Encyclopedia of Global Resources part 5 pot

Agricultural products Categories: Plant and animal resources; products from resources Agricultural products encompass all commodities de-rived from the production of animals and the grow

their durability and ability to be polished to an

attrac-tive gloss finish Examples include large building

or-naments, countertops, and headstones for graves

Sand and gravel are found in areas with past or

ex-isting streamflow In many cases, the segregating

as-pects of streamflow have sized the sand and gravel so

that further sizing is minimized Crushed stone,

how-ever, is produced in mining operations, and the

oper-ator has control over the size range of the finished

product For the most part, these operations are at the

surface and are known as quarries Some stone is

pro-duced in underground mining operations, with the

high quality of the stone justifying the additional

ex-pense of this type of operation Many quarries

operat-ing in a particularly desirable deposit of stone

con-tinue to pursue it by going underground

Preparations for Mining

Before any significant expense is committed to

locat-ing and developlocat-ing an aggregate production site, a

market study is performed to determine the amount

and quality of materials needed within a certain

ra-dius of transportation Experienced aggregate

pro-ducers usually have a “sixth sense” about the need for

and location of their products After the marketing

study has been completed, a quarry site is located by

geological exploration techniques such as

identifica-tion of surface outcrops of material or inference,

through regional studies of rock type Even surface

vegetation can indicate the type of material beneath

the surface Limestone terrains, for example, do not

support acidic-soil vegetation because of their high

pH values

The potential source of aggregate is identified and

outlined more precisely through the digging of test

pits for samples of the materials or by drilling test

holes and analyzing the samples obtained Again, the

inherent size of the naturally occurring materials and

the estimated expense of preparing them to market

specifications are critical points that help determine

whether a site is to be developed

If an aggregate site is to be produced, mineral

leases are obtained from the mineral owners, who

usually own the aggregate as well as deeper minerals

Sometimes the aggregate producer purchases the

property outright if the location is environmentally

sensitive or if a particularly long-lived aggregate

source is identified If the property is leased, the lease

is usually for a fixed term, perhaps ten years, with

op-tions to continue the lease for additional terms A

roy-alty is paid to the owner of the minerals according to the market value of the products The royalty usually varies from 2 percent to 10 percent of the aggregate’s selling price

After the quarry dimensions have been verified, applications to develop the site are made to the local, state, and federal agencies that will regulate all aspects

of site operation The effects of the mining operation

on air, groundwater and surface water, wildlife, ar-chaeological sites, and various natural processes must

be determined This process can be extremely expen-sive and consume several years An environmental im-pact study and report may be necessary in certain ar-eas This a very detailed and comprehensive report that incorporates all the environmental factors to be considered in locating the pit or quarry

Aggregate Mining Operations When all applicable permits and releases have been obtained, mining of the aggregate begins For sand and gravel, the products can be recovered using sim-ple excavation equipment such as front-end loaders, pan scrapers, or dredges The stone in quarries, how-ever, has inherent strength such that it is usually nec-essary to use explosives to fragment the material and make it suitable for bulk transport from the quarry Blasting is used to dislodge stone from the “face,” or quarry wall Almost any commercial explosive can be used for this purpose, but a mixture of ammonium ni-trate and fuel oil has emerged over the past several de-cades as the most cost-efficient explosive Dynamite is still used but in smaller quantities than before Several rows of blast holes are drilled at predeter-mined distances from the free quarry face These dis-tances are engineered to ensure efficient rock break-age without unnecessary “fly” rock, or rock that is propelled outside the desired blasting area Explosive cord is also extensively used in blasting operations This product, with an almost instantaneous ignition rate, is especially useful when “delay” blast rounds are used In delay blasting, millisecond delay sequences cause the first row of blast holes to be initiated, then subsequent rows rearward from the free face to be ig-nited after predetermined delays This technique, now standard in nearly all quarry blasting proce-dures, results in much greater blasting efficiency Dimension stone may also be removed by explo-sives, but the drill holes are very closely spaced, and the explosive is limited to the amount necessary to cut the block of dimension stone to the desired size and

