materi kuliah ekologi tanaman 2011

AGROTEKNOLOGIAGROTEKNOLOGI

Lecturing ContractLecturing Contract

• Rules of attending the class

# max. 15’ lately # noisy forbidden

# keep HP silent # fit dressing

• Presence at least 75%

• Grading: >= 80 A Distribution

66 – 79,9 B Mid exam 25%

56 – 65,9 C Assignment 20%

46 – 55,9 D Course Prac 30%

<= 45,9 E Final exam 25%

• Attainment of Crop Ecology course (Competency map)

JadwalJadwal KuliahKuliah dandan PraktikumPraktikum

JADWAL KULIAHJADWAL KULIAH

MATERI PRAKTIKUMMATERI PRAKTIKUM

SUMBER PUSTAKASUMBER PUSTAKA

Scope of Ecology

Ecology is primarily concerned with

those biological (and Biogeochemical)

processes that control the functioning

of populations, communities, and

ecosystems over large spatial

(communities to global) and long

temporal (days-millennia) scales.

Ecosystem Properties:Ecosystem Properties:

• Structure:

Species diversity: plants, animals, and microbes; Community structure; Food-web structure; Soil type: structure, texture; Carbon and Nutrient Pools

• Function:

Energy capture (primary productivity, yield); Energy flow; Nutrient cycling; Population regulation; Stability and flexibility; Disturbance regime; Succession.

BIODIVERSITY

•What is Biological Diversity or Biodiversity?

• Biodiversity or biological diversity is defined by the United Nations Convention on Biological Diversity as:

"The variability among living organisms from all sources, including, inter alia [among other things], terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part: this includes diversity within species, between species and of ecosystems."

Within that definition, there are 3 distinct levels of biodiversity:

• Species diversity: diversity among species present in different ecosystems. This is the diversity of populations of organisms and species and the way they interact.

• Genetic diversity: diversity of genes within a species and processes such as mutations, gene exchanges, and genome dynamics that occur at the DNA level and generate evolution.

• Ecosystem diversity: genetic, species, and ecosystem diversity of a given region. This is the diversity of species interactions and their immediate environment.

Why is biodiversity important?Why is biodiversity important?All species are an integral part of their ecosystem by performing specific functions that are often essential to their ecosystems and often to human survival as well. Some of the functions different species provide are to:

• Capture and store energy

• Produce organic material

• Decompose organic material

• Cycle water and nutrients

• Control erosion or pests

• Help regulate climate and atmospheric gases

• We have an ethical responsibility to protect biodiversity.

Why is biodiversity important?Why is biodiversity important?

• Ecosystem diversity is important for primary production in terms of:

• Soil fertility

• Plant pollination

• Predator control

• Waste decomposition

• Removing species from ecosystems removes those important functions. Therefore, the greater the diversity of an ecosystem the better it can maintain balance and productivity and withstand environmental stressors.

Why is biodiversity important?Why is biodiversity important?• Biodiversity is important economically in

terms of:

• Food resources: agriculture, livestock, fish

and seafood

• Biomedical research: coral reefs are home

to thousands of species that may be

developed into pharmaceuticals to maintain

human health and to treat and cure disease

• Industry: textiles, building materials,

cosmetics, etc.

• Tourism and recreation: Beaches, forests,

parks, ecotourism


Biodiversity has an intrinsic

value because all species:

• Provide value beyond their economic,

scientific, and ecological contributions

• Are part of our cultural and spiritual

heritage

• Are valuable simply for their beauty

and individuality

• Have a right to exist on this planet


• Biodiversity is important to science

because it helps us understand how

life evolved and continues to evolve. It

also provides an understanding on

how ecosystems work and how we can

help maintain them for our own

benefit.

Names and word definitions of food chain

• Producers. Organisms, such as plants, that produce their own food are called autotrophs. The autotrophs, as mentioned before, convert inorganic compounds into organic compounds. They are called producers because all of the species of the ecosystem depend on them.

• Consumers. All the organisms that can not make their own food (and need producers) are called heterotrophs. In an ecosystem heterotrophs are called consumers because they depend on others. They obtain food by eating other organisms.

• Consumers i.e. :

Herbivores are those that eat only plants or plant products.

Carnivores, on the other hand, are those that eat only other animals.

Omnivores are the last type and eat both plants (acting a primary consumers) and meat (acting as secondary or tertiary consumers).

