2006 自然科学の英語 -ENS-L6 Agricultural ecosystems - productivity L6 English in Natural Science 自然科学の英語

2006 自然科学の英語 -ENS-L6

Agricultural ecosystems - productivityL6

English in Natural Science

自然科学の英語


Ecology applied to agriculture• Aims

– To obtain the optimum yield– To achieve sustainable production

• Natural resources are limited• Ecosystems are NOT stationary

– Climate changes– Nutrient availability– Other: diseases, pests, weeds, predators, etc

• We are not alone: the Earth is not only for us– live in harmony with other creatures that share our planet– be able to cover our needs (food, clothing)– respect and let the rest of the natural world LIVE as well

• Humans = superpredators


Production systems• Agriculture

– Cultivation• Cereals (grain): rice, wheat, corn, barley, millet• Vegetables: soybean, potatoes, all green vegetables• Fruit: many kinds (trees)• Fibre: cotton, hemp

– Livestock• Grazing: cattle, sheep, goats AND wool, leather• Farm: dairy products, pigs, chicken

– Aquaculture: farming of fish (carp, trout, etc)

• Harvesting of natural ecosystems– Fisheries

• Fish• Shellfish• Whales

– Forests: timber, paper, natural products (resin, rubber)


Minimizing water losses• Number of stomata/leaf• Stomatal rythms (CAM)• Structural (hair,

cuticule)• Leaf shape• Water gradient (C4)

Factors in agricultural production• Light• Water• Nutrients

– CO2

– Others• N• P• S• K• Ca• Mg• Fe• Trace

elements

Limiting factors

Photosynthesis

CO2 intake H2O transpired

• C3 metabolism– CO2 fixed in phosphoglyceric

acid

• C4 metabolism– CO2 fixed in malic + aspartic

acids

• CAM metabolism– Dark-fixed CO2 (malic acid)– C3 diurnal metabolism


‘A given area of land can produce up to a certain limit’

• Limiting factors– Land availability– Physiological constraints– Environmental factors

• Light• Temperature• Water• Soil nutrients

– Pests and diseases

Productivity of agriculture

Green Revolution

Genetic improvement

Irrigation

Fertilizers

Chemical control


Agricultural land (m ha)

• Requirements:– Good soil (nutrients)– Appropriate climate

• Cropland/person– Reduced from 0.23 ha (1950) to 0.11 ha (2000)

• Threats– Urbanization ‘steals’ arable land: 2.8 m ha/year

• 0.04 ha/person

– Desertification: 9 m ha/year (?)– Car ownership: 400,000 ha/year

• 0.07 ha/car USA, Canada, Australia, Brazil• 0.02 ha/car EU, Japan, China, India

Cropland Grazing Total land

Already used 670 930 1,600

Yearly increase 3 4 7

Yearly losses 0.4 3.7 4.1

Total increase/year

3.4 7.7 11.1

Available 2,500 1,200 3,700


Physiological constraints• Each species has an upper physiological limit

C4 > C3

• Increases in productivity mainly due to genetic improvement (%)

Cultivated strains >> wild type– Polyploid varieties (wheat, corn)– Less leaf and more grain

• Dwarf wheat (Japan 1900s, Mexico 1950s)

– New strains adapted to temperature, light conditions• Winter wheat• Rice (China, 1700s, Japan 1880, IRRI 1960s)

• Methods– Selection of strains & varieties over centuries– Genetic manipulation


Light intensity and productivity

Country Yield (tons/ha)

France 6.8

Mexico 5.0

India 2.7

• Constraints to light– Latitude

• long daylight hours during growing period

Temperate > Tropical

– Climate pattern• sunny summer better than

cloudyMediterranean > Monsoon

• Threat– Climate change

• Cloudy pattern UP

Country Yield (tons/ha)

California 5.8

Spain/Australia 5.4

Japan/China 4.5

India 2.0

Wheat yields

Rice yields


Water and productivityProductivity ∞ soil moisture

1000 L water 1 kg grain

• Rain fed– Grazing land– Crops: wheat, barley

• Irrigated (25-60% efficiency)– Rivers– Groundwater (well)

• Rice, corn• Cotton• Green vegetables

% usage

Irrigation 70

Industry 20

Residential 10


Water availabilityH2O absorbed by roots by osmosis• Pore size in soil - surface tension (capillarity)• Osmotic pressure - nutrients, salts salination drying wilting waterlogging anaerobic rot

Soil texture

SandyDrain water

LoamyRetain-release water

ClayRetain water


Are we running out of water?

