Agriculture: The science and practice of farming,

including the cultivation of the soil and the rearing of livestock.

Agriculture is considered to be a primary economic activity

Primary Economic Activity: Those that harvest or extract something from the Earth

Spatially the most widespread of the primary activities (15 million km2 worldwide - ±10% of the Earth’s surface area)

Basic Concepts

Subsistence Agriculture: Any of several farm

economies in which most of crops are grown for food nearly exclusively for local or commercial consumption Extensive Involves large areas of land and minimal labour input

per hectare (e.g. Nomadic herding) Intensive Involves the cultivation of small landholdings through

the expenditure of great amounts of labour per hectare Urban (e.g. small garden plots)

Basic Concepts

Commercial Agriculture: Farm economies where

production is not for their own subsistence, but primarily for a market off the farm itself Extensive Farther away from the market on less expensive land

there is less need to use the land intensively leading to larger farm units (e.g. maize farms)

Intensive Farmers who apply large amounts of capital (for

machinery, fertilizers etc.) and/or labour per unit land. Crops characterised by high yields and high market value

Basic Concepts

World Land Use (Arable Land)

Increasing population size leads to increased

pressure on agriculture land Increase in physiological density Physiological Density: The number of persons per

unit area of cultivable landWorld’s food supply influenced by social disruptions

and social attitudes Social instability makes sustained agricultural yields

difficult

Human Component

Starvation Undernourishment: Results from insufficient calories in

available food so that one has little or no ability to work or even move and eventually dies from a lack of energy Manifests as famines that are obvious, dramatic and fast

acting Malnourishment: Results from the lack of specific chemical

components of food, such as proteins, vitamins, or other essential chemical elements Long term and insiduous People may not die, but can suffer permanent impairment

and even brain damage

Human Component

Soil: a natural body composed of minerals, organic

compounds, living organisms, air and water in interactive combinations produced by physical, chemical and biological processes

Soil Horizons: Vertical differences in texture, colour, or structure

Soil Profile: Vertical section through all the soil horizons Soil Fertility: The capacity of a soil to supply nutrients

necessary for plant growth Important to realise that soil consists of ecosystems

WITHIN the soil

Soil

Soil Profile

Agriculture and the environment intimately

interconnected Soil and climatic conditions influence choice of

agricultural practice Agricultural practices can have negative impact on the

environment: Ecosystems Soil Physical Chemical

Surface water

Agricultural Impacts

Impacts interconnected and do not occur in isolation

Agroecosystems: An ecosystem created by agriculture.

Typically has low genetic, species, and habitat diversity Differ from natural ecosystems in six ways:

1. Ecological succession is halted to keep agroecosystem in early successional stage

2. Biological diversity and food chains are simplified3. The focus is monoculture4. Crops are planted in neat rows and fields5. Agroecosystems require ploughing6. They may include genetically modified crops

Ecological Perspective

Deforestation: Clearing of land through total removal of forest

cover Historically two most important reasons: Clearing land for Agriculture Settlement

Using the trees for: Lumber Paper products Fuel

Easter Island tragic example of consequences of deforestation Deforestation rate in 21st Century estimated at 73000 km2/year

Deforestation

Ecosystem impacts: Removal of late successional community Reduction of ecosystem complexity Loss of species Habitat destruction

Soil impacts: Accelerated erosion (loss of topsoil) Global loss: >5.62 million km2

Increases in soil compaction (decreased air and water content) Increased frequency of landslides

Surface water impacts: Increased sedimentation Changes in catchment hydrology

Deforestation

Rangeland: Provides food for grazing and browsing

animals without ploughing and planting Pasture: is ploughed, planted, and harvested to

provide forage for animalsMuch of world’s rangeland in poor condition from

overgrazing Impacts of grazing vary with density of herbivore

population (carrying capacity)

Grazing Practices

Ecosystem impacts Destruction of vegetation (due to trampling and

overgrazing) Loss of ecosystem structure

Soil impacts Compaction of soil surface Destruction of river banks

Surface water impacts Pollution by waste (excrement of cattle) Influences BOD

Increased sediment loads due to erosion

Grazing Practices

Soil Erosion in Systems Theory

Input:Soil Formation

Storage:Global Soil Reservoir(i.e. Global soils that can be used for agriculture)

Output:Loss of Soil(Erosion)

Irrigation Fertilizers: Used to correct nutrient deficiencies in plants

and animals and to improve growth and product quality Pesticides: Used to protect crops from pasts and disease

or to eliminate competition from weeds Four major changes due to industrial revolution:

1. Broad-Spectrum Inorganic Toxins2. Petroleum-Based Sprays and Natural Plant Chemicals3. Artificial Organic Compounds4. Integrated Pest Management and Biological Control

Some Agricultural Practices

Broad-Spectrum Inorganic Toxins Unsuccessful attempt to find “magic bullet” Early pesticides widely toxic One of the earliest was Arsenic Efficiently killed pests BUT ALSO beneficial organisms

Natural Plant Chemicals Plants produce chemicals as a defence against herbivores

and disease Make effective pesticides e.g. Nicotine (derived from tobacco) Safe to use but not as effective as desired

Pesticides

Artificial Organic Compounds e.g. DDT Can lead to secondary pest outbreak

1. Reduction of target species reduces competition with second species which can then become a pest

2. Pest develops resistance Compounds such as DDT are broad-spectrum but have

unexpected environmental effects Atrazine can cause demasculinization and feminization of

frogs Can remain in soil for years First breakdown product can also be toxic

Pesticides

Integrated Pest Management and Biological Control Integrated Pest Management: Control of agricultural pests

using several methods together, including biological and chemical agents. A goal is to minimize the use of artificial chemicals ; another goal is to prevent or slow the build-up of resistance by pests to chemical pesticides Moves away from monoculture growing in perfect rows No-till or low-till agriculture

Biological Control: A set of methods to control pest organisms by using natural ecological interactions, including predation, parasitism, and competition

Pesticides

Malthus vs. Boserup Several strategies1. Increased production per unit surface Genetically modified food Cornucopian theory

2. Increased farmland area Biofuels vs. agriculture

3. New crops and hybrids4. Better irrigation Drip irrigation

Keeping up With Human Population Growth

5. Organic farming Organic farming: Farming that is more ‘natural’ in the

sense that it does not involve the use of artificial pesticides and, more recently, genetically modified crops

6. Eating lower on the food chain

Keeping up With Human Population Growth

Desertification: The spread of desert-like conditions

in arid or semi-arid regions due to human interference or climatic change, or both

Eutrophication: Excessive growth of algae and other related organisms in a stream or lake as a result of the input of large amounts of nutrient ions, especially phosphate and nitrate

Soil salinization: Precipitation of soluble salts within the soil

Other Impacts

Genetically Modified Food Involves several different practices

1. Faster and more efficient ways to develop new hybrids• Risk of “superhybrids”• Interbreeding with closely related weeds (superweeds)

2. Introduction of the terminator gene• Seeds of a crop are sterile• Socio-economic implications

3. Transfer of genetic material from widely different kinds of life

• Transfer of genes from a bacterium to plant• Each cell in plant produces pesticide

Other Impacts