replace the heavy labor rcquirements of the past.
To remain competitive, farmers have been forced to become more efficient,
farming ever larger acreages with bigger equipment and more fertilizers and
pesticides. Small farms growing a wide variety of crops have in large part been
replaced by much larger farms consisting of extensive fields of a single crop.
As a result, the number of farms has dropped by half since 1950, and average
farm size has doubled (fig. 3. See fact sheet). Today only 2 percent of U.S.
farms produce 70 percent of the vegetables, 50 percent of the fruit and nuts,
and 35 percent of the poultry products grown in this country.
Although the intensification of agriculture has vastly increased productivity,
it also has had a number of potentially detrimental environmental consequences,
ranging from rapid erosion of fertile topsoils to contamination of drinking
water supplies by the chemicals used to enhance farmland productivity.
Impacts of Intensive Farming on Soil and Water Resources
Damage to Soil. Soil erosion from farmland threatens the productivity of
agricultural fields and causes a number of problems elsewhere in the
environment. An average of 10 times as much soil erodes from American
agricultural fields as is replaced by natural soil formation processes. Because
it takes up to 300 years for 1 inch of agricultural topsoil to form, soil that
is lost is essentially irreplaceable. The consequences for long-term crop yields
have not been adequately quantified. The amount of erosion varies considerably
from one field to another, depending on soil type, slope of the field, drainage
patterns, and crop management practices; and the effects of the erosion vary
also. Areas with deep organic loams are better able to sustain erosion without
loss of productivity than are areas where topsoils are shallower.
Erosion affects productivity because it removes the surface soils, containing
most of the organic matter, plant nutrients, and fine soil particles, which help
to retain water and nutrients in the root zone where they are available to
plants. The subsoils that remain tend to be less fertile, less absorbent, and
less able to retain pesticides, fertilizers, and other plant nutrients. Why then
is erosion allowed to continue at excessive levels on many U.S. farms? Often the
short-term costs of implementing erosion control measures far exceed the
immediate economic benefit to the farmer, but such cost-benefit analyses fail to
take into account the long-term losses of fertility and water-holding capacity
of the soil. Up to a certain point, increased fertilization and irrigation will
compensate for the lower soil fertility. Long-term loss of farmland productivity
and damage to the environment from eroded sediments, therefore, often are
overlooked in the need for short-term economic gains.
Over the past 50 years, the negative effects of soil erosion on farm
productivity have been masked by improved technology and increasing use of
fertilizers and pesticides. Ironically, many of these measures used to increase
the short-term productivity of American farms are also causing excessive
erosion, which threatens productivity over the long term. For example,
diminished use of cover crops leaves soils unprotected from wind and rain during
much of the year, and increased mechanization has led to use of larger fields
without windbreaks or drainage contours.
The effects of erosion are also felt elsewhere in the environment. A recent
study estimated the off-site cost of cropland erosion in the United States to be
in the range of a billion dollars per year (Clark, Haverkamp, and Chapman 1985).
Eroded soil clogs streams, rivers, lakes, and reservoirs, resulting in increased
flooding, decreased reservoir capacity, and destruction of habitats for many
species of fish and other aquatic life. The eroded soils contain nutrients and
other chemicals that are beneficial on farm fields, but can impair water quality
when carried away by erosion. As a result, drinking water supplies may contain
nitrate or organic chemicals in concentrations that exceed public health
standards, or surface waters may become clogged with excessive plant growth from
the added nutrients.
In recent years American farmers have increasingly adopted conservation tillage
as a method of cutting soil and water losses by leaving a protective crop
residue on the soil surface. This residue protects the soil from wind and rain
and can greatly reduce cropland erosion. One drawback to conservation tillage,
however, is that weed control is accomplished using chemical herbicides rather
than physical cultivation. These chemicals reduce the populations of beneficial
insect and animal species, and in some areas they contaminate water supplies.
Surface runoff carries herbicides to streams and lakes, and groundwater can
become contaminated by percolation of water and dissolved chemicals downward
through the soil. Eight different herbicides have been detected in groundwater
in at least 18 states, and others have been found in more limited ranges.
Methods need to be developed for combining the soil- saving aspects of
conservation tillage with less chemically intensive means of weed control.
Even when soil erosion is not excessive, intensive agriculture can impair soil
quality by depleting the natural supplies of trace elements and organic matter.
In natural ecosystems, soil fertility is maintained by the diverse contributions
and recycling of nutrients by a wide range of plant and animal species. When
this diversity is replaced by a single species grown year after year, some trace
elements are depleted if not replaced by fertilization. The organic content of
the soil also diminishes unless crop residues or other organic materials are
supplied in sufficient quantities to replace that consumed over time.
Contamination of Water. In the Northeast water supplies are generally plentiful,
but are increasingly becoming threatened by contamination. Farming is one
potential source of such contamination. Surface runoff carries manure,
fertilizers, and pesticides into streams, lakes, and reservoirs, in some cases
causing unacceptable levels of bacteria, nutrients, or synthetic organic
compounds. Similarly, water percolating downward through farm fields carries
with it dissolved chemicals, which can include nitrate fertilizers and soluble
pesticides. In sufficient quantities these can contaminate groundwater supplies.
Fertilizers. Nutrients are lost from agricultural fields through runoff,
drainage, or attachment to eroded soil particles. The amounts lost depend on the
soil type and organic matter content, the climate, slope of the land, and depth
to groundwater, as well as on the amount and.type of fertilizer and irrigation
The three major nutrients in fertilizers are nitrogen, phosphorus, and
potassium. Of these, nitrogen is the most readily lost because of its high
solubility in the nitrate form. Leaching of nitrate from agricultural fields can
elevate concentrations in underlying groundwater to levels unacceptable for
drinking water quality. In the Suffolk County area of Long Island, for example,
almost 10 percent of private wells tested for nitrate exceed the 10 mg/l
drinking water standard.