• Climate changes– More evaporation– More rainfall– Climate re-distribution

• Aquifer depletion– Rechargeable aquifers

rainfall supply ≥ usage– Fossil aquifers

• Great Plains USA• Saudi Arabia• North China Plain

Aquifers Rivers running dry

Afghanistan Amu Darya

China 27% gone Fen

Yellow

Egypt Nile

India

Pakistan

6 m/yr Ganges

Indus

Iran 5 b ton/yr

Israel gone

Mexico 1/3 total

Saudi Arabia 60% gone

USA 24% gone Colorado

Yemen 2 m/yr


Nutrient availability

• Nutrient content– N fixing micro-organisms

• Legume symbiosis

– Debris recycling• microorganisms• soil fauna

• Soil type – mineral composition

• Rich: volcanic, alluvial• Poor: acidic, sandy, tropical

(washed off)

• Soil structure– Horizons (layers)

• 0 and A rich in nutrients

– Texture• loam, clay, sand


Soil threats• Exhaustion of nutrients

– Intensive cropping nutrient depletion– Solutions

• Fallow: land put aside to recover fertility• Crop rotation using legumes (N2 fixation) = biofertilizers• Add fertilizers (NH4,urea, super-phosphates)

• Erosion = loss of soil– Agents: wind and water– Causes

• Tillage– plowing unprotected land after cultivation (bare soil)

• Overgrazing by livestock – animals/area > grassland carrying capacity

Ex tillage + Overgrazing erosion desertification

SUSTAINABLE

UNSUSTAINABLE


Desertification = land degradationsoil loss > soil formation

– Land fertility decreases– Human settlements move out– Dust storms increase contamination

Water Wind Total

Asia 158 153 311

Africa 119 160 279

Europe 48 39 87

Australasia 70 16 86

North America 38 38 76

South America 35 27 62

Total 468 433 901

Soil degradation (m ha) in the world (UNEP 1990)

Number

1950-59 5

1960-69 8

1970-79 13

1980-89 14

1990-99 23

Dust storms in China


Animal production• Products

– Meat– Skins: leather– Fibre: wool

• Meat efficiencykg grain / kg meat– Beef 7– Pork 3.5– Chicken 2– Fish 1.5

• 37% world grain used in meat production

Annual growth %

Aquaculture 9.7

Poultry 4.9

Pork 2.5

Mutton 1.6

Beef 0.8

Fish catch 0.8


The human ‘ecological footprint’ (2000)• Area per person: 0.5 ha -- 5 ha (USA)• Grain consumed per person (kg/yr)

200 India -- 400 Italy -- 800 USA

1 person World

Grain 252 kg 14 m tons

Meat 148 kg 8 m tons

Fish 15 kg 1 m tons

Water 520 m3 29 b m3

Land 0.5 ha 35 m ha

Vehicles 0.13 9 m


Grain production

• Rice & wheat stable for last 10 years

• Corn: still increasing

Rice

Wheat

Corn

Period Yield/ha

(tons)

Annual increase (%)

2000 2.79 1.2

1990 2.47 2.1

1980 2.00 1.9

1970 1.65 2.5

1960 1.29 2.0

1950 1.06

World grain yields (1950-2000) - various sources


Depletion of resources

• Aquifers in Middle-East (over-exploitation)

• Arable land in China (desertification)


The Japan syndrome• Development leads to

– Reduced agricultural production– Diversification of food imports– Reduction in women fertility

• Japan, South Korea, Taiwan…China?

Other country’soverproduction

STOCKS


Current trends

• Increased fish and seafood consumption– 85 m tons/year

(5 x 1950 production)

• Aquaculture– Most efficient way to

produce animal protein– Soya meal production


Deforestation= squandering

• Soybean Chinese aquaculture

– Brazil– Argentina

• Palm oil bio-fuel, cooking, detergent

– Indonesia– Malaysia products

Developedcountries

Developingcountries

demand

Natural resources

jobs

$ ¥

Free trade ?Irrational usage

2006 自然科学の英語 -ENS-L6 (Krebs, 2001)

Forestry: timber + products• Population dynamics of a forest vs productivity

– Saplings take more than 10-15 years to grow– Mature cohorts are better than old trees

sappling mature old


Harvesting: maximum yield• Obtained by

keeping a population at one-half the carrying capacity (K)

R + G = M + Y

R = recruitmentG = growthM = natural mortalityY = yield

Ymax = K/2


Optimum yieldEconomics• Yield = profit ($, ¥)• Aim: maximum profit

– Ymax is too costly

– Optimum yield < Ymax

Ecology• Aim: sustainable yield

– Ymax = K/2

– Optimum yield << K/2• fluctuations in natural

populations

• diseases, etc

Disease


Depleted fisheriesNorthern cod (Canada Fisheries, 1999)

Souther Hemisphere whales (Allen, 1980)

Red king crab (Alaska Fisheries, 1999)


References

• Lester R. Brown. 2004. Outgrowing the Earth. W.W. Norton, New York

• Charles J. Krebs. 2001. Ecology / 応用動物昆虫学　 B-226

Documents

2006 自然科学の英語 -ENS-L6 Agricultural ecosystems - productivity L6 English in Natural Science 自然科学の英語