not fragment it further

High-pres-sure water jets or rock-cutting saws

are also used in removing dimension

stone from the quarry Since the value

of the dimension stone depends on

the largest physical units minable,

the stone must be gently dislodged so

that it remains intact

Blasting, while indispensable to

the crushed stone industry, is also

one of the predominant problems

as-sociated with it The noise, vibration,

and dust resulting from blasting

op-erations, combined with the fact that

quarries are usually located near

populated areas, frequently bring

ongoing conflict between producers

and nearby residents As a result,

blasting is done carefully, and its side

effects are measured to ensure that it

is done within the guidelines set and

enforced by regulatory agencies

The blasted material, after it is removed from the

quarry face, is loaded by front-end loaders or shovels

into large trucks for transportation to the surface

preparation plant The timing of the quarry floor

loading operation is a continually challenging

prob-lem involving machinery size and speed, operator

ef-ficiency, and positioning Occasionally it is necessary

to reduce the sizes of blasted fragments that are too

large to be loaded and transported easily with existing

equipment, and small amounts of explosives may

again be necessary on the quarry floor

Transporta-tion from the quarry floor is usually by truck, belt

conveyor, or bucket conveyor, depending on the

oper-ating system in effect at the quarry Removal of

dimen-sion stone poses a special problem because the large

sizes demand gentle handling and require vehicles

ca-pable of transporting the large, heavy units of stone

Large track-mounted crawlers, rubber-tired vehicles,

or cranes are frequently used for this task

Sizing the Material

Blasted materials are transported from the quarry

to be reduced in size (“comminuted”) using

adjust-able crushers, sorted into various sizes to suit the

cus-tomer’s specifications, washed to remove unwanted

extraneous materials such as clays, and stockpiled

awaiting shipment Typically, crushers operate by

chewing on the material (“jaw crushers”) or passing

the material through rollers (“roll crushers”) When crushed, the material assumes sizes varying from dust-sized particles to pieces equivalent to the crusher open-ing Most of these crushed products, even the fine sizes, have some value, so the sizing operation is indispens-able to an efficient quarry serving multiple customers Sizing may be based on a number of physical prin-ciples, such as the ability to pass through or be re-jected by sized openings (sieving), the tendency to drop out of a fluid stream (liquid classification), or the ability to be propelled through the air to a certain distance (air classification) If the materials have par-ticular physical or chemical characteristics (magne-tism, for example), other sizing operations can be de-signed to take advantage of them Sieves (screens) frequently have a vibration device attached to them to prevent clogging and expedite the sorting process Screening can be fully wet or dry, but merely moist materials cannot be separated in a screening opera-tion

The end result of sizing is having several sized prod-ucts in which the size range within a sized product is quite narrow If necessary, sized materials can be fur-ther classified by washing techniques designed to re-move the fine sizes inherent in the crushing process Practical sizes of quarry products range from dust sizes of a few microns in diameter to cubic-shaped di-mension stone having didi-mensions exceeding 6 or 9

The sizes of sand can vary dramatically The large-grain sand, from England, is approxi-mately 2 millimeters in diameter The small-grain sand is from Tunisia.

meters For most applications, however, practical sizes

include sands from 1.65 millimeters through gravels

around 0.6 centimeter to 1.2 centimeters in diameter,

to stone sizes 2.5 centimeters to 7.6 centimeters in

diameter, to fist-sized material used for foundation

bases in construction, to football-sized riprap The

ul-timate goal of a stone and rock producer is to market

100 percent of the products generated in its

opera-tion While this is a practical impossibility, the most

efficient producers have been able to come

remark-ably close to this goal

Environmental and Citizenship Concerns

Virtually all the activities of quarry operation have

some undesirable side effects Siltation problems are

inherent in stream-based operations Blasting

gener-ates noise, dust, and vibrations Trucking activities do

the same, and they present a hazard to mixed

automo-bile traffic if public roads are used for transportation

Surface facilities are prone to emitting dust, and fluid

classification equipment produces sludge that must

be handled While not toxic in themselves, these

by-products from aggregate production are

objection-able and must be dealt with according to stringent

regulations from municipal, state, and federal

agen-cies The closer an aggregate producer is to populated

areas, the greater the inherent problems are (and the

harder it is for the producer to be considered a good

community citizen), but moving farther from these

areas brings increased transportation costs and may make the producer uncompetitive Moreover, most quarries are below the water table, which means that

a constant inflow of groundwater must be pumped to

a nearby creek or river Although this water is fre-quently used in the crushing and sizing processes, it must still be pumped, routed, stored, and eventually disposed Desludging equipment may also be neces-sary, further increasing the complexity of the opera-tion