• Trophic level. The last word that is worth mentioning in this section is trophic level, which corresponds to the different levels or steps in the food chain. In other words, the producers, the consumers, and the decomposers are the main trophic levels.

FOOD WEB

The concept of food chain looks very simple, but in reality it is more complex.

How many different animals eat grass?

How many different foods does the hawk eat?

One doesn't find simple independent food chains in an ecosystem, but many interdependent and complex food chains that look more like a web and are therefore called food webs.

A food web that shows the energy transformations in an ecosystem looks like

One way to calculate the energy transfer is

by measuring or sizing the energy at one

trophic level and then at the next.

Calorie is a unit of measure used for energy

The energy transfer from one trophic level

to the next is about 10%. For example, if

there are 10,000 calories at one level, only

1,000 are transferred to the next.

This 10% energy and material transfer rule

can be illustrate with an ecological

pyramid

QIUZ IQIUZ I

1. Apa pengertian Ekologi?

2. Sebutkan struktur dan fungsi ekosistem?

3. Apa pengertian Keanekaragamanhayati?

4. Sebutkan dan jelaskan level kehati?

5. Kenapa kehati itu penting?

BIOGEOKIMIA

SuccessionSuccession

Komunitas yang terdiri dari berbagai populasi

bersifat dinamis dalam interaksinya yang berarti

dalam ekosistem mengalami perubahan

sepanjang masa. Perkembangan ekosistem

menuju kedewasaan dan keseimbangan dikenal

sebagai suksesi ekologis atau suksesi.

Suksesi terjadi sebagai akibat dari modifikasi

lingkungan fisik dalam komunitas atau

ekosistem. Proses suksesi berakhir dengan

sebuah komunitas atau ekosistem klimaks atau

telah tercapai keadaan seimbang (homeostatis).

Succession Succession

A directional, cumulative change in the species that occupy a given area, through time.

�Primary vs secondary

�Autogenic vs allogenic

�Progressive vs retrogressive

�Cyclic vs directional

Primary successionPrimary succession

the establishment of plants on the establishment of plants on

land not previously vegetated land not previously vegetated

(volcanic explosion)(volcanic explosion)

Secondary successionSecondary succession

The invasion of land that has been The invasion of land that has been

previously vegetated (fire, logging or previously vegetated (fire, logging or

cultivation)cultivation)

Autogenic successionAutogenic succession

both the environment and the community both the environment and the community

change and this metamorphosis is due to change and this metamorphosis is due to

the activities of the organism themselves the activities of the organism themselves

(environmental stress adapted)(environmental stress adapted)

AllogenicAllogenic successionsuccession

Due to major environmental change Due to major environmental change

beyond the control of the indigenous beyond the control of the indigenous

organisms organisms

((EnvEnv. Change Changes the pattern of . Change Changes the pattern of

vegetation)vegetation)

Progressive successionProgressive succession

lead process that the communities with lead process that the communities with

greater and greater complexity and greater and greater complexity and

biomassbiomass

Retrogressive successionRetrogressive succession

Lead process that the community toward Lead process that the community toward

simpler (fewer species) simpler (fewer species)

Cyclic successionCyclic succession

very local scalevery local scale

climax community new coloniesclimax community new colonies

Directional successionDirectional succession

Characterized by an accumulation of Characterized by an accumulation of

changes that leads to communitychanges that leads to community--wide wide

changeschanges

CROP ECOLOGYCROP ECOLOGY

EKOLOGI: ilmu yang mempelajari

hubungan timbal balik antara faktor

biotik dan abiotik.

Scope: Distribution and Abundance

EKOLOGI TANAMAN: pengembangan dari

ekologi dalam lingkup tanaman

(budidaya pertanian).

PerananPeranan EkologiEkologi Tanaman/pertanianTanaman/pertanian

Peranan Informative: memberikan informasi

ilmiah mengenai lingkungan hidup tanaman

yang diperlukan untuk meningkatkan dan

mengembangkan teknik budidaya tanaman

yang lebih baik

Peranan Explanative: memberikan penjelasan

ilmiah tentang gejala pertumbuhan dan hasil

tanaman yang berkaitan dengan faktor

lingkungan.

Peranan Inovative: menemukan prinsip atau

teori baru yang berkaitan dengan timbal balik

antara lingkungan – tanaman.

PerananPeranan EkologiEkologi Tanaman/pertanianTanaman/pertanian

Peranan Predictive: meramalkan pertumbuhan

dan hasil tanaman pada waktu yang akan

datang mendasarkan pada analisis terhadap

sifat tanaman dan data lingkungan.

