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
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
2006
自然科学の英語-ENS-L6
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)
2006
自然科学の英語-ENS-L6
Factors in agricultural production
• Light
• Water
• Nutrients
Limiting
factors
Minimizing water losses
•
•
•
•
•
2006
Number of
stomata/leaf
Stomatal rythms
(CAM)
Structural (hair,
cuticule)
Leaf shape
Water gradient (C4)
– CO2
– Others
•
•
•
•
•
•
•
•
Photosynthesis
CO2 intake  H2O transpired
N
•
P
S
•
K
Ca
Mg
•
Fe
Trace
elements
自然科学の英語-ENS-L6
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
Productivity of agriculture
‘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
Genetic improvement
Irrigation
Fertilizers
– Pests and diseases
2006
Green Revolution
自然科学の英語-ENS-L6
Chemical control
Agricultural land (m ha)
• Requirements:
– Good soil (nutrients)
– Appropriate climate
• Cropland/person
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
2,500
1,200
3,700
Available
– 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
2006
• 0.07 ha/car USA, Canada, Australia, Brazil
• 0.02 ha/car EU, Japan,
China, India
自然科学の英語-ENS-L6
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
2006
自然科学の英語-ENS-L6
Light intensity and productivity
• Constraints to light
Wheat yields
– Latitude
• long daylight hours during
growing period
Temperate > Tropical
– Climate pattern
• sunny summer better than
cloudy
Mediterranean > Monsoon
Country
Yield (tons/ha)
France
6.8
Mexico
5.0
India
2.7
Rice yields
Country
• Threat
– Climate change
• Cloudy pattern UP
2006
Yield (tons/ha)
California
5.8
Spain/Australia
5.4
Japan/China
4.5
India
2.0
自然科学の英語-ENS-L6
Water and
productivity
Productivity ∞ soil moisture
1000 L water  1 kg grain
% usage
• Rain fed
– Grazing land
– Crops: wheat, barley
Irrigation
70
Industry
20
Residential
10
• Irrigated (25-60% efficiency)
– Rivers
– Groundwater (well)
• Rice, corn
• Cotton
• Green vegetables
2006
自然科学の英語-ENS-L6
Water availability
H2O absorbed by roots by osmosis
• Pore size in soil - surface tension (capillarity)
• Osmotic pressure - nutrients, salts
salination  drying  wilting
waterlogging  anaerobic rot
Soil texture
Sandy
Drain water
Loamy
Retain-release water
Clay
Retain water
2006
自然科学の英語-ENS-L6
Are we running out of water?
• Climate changes
– More evaporation
– More rainfall
– Climate re-distribution
• Aquifer depletion
Aquifers
Afghanistan
China
– Rechargeable
rainfall supply ≥ usage
– Fossil aquifers
• Great Plains USA
• Saudi Arabia
• North China Plain
2006
Amu Darya
27% gone
Egypt
India
aquifers Pakistan
Rivers
running dry
Fen
Yellow
Nile
6 m/yr
Iran
5 b ton/yr
Israel
gone
Mexico
1/3 total
Ganges
Indus
Saudi Arabia 60% gone
USA
24% gone
Yemen
2 m/yr
自然科学の英語-ENS-L6
Colorado
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
2006
自然科学の英語-ENS-L6
Soil threats
• Exhaustion of nutrients
SUSTAINABLE
– 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
UNSUSTAINABLE
– 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
2006
自然科学の英語-ENS-L6
Desertification = land degradation
soil loss > soil formation
– Land fertility decreases
– Human settlements move out
– Dust storms increase  contamination
Soil degradation (m ha) in the world (UNEP 1990)
Water
Wind
Total
Asia
158
153
311
Dust storms in China
Number
2006
1950-59
5
Africa
119
160
279
1960-69
8
Europe
48
39
87
1970-79
13
Australasia
70
16
86
1980-89
14
North America
38
38
76
1990-99
23
South America
35
27
62
Total
468
433
901
自然科学の英語-ENS-L6
Animal production
• Products
– Meat
– Skins: leather
– Fibre: wool
• Meat efficiency
kg grain / kg meat
– Beef
7
– Pork
3.5
– Chicken
2
– Fish
1.5
• 37% world grain used
in meat production
2006
自然科学の英語-ENS-L6
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
0.13
9m
Vehicles
2006
自然科学の英語-ENS-L6
Grain production
Rice
Wheat
• Rice & wheat stable for last 10
years
• Corn: still increasing
World grain yields (1950-2000) - various sources
Period
Corn
2006
Annual increase
(%)
2000
Yield/ha
(tons)
2.79
1990
2.47
2.1
1980
2.00
1.9
1970
1.65
2.5
1960
1.29
2.0
1950
1.06
自然科学の英語-ENS-L6
1.2
Depletion of resources
• Aquifers in Middle-East (over-exploitation)
• Arable land in China (desertification)
2006
自然科学の英語-ENS-L6
The Japan syndrome
• Development leads to
– Reduced agricultural production
– Diversification of food  imports
– Reduction in women fertility
Other country’s
overproduction
• Japan, South Korea, Taiwan…China?
2006
自然科学の英語-ENS-L6
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
2006
自然科学の英語-ENS-L6
Deforestation
= squandering
• Soybean 
Chinese
aquaculture
– Brazil
– Argentina
• Palm oil 
bio-fuel,
cooking,
detergent
– Indonesia
– Malaysia
2006
Developed
countries
$ ¥
demand
Developing
countries
Free trade ?
Irrational usage
products
自然科学の英語-ENS-L6
jobs
Natural
resources
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
2006
mature
old
自然科学の英語-ENS-L6
(Krebs, 2001)
Harvesting: maximum yield
• Obtained by
keeping a
population at onehalf the carrying
capacity (K)
R+G=M+Y
R = recruitment
G = growth
M = natural mortality
Y = yield
Ymax = K/2
2006
自然科学の英語-ENS-L6
Optimum yield
Economics
• Yield = profit ($, ¥)
• Aim: maximum profit
Ecology
• Aim: sustainable yield
– Ymax is too costly
– Optimum yield < Ymax
• fluctuations in natural
populations
• diseases, etc
2006
自然科学の英語-ENS-L6
– Ymax = K/2
– Optimum yield << K/2
Disease
Depleted fisheries
Red king crab (Alaska Fisheries, 1999)
Northern cod (Canada Fisheries, 1999)
Souther Hemisphere whales
(Allen, 1980)
2006
自然科学の英語-ENS-L6
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
2006
自然科学の英語-ENS-L6