Most successful aggregate producers have recog-nized and come to terms with the environmental con-sequences of their businesses Blasting procedures are carefully engineered to minimize unwanted side effects and are scheduled at times that are least objec-tionable to those living or working nearby A bag-house (a type of giant vacuum-cleaner bag) traps dusts produced by crushing operations and, in turn, frequently creates its own marketable product Elec-trostatic precipitators are also used to remove and col-lect dust-sized material Fines (powder or very small particles) from classification facilities are collected in sediment ponds that can be periodically “mined” to yield a marketable product In addition to being a good environmental citizen, an aggregate producer should have a visually pleasing facility if it is located in

or near populated areas Well-kept grounds, clean equipment, and storage areas free of debris are marks

of the conscientious operator

Crushed Stone Sold or Used in the United States, 2007

Number of Quarries Metric Tons

Total Value (dollars)

Unit Value (dollars)

Source: Data from U.S Bureau of Mines, Mineral Yearbook, 2007 U.S Government Printing Office, 2009.

Operational Life Span

Although a large sand and gravel pit or stone quarry

may remain open for decades, there is an ultimate life

span to each location Besides the restrictions of

min-ing to the edges of the deposit or to the legal property

limits of the miners’ leases, there is a practical depth

beyond which a quarry must either go underground

or face significantly increased costs of lifting the

mate-rial to the surface If the decision is made to abandon

the mine site, a large excavation remains that may

en-compass many hectares and be as much as 60 to 90

meters in depth With the closing of the pit or quarry,

the excavation quickly fills with water, and an

im-poundment, sometimes having very steep sides,

be-comes part of the landscape Topsoil initially removed

to expose the minable aggregate must be hauled away

or stored nearby Spoil that was removed and

dis-carded during the quarrying operation may now be

visually objectionable and must be remedied

If all these remedial activities are included as a part

of the overall life cycle of the pit or quarry, then a

desirable residential location may be created It is

common to see upscale housing developments built

around old pits and quarries, with the impoundments

becoming favorite targets of sport fishermen They

are also frequented by migratory birds and other

wild-life favoring large bodies of fresh water

Charles D Haynes

Further Reading

Blatt, Harvey, Robert J Tracy, and Brent E Owens

Pe-trology: Igneous, Sedimentary, and Metamorphic 3d ed.

New York: W H Freeman, 2006

Chatterjee, Kaulir Kisor Uses of Industrial Minerals,

Rocks, and Freshwater New York: Nova Science,

2009

Grotzinger, John P., et al Understanding Earth 5th ed.

New York: W H Freeman, 2007

Hockensmith, Charles D The Millstone Industry: A

Summary of Research on Quarries and Producers in the

United States, Europe, and Elsewhere Jefferson, N.C.:

McFarland, 2009

Kogel, Jessica Elzea, et al., eds “Stone and Rock.”

In-dustrial Minerals and Rocks: Commodities, Markets,

and Uses 7th ed Littleton, Colo.: Society for

Mining, Metallurgy, and Exploration, 2006

Philpotts, Anthony R., and Jay J Ague Principles of

Ig-neous and Metamorphic Petrology 2d ed New York:

Cambridge University Press, 2009

Raymond, Loren A Petrology: The Study of Igneous,

Sedi-mentary, and Metamorphic Rocks 2d ed Boston:

McGraw-Hill, 2002

Smith, M R., and L Collis, eds Aggregates: Sand,

Gravel, and Crushed Rock Aggregates for Construction Purposes 3d ed Revised by P G Fookes et al

Lon-don: Geological Society, 2001

Tarbuck, Edward J., and Frederick K Lutgens Earth:

An Introduction to Physical Geology 9th ed Illustrated

by Dennis Tasa Upper Saddle River, N.J.: Pearson Prentice Hall, 2008

Weiss, Norman L., ed SME Mineral Processing

Hand-book 2 vols New York: Society of Mining Engineers

of the American Institute of Mining, Metallurgical, and Petroleum Engineers, 1985