Peranan Applicative: memberikan landasan

ilmiah bagi tindakan budidaya tanaman yang

berkaitan dengak lingkungan hidup.

Changes in Agriculture in a given Changes in Agriculture in a given

periodperiod

1. Higher Yields

2. Higher annual variability (lower stability) in

yield (due to genetic uniformity of crops?)

3. Lower Crop Diversity (increased monoculture,

less rotation, less intercropping, etc.)

4. Higher Applications of Fertilizers

5. Higher Applications of Pesticides (incl.

Insecticides, herbicides, fungicides, etc.)

6. Improved Seeds (higher harvest index)

7. More Energy Intensive

8. Increased Soil Erosion

Changes in Agriculture in a given Changes in Agriculture in a given

periodperiod

9. Decreased Soil Fertility (loss of organic matter, nutrient depletion)

10. Increased Nitrate Leaching

11. Less Effective Pest Control

12. Less Labor Intensive

13. More Subsidized

14. Less Profitable

15. Higher Risks

16. Fewer and Larger Farms (Greater inequity in land ownership)

Goals of AgroGoals of Agro--ecosystem ecosystem

ManagementManagement

• Provide an adequate income to

the farmer

• Maintain the resource base on

which future production depends

• Produce enough food to meet the

demands (of the farm family, local

community, region or nation, or

globe)

Provide an adequate income to the farmerProvide an adequate income to the farmer

"Agriculture" in the broad sense includes 3 or 4 linked enterprises:

• Input suppliers (seeds), chemicals, machinery)

• Producers (farmers/growers)

• Processors (flour mills, oilseed extraction plants, coffee roasters, etc.)

• Marketers

When production exceeds demand, crop prices are low-often lower than the costs of production.

Many countries of the world have policies that provide subsidies to growers to maintain farm income during periods of low crop prices. (Subsidies may also be designed to promote exports.)

Maintain the resource base on which future Maintain the resource base on which future

production dependsproduction depends

• Maintaining the resource base (soils,

biodiversity) is the core of most definitions of

sustainability.

• Definitions of Sustainablity by The American

Society of Agronomy: "A sustainable

agriculture is one that, over the long term, (i)

enhances environmental quality and the

resource base on which agriculture depends,

(ii) provides for human fiber and food needs,

(iii) is economically viable, and (iv) enhances

the quality of life for farmers and society as a

whole."

Produce enough food to meet the demandsProduce enough food to meet the demands

We will discuss Food Demand through an analysis of World Food Production (FAO Data)

Questions:

• What are the trends in crop yields?

• What are the global patterns in food production?

• How much food will be needed to feed the world at any point in the near future?

Need to consider:

• Population

• Arable Land

• Yields (Productivity, expressed as biomass per unit land per unit time, usually kg ha-1 y-1)

These lead to estimates of:

• Production = Land x Yield

• Per Capita Food Availability = Production ÷ population

Strategies for meeting future food Strategies for meeting future food

demanddemand

L. T. Evans (1998), "Feeding the 10 Billion":

• increase the area of land under cultivation

• increase in yield per hectare per crop [will have to be the main route]

• increase in the number of crops per hectare per year [requires irrigation, fertilizer, short-season varieties]

• displacement of lower yielding crops by higher yielding ones [reduced diversity could have ecological costs]

• reduction of post-harvest losses

• reduced use of crops as feed for animals

The crop's The crop's environmentenvironment can be can be

broken down as follows:broken down as follows:

• Environmental conditions which control

resource uptake; these may be either

– Abiotic (e.g., weather, certain soil

characteristics)

– Biotic (e.g., weeds, pests, pathogens, soil

organisms)

• Consumable resources (CO2, light, water,

nutrients)

Environmental conditions to refer to the

things, both abiotic and biotic, that

influence the rates and efficiencies at

which plants capture (or lose) supplies of

these resources.

Resources to refer to the things plants

consume in their growth and reproduction,

and

ResourcesResources

It is axiomatic that crop plants must consume resources to grow and produce a harvestable yield.

In most agro-ecosystems, crop productivity is limited by the availability of one or more required resources, most often nutrients, water, and light.

The amount of yield achieved by a crop is a function of both the level of limiting resources available to the crop, and the efficiency with which it uses these resources.

