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Modern Agriculture: Environmental Effects


Modern Agriculture: Its Effects on the Environment


Nancy M. Trautmann
Keith S. Porter
Center for Environmental Research
Robert J. Wagenet
Dept. of Agronomy
Cornell University

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 country.

Historical Perspective

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 single crop.

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 used.

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 pest populations.

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 groundwater.

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 20401.

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.