Phosphorus does not leach as readily as nitrate because it is more tightly bound
to soil particles. However, it is carried with eroded soils into surface water
bodies, where it may cause excessive growth of aquatic plants. If this process
proceeds far enough, lakes and reservoirs become choked with decaying mats of
algae, which have offensive odors and can cause fish kills from the resulting
lack of dissolved oxygen.
Potassium, the third major nutrient in fertilizers, does not cause water quality
problems because it is not hazardous in drinking water and is not a limiting
nutrient for growth of aquatic plants. It is tightly held by soil particles and
so can be removed from fields by erosion, but generally not by leaching.
Pesticides. The trend toward intensive crop production in modern farming has led
to increased potential for damage by pests and diseases. Predators that would be
present in a mixed biological community are not supported by large fields of a
single crop; so farmers, instead, rely on chemical measures for crop protection.
Use of pesticides on U.S. farms has risen 1O-fold over the past 40 years as
agriculture has become more intensive. One drawback to this is that pesticides
generally kill not only the pest of concern, but also a wide range of other
organisms, including beneficial insects and other pest predators. Once the
effect of the pesticide wears off, the pest species is likely to recover more
rapidly than its predators because of differences in the available food supply.
Previously unimportant species may also become significant crop pests when their
natural predators are killed by pesticide applications.
Another drawback to the increasing pesticide use is the development of
resistance in pest species. The individual pests that survive pesticide
applications continue to breed, gradually producing a population with greater
tolerance to the chemicals applied. Presticides, therefore, have to be used in
ever increasing quantities or replaced with new chemicals to adequately control
Following World War II, DDT and related chlorinated hydrocarbons were introduced
as potent new pesticides and were used throughout the world for protection of
agricultural crops, as well as control of mosquitoes, lice, and other human
pests. In 1962 Rachel Carson's book Silent Spring brought public attention to
the fact that these organic compounds are highly persistent in the environment
and accumulate in animal tissues, causing water contamination, fish kills, and
decline of some bird populations. DDT was banned for agricultural use in the
United States in 1973, and since that time it and similar chlorinated
hydrocarbons have been replaced by less persistent, but more acutely toxic,
compounds. Because some of these new pesticides are highly soluble in water,
they may leach to groundwater underlying farming regions. In Suffolk County at
the eastern end of Long Island, for example, 13 different pesticides have been
measured at least once in groundwater samples. Twelve percent of the wells
tested in Suffolk County have exceeded the drinking water guideline for
aldicarb, a highly soluble pesticide used from 1975 to 1979 to control thc
Colorado potato beetle. Nationwide sampling for pesticides has been quite
limited, but 23 states have reported at least one of 22 pesticides in
In the past couple of decades, awareness has been growing of the many potential
problems caused by the heavy use of chemicals in modern agriculture. This,
combined with the rapid rise in the cost of fertilizers and pesticides, has led
many farmers to seek ways of reducing their reliance on chemical- intensive
methods of farming. A small but growing percentage of farmers are farming with
no synthetic chemicals, and many others are reducing their overall chemical use.
Agriculture research has begun to focus on ways of maintaining environmental
quality while producing acceptable crop yields. One example is integrated pest
management, aimed at controlling pests through a combination of methods that
minimize undesirable ecological effects. Continuing research and education need
to be conducted on farming practices that produce profitable yields while
maintaining environmental quality and the long-term productivity of the land.
Agriculture in the United States has changed greatly in the past few decades.
During the 1950s and 1960s American farmers depended on cheap energy, plentiful
water supplies, and extensive use of chemical fertilizers and pesticides to
produce high yields with decreasing labor on reduced amounts of land. In recent
years the costs for fuel and chemicals have increased sharply, the high use of
pesticides has led to development of resistance in many pest species, and
concern has developed over environmental contamination by fertilizers and
pesticides. Increasing attention, therefore, is being given to means of reducing
the reliance of American farmers on highly chemical means of production. To
produce high yields, protect soil productivity, and maintain environmental
quality, farming must be based on an understanding of how water and dissolved
chemicals move through the plant-soil-groundwater system. The purpose of this
extension series is to build such understanding, and the remaining bulletins
explain how agricultural chemicals affect human health, how they get into
drinking water, and how such contamination can best be prevented.
For Further Reading
Clark, E.H. II, J.A. Haverkamp, and W. Chapman. 1985. Eroding soils: The off-
farm impacts. The Conservation Foundation, 1717 Massachusetts Ave, N.W.,
Washington, DC 20036.
Environment and Natural Resources Policy Division, Library of Congress. 1979.
Agricultural and environmental relationships: Issues and priorities. Printed for
the Committee on Science and Technology and the Committee on Agriculture, U.S.
House of Representatives, 96th Congress. U.S. Govt. Print. Off., Washington, DC
Office of Technology Assessment, Congress of the United States. 1982. Impacts of
technology on U.S. cropland and rangeland productivity. U.S. Govt. Print. Off.,
Washington, DC 20401.
Pimentel, D., et al. 1978. Benefits and costs of pesticide use in U.S. food
production. Bioscience 28: 772-84.
Rupnow, J., and C.W. Knox. 1975. The growing of America. 200 years of U.S.
agriculture. Johnson Hill Press, Inc., Fort Atkinson, Wis.
Acknowledgments: Illustrations were drawn by Christine Cleveland, and Mary Jane
Porter served as production assistant. Funding was provided by the New York
Farmers' Fund. Many individuals reviewed the initial drafts, including Cornell
University faculty members, northeastern Cooperative Extension agents, and
employees of the U.S. Department of Agriculture and U.S. Geological Survey.