Environmental factorsEnvironmental factors

I. CLIMATE

Important features of climate include:

• light

• temperature

• humidity

• precipitation

• Wind

Climate includes both:

• Resources [light, precipitation (actually, soil water is the resource)]

• Conditions (e.g., temperature, day length, humidity, wind)


II. SOILS

1. SOIL CONSTITUENTS

2. MINERAL (INORGANIC) FRACTION

3. SOIL ORGANIC MATTER

4. SOIL STRUCTURE

5. SOIL TYPES

6. SOIL ORGANISMS

7. SOIL pH


III. RESOURCES

• Light

• Carbon dioxide

• Water

• Nutrient

CLIMATECLIMATE

I. LIGHT (Solar Radiation)

• The seasonal distribution of light is

controlled by latitude. [How does the

light environment of tropical latitudes

differ from that of temperate and boreal

latitudes?]

• Plants (including many crops) show

photoperiodic responses to day length,

particularly in their phenology.

CLIMATECLIMATE

I. LIGHT (Solar Radiation)

• Phenology has been defined as "the

sequence of development events during

the plant's life cycle as it is determined

by environmental conditions" (Hall,

2001); these include flowering, bolting,

tuber formation, etc.

• "Long day" (LD) plants; "short-day" (SD)

plants; and "day neutral" (DN).

CLIMATECLIMATE

II. TEMPERATURE

The seasonal and diurnal variation in

temperature increase with latitude

Temperature also decreases with increasing

altitude

The rate of temperature change with altitude

is called the lapse rate and is about 1 0C

100 m-1 for dry air and about 0.6 0C 100

m-1 for wet air.

CLIMATECLIMATE

II. TEMPERATURE

• Most plant processes have an optimumtemperature.

• Respiration increases with increasing temperature.

• Plant development is mostly controlled by temperature. Plants sense environmental temperature in terms of degree days --the cumulative number of the degrees above a base or threshold temperature.

• Crop plants exposed to higher than normal temperatures develop at a more rapid rate (for example, flower earlier), which could decreaseyield.

CLIMATECLIMATE

III. PRECIPITATION

GO TO ANOTHER SLIDE :

RAINFALL N CROPPING SYSTEMS IN

INDONESIA…Ю

SOILSSOILS

I. SOIL CONSTITUENTS

• Atmosphere

• Water

• Mineral (inorganic) materials

• Soil organic matter (SOM)

• Soil organisms

The atmosphere below ground in the soil difference substantially from that aboveground. The soil atmosphere is higher in CO2 and lower in O2

SOILSSOILS

Soil provide an important environment for plants/crops due to:

1. Plants need anchorage, so that there should be adequate soil layer.

2. Plants need water, so that soil should hold adequate water and supply.

3. Plants need oxygen for respiration, so that soil should be able to provide it without any interruption.

4. Plant roots release CO2 during respiration, and soil should be able to regulate the movement of this gas without allowing it to build up to toxic levels

SOILSSOILS

5. Plants need nutrients from soils, which are

absorbed by roots, so that soils should

have some characteristics to supply and

retain nutrients.

6. Plants add a lot of dead material (OM) and

the soil should have able break them to

some form so that they will not interfere

with plants and their root systems.

7. Some plants through root exudates add to

soil toxic chemicals (allelo-chemicals) and

soil should be able to decompose them to

avoid root damage.

SOILSSOILS

8. During heavy rainy periods, large

volumes of water are added with a

very high intensities and the soil

should be able to handle these

volumes without severe soil losses

9. There are toxic gases released when

animal and root systems grow in

soils and soil should be able to either

release these gases to atmosphere or

convert to non-toxic form by other

reaction

SOILSSOILS

10.When both plant and animals live in

soil, it should be able to maintain

suitable temperatures required by

those living beings

SOILSSOILS

Therefore…

Soils is suitable for everything at anytime

It is required to treat the soil with the right knowledge of it in order to receive benefits the mankind wants

soil always have many associations and interactions among these factors (physical, chemical, physico-chemical and biological factors)

Physical factorsPhysical factors

Soil texture

Particle size distribution (clay, silt and

sand)

In general

Coarse sand 0.25 – 2.0 mm

Find sand 0.05 – 0.2 mm

Silt 0.002 – 0.05 mm

Clay < 0.002 mm


Bulk density and porosity

Both factors related to:

1. Capacity for gas exchange

2. Root growth and penetration

3. Drainage and retain water

4. Infiltration and percolation


Soil structure

Composition of pores and soil

aggregates

Pores consist of :

Micro pores (capillary water retained)

Macro pores (gas exchange and

drainage)

Crumb structure – best for agriculture

50 % each of micro and macro pores.