Web Sites Natural Resources Canada Canadian Minerals Yearbook, Mineral and Metal Commodity Reviews

http://www.nrcan-rncan.gc.ca/mms-smm/busi-indu/cmy-amc/com-eng.htm

U.S Geological Survey Crushed Stone: Statistics and Information http://minerals.usgs.gov/minerals/pubs/

commodity/stone_crushed/index.html#mcs U.S Geological Survey

Dimension Stone: Statistics and Information http://minerals.usgs.gov/minerals/pubs/

commodity/stone_dimension/index.html#mcs See also: Abrasives; Cement and concrete; Dimen-sion stone; Granite; Igneous processes, rocks, and mineral deposits; Limestone; Marble; Metamorphic processes, rocks, and mineral deposits; Quarrying; Sand and gravel; Slate

Agricultural products

Categories: Plant and animal resources; products from resources

Agricultural products encompass all commodities de-rived from the production of animals and the growing

of crops to be used by humans for food, fiber, shelter, me-dicinal applications, or aesthetic purposes.

A nation’s ability to sustain an agricultural system with

the capacity to feed, shelter, and clothe its population

is perhaps its greatest natural resource The human

domestication of certain animals and cultivation of

certain food crops predate written history In modern

society, the diversity of products that can be produced

via agricultural technology is enormous Major

agri-cultural commodities can be divided into those that

come from animals and those that are derived from

plants

Agricultural Products from Animals

The major animal-derived products can be divided

into edible and inedible red meat products, milk and

milk products, poultry and egg products, and wool

and mohair Red meat products refer primarily to

those products that come from cattle (beef and veal),

swine (pork), sheep (lamb and mutton), goats

(chevon), and, to a lesser extent, other animals

such as horses and buffalo

Other than the meat itself, edible products

from red meat animals include meat scraps used

to make processed meats such as frankfurters and

bologna; organ meats such as liver, tail, tongue,

tripe (stomach), and sweetbread (thymus); and

tallow or lard The major inedible red meat

prod-ucts include rendered fat, which is used to make

soap and formula animal feeds; bone meal, used

in fertilizer and animal feeds; manure; and hides

or skins, which are tanned and used to make

leather products

Milk and milk products, also referred to as

dairy products, are major components of the

hu-man diet in hu-many countries Whole milk with part

or all of the fat removed is sold as low-fat or skim

milk Evaporated and condensed milk refers to

milk from which approximately 60 percent of the

water has been removed, and dry or powdered

milk has had at least 95 percent of the water

re-moved Cultured milk products such as

butter-milk, yogurt, sour cream, and cottage cheese are

produced via fermentation by the addition of

ap-propriate bacterial cultures to fluid dairy

prod-ucts Cream products are separated from liquid

milk and have a milk fat content of not less than

18 percent Butter is made by separating the

but-terfat from either milk or cream and contains at

least 80 percent by weight milk fat Cheese is

pro-duced through the microbial action of a variety of

bacteria and fungi on whole milk Ice cream, ice milk, sherbet, and frozen custard are produced by freezing

a variety of liquid milk products in combination with sugar and other ingredients

Poultry products are nutritious and relatively inex-pensive, and they are used by humans throughout the world Broiler chickens provide most of the world’s poultry meat, but turkeys, roaster chickens, mature laying hens (fowl), ducks, geese, pigeons, and guinea hens are also consumed and may be more important than chickens in some parts of the world Much of the poultry meat is processed into preformed products such as poultry rolls or nuggets, canned products, or cured and ground products such as frankfurters, bo-logna, turkey ham, or salami Other than meat, poul-try also provides eggs The majority of the world’s eggs are now produced by chickens specifically selected to lay large numbers of eggs, but eggs from the other birds listed above are sometimes eaten Eggs can be

