Crops and SoilEnvironmental ScienceChapter 15 Section 1

Crops and Soil• Arable land

o Land that can be used to grow crops.o Urban areas occupy about 3% of the Earth’s land surface and are

expanding into arable land.o Need to use the remaining arable land efficiently so we can grown

enough food for the world.

Agriculture: Traditional and Modern

• Basic process:o Plowing, fertilization, irrigation, pest control

• Traditionalo Plows are pushed by the farmer or pulled by livestock.o Organic fertilizers are used.o Irrigated by water flowing through ditches.o Weeds removed by hand or machine.

• Moderno Machinery is used to plow the soil and harvest crops.o Synthetic fertilizers are used.o Overhead sprinklers and drip systems are used for irrigation.o Synthetic chemicals are used to kill pests.

Fertile Soil: The Living Earth

• Fertile soilo Soil that can support the growth of healthy plants.

• Topsoilo The surface layer of soil.o Usually richer in organic matter than subsoil.

• Soil formationo Most forms when rock is broken down into smaller and smaller

fragments by wind, water, and chemical weathering.o Rock particles supply minerals.o Fungi and bacteria decompose dead plants and organic debris.o Earthworks, insects, small animals break up the soil to allow air and

water to pass through.

Fertile Soil: The Living Earth

Soil Erosion: A Global Problem

• Erosiono Movement of rock and soil by wind and water.o About half of the original topsoil has been lost to erosion in the past

200 years.o Need topsoil for plants to grow.o Most farming methods increase the rate of soil erosion.

Land Degradation• Occurs when human activity or natural processes

damage the land so it can no longer support the local ecosystem.

• Desertification can occur.o The process by which land in arid or semiarid areas becomes more

desertlike.

Soil Conservation• Methods

o Building soil-retaining terraces across a hillside.o Contour plowing – plowing across a slope instead of up and down the

slope.o Leave strips of vegetation on slopes.o No-till farming – harvest a crop without turning over the soil.

Enriching the Soil• Organic and inorganic fertilizers.

o Organic matter decomposes.o Inorganic fertilizers containing nitrogen, phosphorus, and potassium

are used.o Compost – partly decomposed organic material.

Salinization• Accumulation of salts in the soil.

• A big problem in CA and AZ – low rainfall and naturally salty soil.

• Soil can become so salty that plants cannot grow.

Pest Control• In North America, insects eat about 13% of all

crops.

• Even greater damage in tropical areas.

• Worldwide, destroy about 33% of potential food harvest.

• Pest – any organism that occurs where it is not wanted or that occurs in large enough numbers to cause economic damage.

Pest Control• Pesticides

o Chemicals used to kill insects, weeds, and other crop pests.o Many new pesticides invented over last 50 years.o Can also harm beneficial plants and insects, wildlife, and people.

Pest Control• Pesticide Resistance

o The ability to survive exposure to a particular pesticide.

• Human Health Concernso Can also harm humans.o Cancer rates and nervous system disorders are common where there is

high use.

• Pollution and Persistenceo Persistent pesticides do not break down rapidly into harmless

chemicals.o Ex: DDT

Biological Pest Control• The use of living organisms to control pests.

• Pathogenso Organisms that cause disease.

• Plant Defenseso Scientists and farmers have bred plant varieties that have defenses

against pests.o Chemical compounds that repel pests and physical barriers, such as

tougher skin.

• Chemicals from Plantso Biodegradable and less harmful to humans and pets.

Biological Pest Control• Disrupting Insect Breeding

o Growth regulator – chemical that interferes with some stage of a pest’s life cycle.

o Pheromones – chemicals produced by one organism that affect the behavior of another organism.

Integrated Pest Management

• Modern method of controlling pests on crops.

• Goal is to reduce pest damage to a level that causes minimal economic damage.

Engineering a Better Crop

• Plant breeding – famers select best plant candidates to grow.

• Genetic engineering – technology in which genetic material in a living cell is modified for medical or industrial use.

• Implicationso Many products have not been fully tested for environmental impact.

Sustainable Agriculture

• Sustainable agricultureo Farming that conserves natural resources and helps keep the land

productive indefinitely.

• Low-input farmingo Sustainable agriculture minimizes the use of energy, water, pesticides,

and fertilizers.