Soil water content

• Saturated condition

• Field capacity

• Permanent wilting point

Soil temperature

• Increase root growth and activities

• Increase microbial population

• Increase organic matter decomposition

• Increase seed germination

Chemical factorsChemical factors

Nutrient contents in soil

Gas content

Chemical reactions

Physico-chemical factors

(good for agriculture)

pH (6 – 7)

CEC (Cation exchange capacity) (> 40 mg/100

g soil)

EC (electrical conductivity) = water quality

parameter (0.4 – 0.7 m mhos/cm)

Biological factorsBiological factors

Micro and macro both fauna and flora

Important activities:

• Mineralization of organic matter

• Nitrogen fixation in legumes

• Micorrhyza promoting P absorption

• Enzymes activities and nutrient transformation in soils

• Improve porosity by earthworm (tunneling)

• Improve root absorption activities

RESOURCESRESOURCES

Light

Quantity

• Full Sunlight: 200-500 Wm-2 or 1000-2000 µmol m-2 s-1 (W = J s-1)

• Cloudy sky: 20-90 Wm-2 or 100-400 µmol m-2 s-1

• Seasonality: The highest monthly (i.e., growing season) maximum light levels are at higher latitudes.

Crop yields in the tropics (compared to temperate zones) are ultimately limited by:

• incident radiation

• cloudiness-compare wet season and dry season yields

RESOURCESRESOURCES

Growth and Yield are ultimately related to light interception.

• At the leaf level: There is a minimum amount of light required for a positive netphotosynthesis to occur, called the light compensation point.

• At the canopy level: Some leaves in a canopy will be shaded by other leaves, some below, and perhaps some below the light compensation point.

• Rates of canopy photosynthesis are usually proportional to LAI

RESOURCESRESOURCES

• At the crop level: Crop growth (and

yield) is generally a function of leaf-

area duration (LAD), the area under a

curve of LAI vs. time.

• LAD is proportional to the total

amount of light energy absorbed

during the crop's growing season,

and thus to yield.

RESOURCESRESOURCES

CO2

The direct (physiological) effects of this increase in atmospheric CO2 are:

• increased rates of photosynthesis, especially in C3 plants, resulting in higher crop yields.

• increased water-use efficiency.

• higher C:N ratios in plant biomass.

• Higher CO2 concentrations induce partial closing of the stomates, which increases the resistance to the flow of water vapor, reducing transpiration and thus increasing water-use efficiency.

RESOURCESRESOURCES

• Higher leaf temperatures (caused by

stomatal closure) associated with

increased [CO2] can lead to increased leaf

turnover rate (higher leaf temperatures

and more rapid leaf aging),

• Decreased specific leaf area, reducing the

CO2-fertilization effect.

RESOURCESRESOURCES

Soil Water

• Field capacity is the amount of water held

in a saturated soil after all excess water

has drained off; the water potential at field

capacity is -0.1 to -0.2 MPa.

• Permanent wilting point is the point at

which a (particular) plant can no longer

absorb water from the soil, for most plants

in most soils the water potential at the

permanent wilting point is about -1.5 MPa.

RESOURCESRESOURCES

• Available water is the amount of water between field capacity and permanent wilting point.

• Soil water content is influenced by both soil texture and soil organic matter (SOM).

• Fine-textured soils have a higher total pore volume, and hence can hold more water.

• Clay particles hold water more tightly. SOM functions similar to clay particles in affecting soil water-holding capacity and soil water potential.

RESOURCESRESOURCES

Nutrition

• Macronutrients, those required in rather high amounts by plants, are nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S). Most fertilizers contain N, P, and/or K.

• Micronutrients are elements that are also essential for growth but are required in lower amounts; these include iron (Fe), copper (Cu), zinc (Zn), boron (Bo), molybdenum (Mo), manganese (Mn), cobalt (Co), and chlorine (Cl).

Nutrient cyclingNutrient cycling

Refers to the processes that transfer nutrients to and from plants and the various soil (and atmospheric) pools.

These pools can be characterized as:

• active, inorganic forms and microbial biomass-very rapid turnover;

• slow, new crop residues and coarse particulate organic matter; and

• Passive, fine particulate organic matter and humic substances-very slow turnover.