Harvested corn is loaded onto a grain-hauling truck (AP/Wide

World Photos)

further processed and sold as liquid eggs or dried

eggs There is also an industry based on the meat and

eggs from the ratite birds, such as the ostrich and emu

The hair covering the skin of some farm animals is

also considered an agricultural product The two most

important of these are wool from sheep and mohair

from angora goats Wool or mohair can be sheared

annually from the same sheep or goat The cleaned

and processed fibers are woven into yarn, which can

then be used to make carpet or cloth

Agricultural Products from Plants

Agricultural products that are derived from plants

are also diverse They can be subdivided into timber

products, grain crops, fiber crops, fruit crops, nut

crops, vegetable crops, beverage crops, spice and drug

crops, ornamental crops, forage crops, and other cash

crops such as sugarcane, tobacco, artichoke, and

rub-ber Timber products include those materials derived

from the trees of renewable forests The two major

products are lumber for building and paper, but

other products such as pine tar, resin, and turpentine

are also extracted from trees

More cultivated land is devoted to the production

of grain crops, also known as cereal grains, and fiber

crops than to any other agricultural crop Cereal

grains are the edible seed from a variety of grasses

Throughout history, these crops have been primarily

responsible for sustaining large human populations

and domestic animal herds The products from the

world’s major grain crops include corn, wheat, oats,

barley, rye, rice, and derivatives such as grain-based

cereals and flours Rice is the leading seed crop in the

world and is the principal food crop of about half the

world’s population Corn, barley, rye, and rice are also

used to produce alcoholic beverages Grain sorghums

are also produced in large quantities in the United

States, but this grain is primarily used as feed for

live-stock Cotton, flax, and hemp are the principal fiber

plants grown in the United States, although less

im-portant crops such as ramie, jute, and sisal are also

grown While these plants are grown primarily for

their fiber, which is used to make textiles, rope, twine,

and similar products, other products such as

cotton-seed oil and lincotton-seed oil from flax are also produced

Fruits from a variety of perennial plants are

har-vested for their refreshing flavors and nourishment

Fruits can be subdivided into temperate, subtropical,

and tropical crops Grapes, a temperate fruit grown

for table use, winemaking, and raisins, account for

ap-proximately 25 percent of the fruit production of the world Examples of other temperate fruits include the pome fruits (apple and pear), stone fruits (plum, peach, apricot), kiwi fruit, and berry fruits (straw-berry, rasp(straw-berry, black(straw-berry, cran(straw-berry, and blue-berry) Tropical and subtropical fruit crops include banana, pineapple, mango, papaya, avocado, date, fig, olive, and citrus fruits (orange, lemon, and grape-fruit) In addition to providing fresh fruit, the prod-ucts from fruit crops can be canned, dried, converted

to juices, and used to make jams and jellies or special products such as olive oil

Nut crops refer to those woody plants that produce seed with firm shells that separate them from an inner kernel Nuts are generally considered to be luxury food They are often eaten as a delicacy (either fresh

or canned) or consumed with candy or other sweets Major temperate nut crops include walnut, almond, chestnut, pistachio, pecan, and hazelnut Tropical nut crops include the coconut, cashew, Brazil nut, and macadamia Nuts are characteristically rich in oil The inedible tungnut is grown exclusively for its oil Vegetable crops are extremely diverse and range from starchy calorie sources (potato) to food that sup-plies vitamins and minerals (broccoli) Examples of the major vegetable crops include the edible legumes (beans, soybeans, peas, lentils, and peanuts); roots, tubers, and bulbs (potato, sweet potato, taro, yam, cas-sava, onion, sugar beet, and carrot); solanaceous fruits (tomato, eggplant, and chili pepper); salad plants (lettuce, endive, chicory, parsley, and garden cress); cole crops (cabbage, cauliflower, broccoli, brussels sprouts, and radish); and vine crops (cucumbers, wa-termelon, cantaloupe, pumpkin, squash, and gourd) Like fruit crops, vegetable produce can be served fresh, canned, frozen, or in an assortment of juices The world’s three most popular nonalcoholic bev-erages—coffee, tea, and cocoa—are produced in the tropics These products represent a major proportion

of the tropical world’s agricultural exports, and their production is the major industry in many tropical countries Many plants or plant parts that possess strong aroma and flavor are grown for the purpose of producing spices Because of the diverse biochemis-try of plants, some crops are cultured for the produc-tion of medicinal drug compounds There are more than two hundred spice and drug plants; some of the more common products are peppermint, nutmeg, garlic, vanilla, allspice, cinnamon, black pepper, mus-tard, opium, quinine, belladonna, and digitalis