Interactions between Resources and Interactions between Resources and Environmental FactorsEnvironmental Factors

Crop yield is a function of resource use. In general, resource-use efficiencies are the products of resource uptake (capture) and resource utilization (biomass or yield produced per unit of resource captured) (Janssen, 1998).

That is the relationship between yield (Y) and resource supply (S) involves resource uptake (U):

• Y/S = U/S (resource uptake) × Y/U (resource utilization efficiency)

• Y/U is the physiological RUE, whereas U/S is the ecological RUE.

Factors that influence crop yield are of Factors that influence crop yield are of several types and include:several types and include:

• Resources not under grower control: light, CO2, water (precipitation), nutrients released by mineralization.

• Environmental conditions, not under grower control: temperature, wind, seasonality, topography, length of growing season, relative humidity; soil type, soil depth, SOM, soil pH; pest, weed and pathogen populations (in part).

• Resources under grower control: nutrients (from fertilizer), water (from irrigation).

Factors that influence crop yield are of Factors that influence crop yield are of several types and include:several types and include:

• Environmental conditions under partial grower control: pest, weed, and pathogen populations; SOM; soil structure; soil pH.

• Crop varieties.• Management: land preparation, choice of

cropping system; choice of cultivars; date of planting; plant population; timing of nutrient input; timing of pest, weed and pathogen control; date of harvest; management of residues.

• Infrastructural or institutional factors: access to credit, suitable varieties, extension services, inputs, markets.

Interactions Among Species in Interactions Among Species in

AgroecosystemsAgroecosystems

This part of the course considers some of

the other organisms, in addition to crops

and soil organisms, that occur in

agroecosystems, particular herbivores

(mostly insects) and their predators, and

competitors (weeds). Pathogens are

discussed only briefly.

HerbivoresHerbivores

• Why don't insects (and other herbivores)

consume all available plant biomass? That is,

Why is the world green?-most likely answers are

plant defenses that limit which herbivores can

feed on which plants, and predators that keep

herbivore populations in check.

Groups of herbivores:

• Vertebrates-birds, mammals

• Invertebrates-insects, arachnids (mites),

mollusks (snails, slugs). Of these groups insects

cause the greatest crop losses in most

agroecosystems.

HerbivoresHerbivores

Plant Strategies to cope with herbivory:

• Escape-short life cycle

• Tolerance--Compensation for tissue loss

• Defense--protection of tissues

Ecological problems associated with insecticide

use:

1. Insecticide resistance

2. Pest Resurgence

3. Secondary Pest Outbreaks

Integrated Pest Management (IPM).

Competitors (Weeds)Competitors (Weeds)

Characteristics of Weeds

• High seed production, competitiveness,

low attractiveness, seed longevity, seed

dormancy, rapid emergence.

• Most weeds evolved from early

successional species; many are crop

relatives

Competition/Competition/NicheNiche TheoryTheory

Two species can occupy the same habitat and

not compete if:

• The species use different resources. This is

often true for animals, but seldom true for

plants.

• Resources are sufficient for both. For

example, plants in the desert seldom compete

for light.

• The species obtain their resources from

different parts of the habitat. I.e., the species

have a somewhat different niche with respect

to resource acquisition.

Competition/Competition/NicheNiche TheoryTheory

• Many plant ecologists (e.g., David

Tilman) maintain that plant species

specialize with respect to their ability

to capture different resources. This is

probably not true, however, for crops

and weeds.

Competitors (Weeds)Competitors (Weeds)

Weeds reduce crop yield by reducing the supply of resources through competition.

• Plants use common resources--Light, C02, Water, Nutrients.

• Plants obtain resources from resource depletion zones, which depend on root and shoot architecture, and on resource mobility.

• Intensity of competition depends on the degree of overlap of resource depletion zones.

PathogensPathogens

• Diseases reduce ecological resource use

efficiency by reducing resource uptake

by various mechanisms: obstructing

vascular tissues, damaging roots,

restricting root growth, or removing leaf

area.

• Plants possess morphological and

chemical defenses against pathogens:

PathogensPathogens

• Morphological-- cuticle

• Chemical-- both constitutive and

inducible (inducible defenses against

pathogens are called phytoalexins)

• These defenses most effective for

aboveground pathogens.

The Functional Role of Diversity in The Functional Role of Diversity in

AgroecosystemsAgroecosystems

Diversification is the Key to sustainability, according to most agroecologists.