Ornamental and forage crops are not consumed by

humans Ornamental crops are grown for aesthetic

purposes and are divided into florist crops (flower

and foliage plants) and landscape crops (nursery

plants) Common ornamental crops include rose,

or-chid, carnation, chrysanthemum, and a variety of

shrubs Forage crops are grown to feed livestock and

include a host of small grain grasses, clover, alfalfa,

and a variety of straw crops for haymaking

D R Gossett

Further Reading

Akinyemi, Okoro M Agricultural Production: Organic

and Conventional Systems Enfield, N.H.: Science

Publishers, 2007

Brody, Aaron L., and John B Lord, eds Developing New

Food Products for a Changing Marketplace 2d ed Boca

Raton, Fla.: CRC Press/Taylor & Francis, 2008

Field, Thomas G., and Robert E Taylor Scientific Farm

Animal Production: An Introduction to Animal Science.

9th ed Upper Saddle River, N.J.: Prentice Hall,

2008

Janick, Jules Horticultural Science 4th ed New York:

W H Freeman, 1986

Ward, Janet D., and Larry T Ward Principles of Food

Science Tinley Park, Ill.: Goodheart-Willcox, 2002.

Web Sites

Agriculture and Agri-Food Canada

Producers

http://www4.agr.gc.ca/AAFC-AAC/display-afficher.do?id=1165871799386&lang=eng

U.S Department of Agriculture

Animal Production

http://www.usda.gov/wps/portal/!ut/p/_s.7_0_A/

7_0_1OB?navid=ANIMAL_PRODUCTION&pare

ntnav=AGRICULTURE&navtype=RT

U.S Department of Agriculture

Crop Production

http://www.usda.gov/wps/portal/!ut/p/_s.7_0_A/

7_0_1OB?navid=CROP_PRODUCTION&parent

nav=AGRICULTURE&navtype=RT

See also: Agriculture industry; Corn; Horticulture;

Monoculture agriculture; Plant domestication and

breeding; Plant fibers; Plants as a medical resource;

Rice; Rubber, natural; Sugars; Wheat; Wood and

timber

Agriculture industry

Categories: Plant and animal resources; obtaining and using resources

The ability to produce sufficient food and fiber to feed and clothe its population is the most important natu-ral resource a nation can have In modern urban soci-eties, it is also the natural resource that is most often taken for granted.

Background The beginnings of agriculture predate the written his-tory of humankind No one knows when the first crop was cultivated, but at some time in the distant past hu-mans discovered that seeds from certain wild grasses could be collected and planted in land that could be controlled, the end product of which could later be gathered for food Most authorities believe this oc-curred at about the same time in both the Old World and New World, some eight thousand to ten thousand years ago The earliest attempts at growing crops were primarily to supplement the food supply provided by hunting and gathering However, as the ability to pro-duce crops increased, people began to domesticate animals, and their reliance on hunting and gathering decreased, allowing the development of permanent human settlements

As far back as six thousand years ago, agriculture was firmly established in Asia, India, Mesopotamia, Egypt, Mexico, Central America, and South America The earliest agricultural centers were located near large rivers that helped maintain soil fertility by the deposition of new topsoil with each annual flooding cycle As agriculture moved into regions that lacked the annual flooding of the large rivers, people began

to utilize a technique known as slash-and-burn agri-culture In this type of agriculture, a farmer clears a field, burns the trees and brush, and farms the field After a few years, soil nutrients become depleted, so the farmer must repeat the process This type of agri-culture is still practiced in some developing countries and is one reason that the tropical rain forests are dis-appearing at such a fast rate

Until the nineteenth century, most farms and ranches were family-owned, and most farmers prac-ticed sustenance agriculture: Each farmer or rancher produced a variety of crops sufficient to feed himself and his family as well as a small excess to be sold for

cash or bartered for other goods or services

Agricul-tural tools such as plows were made of wood, and

al-most all agricultural activities required human or

ani-mal labor This situation placed a premium on large

families to provide the help needed to tend the fields

The Industrial Revolution changed agriculture just as

it did almost all other industries Eli Whitney invented

the cotton gin in 1793 The mechanical reaper was

in-vented by Cyrus McCormick, and John Lane and John

Deere began the commercial manufacture of the steel

plow in 1833 and 1837, respectively These inventions

led the way for the development of the many different

types of agricultural machinery that resulted in the

mechanization of most farms and ranches By the

early part of the twentieth century, most agricultural

enterprises in the United States were mechanized

The Industrial Revolution produced a significant

change in society The industrialized nations were

gradually transformed from agrarian societies into

ur-ban societies People involved in agricultural

produc-tion left the farms to go to the city to work in the facto-ries At the same time, there was no longer a need for large numbers of people to produce crops As a result, fewer people were required to produce more agricul-tural produce for an increasing number of consum-ers This trend continues in developing nations with more rural dwellers, adding to the overcrowding in urban centers

Modern Agriculture

As populations continued to grow, there was a need to select and produce crops with higher yields The Green Revolution of the twentieth century helped

to make these higher yields possible Basic informa-tion supplied by biological scientists allowed the agri-cultural scientists to develop new, higher-yielding vari-eties of numerous crops, particularly the seed grains that supply most of the calories necessary for main-tenance of the world’s population These higher-yielding crop varieties, along with improved farming

A farm manager practices weed control in a soybean field as an aspect of the farm’s weed-tillage system (United States Department of

Agriculture/Keith Weller)

methods, resulted in tremendous increases in the

world’s food supply The new crop varieties also led to

an increased reliance on monoculture While the

practice of growing only one crop over a vast number

of hectares has resulted in much higher yields than

planting multiple crops, it has also decreased the

ge-netic variability of many agricultural plants, increased

the need for commercial fertilizers, and produced an

increased susceptibility to damage from a host of

bi-otic and abibi-otic factors These latter two

develop-ments have resulted in a tremendous growth in the

agricultural chemical industry Today’s modern

ag-ricultural unit requires relatively few employees, is

highly mechanized, devotes large amounts of land to

the production of only one crop, and is highly reliant

on agricultural chemicals such as fertilizers and

pesti-cides

Agricultural Diversity

With all the diversity that has occurred in modern

ag-riculture, the industry is subdivided into many

differ-ent specialties On the animal side of the industry,

there is the beef industry, which deals with the

pro-duction of beef cattle; the dairy industry, which

fo-cuses on the production of dairy cattle, milk, and milk

products; the horse industry, which produces horses

for work, sport, or pleasure; the sheep and goat

indus-try; the swine industry, which deals with the

produc-tion of pigs and hogs; and the poultry industry, which

is concerned with the production of commercial birds

and bird products such as eggs Those agricultural

in-dustries that deal with plants include agronomy, the

production of field crops (wheat, cotton, and so on);

forestry, the growth and production of trees; and

hor-ticulture Horticulture is subdivided into pomology,

the growth and production of fruit crops (oranges,

apples, and so on); olericulture, the growth and

pro-duction of vegetable crops (tomatoes, lettuce);

land-scape horticulture, the growth and production of

trees and shrubs that are used in landscape design;

and floriculture, the growth and production of

flow-ering plants used in the floral industry

The various agriculture industries produce a

tre-mendous number of different agricultural products

Those agricultural products that are derived from

plants can be subdivided into timber products (such

as lumber, furniture), grain products (wheat, oats),

fiber products (cotton, flax), fruit products (grapes,

peaches), nut crops (pecans, hazelnuts), vegetable

products (lettuce, cabbage), beverage products (tea,

coffee), spice and drug crops (garlic, mustard, opium, quinine), ornamental crops (carnation, chry-santhemum), forage crops (alfalfa, clover), and other cash crops, such as sugarcane, tobacco, artichoke, and rubber

The animal industries provide products such as red meats from cattle (beef and veal), swine (pork), sheep (lamb and mutton), and goats (chevon) Milk and milk products, also referred to as dairy products, in-clude milk, ice cream, and cheeses Broiler chickens provide most of the world’s poultry meat, but turkeys, roaster chickens, mature laying hens (fowl), ducks, geese, pigeons, and guinea hens are also consumed and may be more important than chickens in some parts of the world Other than meat, poultry also pro-vides eggs The hair covering the skin of some farm animals is also considered an agricultural product The two most important of these are wool from sheep and mohair from angora goats