Diversity in cropping systems:

Monoculture:

• Continuous

• Crop Rotation-short rotations vs. long rotations

Polyculture:

• Intercropping

• Agroforestry

• Home-garden systems

Diversity has been defined as:

• Richness-number of species

• Equitability-number and relative abundance

• Connectance or complexity-usually as food-web complexity

Ecosystem function is usually defined in terms:

• energy capture (i.e., productivity-yield inagriculture)

• nutrient cycling

• population regulation (including food web structure)

• stability

Crop RotationCrop Rotation

Prior to development of agrichemicals,

rotations were the standard practice

to control pests and diseases and

maintain soil fertility.

Development of pesticides and

herbicides made continuous

monoculture possible. Thus

continuous monoculture is a relatively

recent agricultural practice.


Short rotations vs Long (Extended) Rotations:

Short rotation:

• Usually just 2 years

• Objective is typically pest control

• Corn-soybean is the commonest crop system in the US-both crops have a high demand

Long (extended) rotations:

• 3 years or longer

• Objectives are pest control, maintain soil organic matter, reduce agrichemical inputs

• Usually includes hay, pasture, or "green manure" to improve soil fertility.


Rotation Effect!

This term refers generally to the higher yields of most crops when grown in rotation, and more specifically to the yield increases that cannot be compensated for by input substitutions.

Most crops produce higher yields in rotation than in continuous cultivation, usually 10-15% higher in maize (Singer & Cox, 1998).

IntercroppingIntercropping

• Intercropping involves growing two crops in the same field at the same time. The following are different ways of intercropping, in order of increasing degree of association between crop components:

• Relay-intercropping-planting a second crop before harvesting the first crop.

Continue…


• Strip-intercropping-growing 2 or more

crops in alternating strips. Smith &

Carter (1997) found that maize grown

in a strip intercrop with alfalfa

produced yields 6% higher in 40-ft

wide strips, 11% higher in 20-ft wide

strips, and 17% higher in 10-ft wide

strips. May be due to extra light in

border rows of maize.

Continue…


• Between-row intercropping -growing 2 or

more crops in alternating rows.

• Within-row intercropping -growing 2 or

more crops in the same rows.

• Between-row and within-row intercrops

may be either additive or replacement

designs.

Intercropping Concepts.Intercropping Concepts.

• Additive vs. replacement intercrops. In an

additive intercrop both species are planted

at the same density as in their respective

monoculture; in a replacement intercrop a

row of one crop "replaces" a row of the

second crop in forming the intercrop.

Additive intercrops double the density, and

therefore may use resources more

completely.


Duration refers to the temporal overlap of the intercrop components:

• Differing duration-usually combines a short season crop and a long season crop. Intercrops of differing duration are usually additive.

• Similar duration-competition more intense because both components are using resources at the same time. Intercrops of similar duration tend to be replacement types.


• Dominant vs. subordinate components.

Typically, one crop component of the

intercrop is more competitive and hence

dominates the mixture in terms of growth

and yield.

Dominance may be due to:

• Rapid initial growth

• Height

• Photosynthetic pathway (C4 crops tend to

be dominant when grown with C3 crops)

• Legumes are usually subordinate

Measuring Intercrop PerformanceMeasuring Intercrop Performance

• The performance of intercrops relative

to monocultures of the component

crops is usually measured as Land-

equivalent ratios (LER) or relative yield

totals (RYT):

• Relative Yield (RY) = Yield in

intercrop/Yield in monoculture

• LER = RYT = Y(i)/Y(m) = RY(1) + RY(2)

+ RY(3) + ....

Measuring Intercrop PerformanceMeasuring Intercrop Performance

• When LER or RYT > 1, the intercrop is

said to show overyielding. That is, the

intercrops are more productive than

the monocultures of the components

crops.

• The RYs of dominant components are

often close to 1.0; efforts to increase

intercrop performance often center on

increasing the RY of the subordinate

component.

Global Change and AgricultureGlobal Change and Agriculture

Global warming

Evidence of global warming:

• Temperature records-most of the increase has been in night temperature

• Retreat of glaciers; decreased snow and ice cover

• Measurable rise in sea level

• Increased heat content of oceans

• Increased plant growth (Myneni et al. 1997)


The latter include:

• Increased values of NDVI (normalized difference vegetation index) detected by remote sensing

• Increased biomass deposition in European forests

• Increased recent tree-ring growth in Mongolia

• Upward migration of plants on European mountain tops


• The increase in plant growth is likely due

to longer growing seasons; high latitude

winter temperatures increased up to 4 C in

the winter.