Impact on Other Natural Resources While there have been tremendous increases in cultural productivity through the use of modern agri-cultural practices, these same practices have had a sig-nificant impact on some other natural resources Soil

is one of the most overlooked and misunderstood re-sources Most people think of soil as an inert medium from which plants grow In reality, topsoil—that up-per 15 to 25 centimeters of the Earth’s terrestrial sur-face in which nearly all plants grow—is a complex mixture of weathered mineral materials from rocks, partially decomposed organic molecules, and a large number of living organisms The process of soil for-mation is very slow Under ideal conditions, topsoil can form at a rate sufficient to produce a layer of about 1 millimeter thick when spread over 1 hectare per year Under less favorable conditions, it can take thousands of years to produce this small amount of soil With proper management, topsoil can be kept fertile and productive indefinitely However, many ag-ricultural techniques lead to the removal of trees and shrubs, which provide windbreaks, or to the depletion

of soil fertility, which reduces the plant cover over the field These practices have exposed the soil to in-creased erosion from wind and moving water, and as a result, as much as one-third of the world’s current croplands are losing topsoil faster than they can be re-placed

Because plants require water in order to grow, agri-culture represents the largest single global user of

water Worldwide, about 70 percent of all fresh water

withdrawn from groundwater supplies, rivers, and

lakes is used to irrigate crops, and almost 15 percent

of the world’s croplands are irrigated Water usage

varies among countries Some countries have

abun-dant water supplies and irrigate liberally, while water

is scarce in other countries and must be used carefully

Because as much as 60 percent of the water intended

for irrigation is lost through old pipes and canals or

to evaporation before the water reaches the field,

the efficiency of water use in some countries can be

very low There is no doubt that irrigation has

dra-matically increased crop production in many areas,

but some irrigation practices have been detrimental

Overwatering can lead to a waterlogging of the soil

Waterlogging cuts off the supply of oxygen to the

roots, and the plants die Irrigation of crops in dry

cli-mates can often result in salinization of the soil In

these climates, the irrigation water rapidly evaporates

from the soil, leaving behind the mineral salts that

were dissolved in the water As the salts accumulate,

they become lethal to most plants Some experts

esti-mate that as much as one-third of the world’s

agricul-tural soil has been damaged by salinization There is

also an argument as to whether or not the increased

usage of water for agriculture has decreased the

sup-ply of potable water fit for other human uses

Plants require sunshine, water either from rainfall

or irrigation, carbon dioxide from the atmosphere,

and thirteen mineral nutrients from the soil Of these,

calcium, magnesium, nitrogen, phosphorus, and

po-tassium are required in the greatest amounts

Cal-cium and magnesium are plentiful in soils located in

dry climates, but in wetter climates, these nutrients

are often leached through the soil In these regions,

calcium and magnesium are returned to the soil in

the form of lime, which is primarily used to raise the

soil pH Nitrogen, phosphorus, and potassium are the

nutrients most often depleted from agricultural soils,

and these nutrients are often referred to as the

fertil-izer elements Because these nutrients stimulate plant

growth and usually greatly increase crop yields, it is

necessary to apply them to the soil regularly in order

to maintain fertility

The amount of fertilizer applied to the soil has

in-creased more than twentyfold in the past fifty years

While this increase in the use of fertilizers has more

than tripled the worldwide crop production, it has

also caused some problems The increased

produc-tion of fertilizers has required the use of energy and

mineral resources that could have been used else-where In many cases, farmers tend to overfertilize Overfertilization not only wastes money but also con-tributes to environmental degradation Fertilizer ele-ments, particularly nitrogen and phosphorus, are carried away by water runoff and are eventually de-posited in the rivers and lakes, where they contribute

to pollution of aquatic ecosystems In addition, ni-trates can accumulate in underground water supplies These nitrates can be harmful if ingested by new-borns

Modern agriculture, as it is practiced in the indus-trialized nations, consumes large amounts of energy Farm machinery utilized in planting, cultivating, har-vesting, and transporting crops to market consumes the largest supplies of liquid fossil fuels such as gaso-line or diesel The energy required to produce fertiliz-ers, pesticides, and other agricultural chemicals is the

An agronomist cradles a box of broccoli on a farm in Salinas, Cali-fornia (United States Department of Agriculture)