• Nicholls (1997) attributes 30-50% of the

increased wheat yield in Australia since

1952 to decreased frequency of frost.


Presumed causes of global warming:

• Greenhouse gases-CO2, CH4, N20 (nitrous oxide), CFCs (chloroflurocarbons)

• Land-use changes.

• Deforestation

• Increased fire frequency

That greenhouse gases have caused global warming as not been "proved", there are still valid disagreements.


Robinson et al. (1998, unpublished paper privately distributed) dispute that any global warming has occurred in response to increased CO2.

It is accurate to say that there is currently a strong concensus among scientists that changes in atmospheric chemistry are affecting climate in predictable and understandable ways.


Effects of [CO2] on Plant Growth

• Gross photosynthesis increases and photorespiration decreases.

• Stomatal resistance increases (stomatesclose partially in response to increased [CO2]), transpiration therefore decreases, and water-use efficiency increases (since stomatal closure affects transpiration rates more than CO2 uptake rates).

• C3 vs C4 plants: Growth of C3 plants would be enhanced more than that of C4 plants


Interactions need to be considered:

• [CO2] and other resources. For example, if

N is limiting, increased [CO2] may not

increase crop growth.

• [CO2] and environmental influences

(especially temperature).


Affects of Global Change on Agriculture

• The overwhelming evidence from (short term) experiments with increased [CO2] (either greenhouse or FACE-free atmosphere carbon dioxide enrichment-studies) is that biomass and/or seed production increases with increasing [CO2].

Continue…


• These studies are almost always done with (1) no temperature increase, and (2) optimum levels of other resources, especially N and water.

• [One interesting conclusion we might draw is that much of the crop yields experienced in the past 50 years must be due to increased [CO2] and not just breeding and improved management, as usually assumed.]

Example of case

Pengelolaan agroekosistem

PolaPola BudidayaBudidaya

Tahap subsisten

Pada tahap ini petani mengusahakan lahan

pertanian untuk memenuhi kebutuhan

hidupnya dan kaum kerabatnya.

Masukan seperti yang dilakukan pada

pertanian modern belum dikenal, belum

ada penggunaan bahan kimiawi sintetik.

Umumnya produktivitas rendah, dan

petani mengerjakan tanah garapannya

dengan mengikuti irama musim dan

daur alami.


Tahap eksploitasi

Segala usaha diarahkan untuk mencapainilai ekonomis terbaik atau tertinggi. Input atau masukan baik berupa saranaproduksi atau masukan lainnyadiusahakan tidak hanya optimal, kadang-kadang bahkan maksimal.

Penggunaan teknologi amat intensif, bahankimia pertanian amat diutamakan. Efisiensi juga diusahakan denganmengatur daur bertanam dan perlakuanmengikuti kalender dan rutinitasmanusia, karenanya


Tahap eksploitasi

Pertimbangan kondisi alami di

pertanaman sering tidak

diperhatikan. Pada awalnya usaha

seperti ini memang memberikan

hasil yang baik, sehingga petani

atau penanam semakin dirangsang

untuk terus menggunakan sarana-

prasarana produksi berbasis

teknologi tinggi.


Tahap kritis

Tahap eksploitasi yang tidak memperhatikan

watak dan sifat ekologis lingkungan pertanian

mengakibatkan kemunduran usaha karena

beban yang ditanggung agroekosistem tidak

seimbang.

Waktu yang diberikan agar lingkungan pulih

terlebih dahulu dan mampu memberikan daya

dukung yang tepat tidak terpenuhi. Sebagai

gantinya masukan teknologi dianggap pasti

mampu memberikan dukungan terhadap

proses produksi, dan kemudian dipergunakan

sebanyak-banyaknya.


Tahap kritisYang selanjutnya terjadi adalah tidakimbangnya agroekosistem, sehingga biayausaha tani tidak akan dapat menghasilkanlaba. Sebaliknya, biaya menjadi terlalubesar tetapi produk hanya sedikit, sertaharganya bisa jatuh karena kualitasnyajelek/tidak disukai konsumen karenamengandung residu bahan kimiapertanian.


Tahap bencana

• Apabila tahap kritis tidak diantisipasi

dengan baik, maka tahap berikutnya

yang terjadi adalah bencana. Modal

usaha tani tidak akan mendatangkan

keuntungan, biaya yang dikeluarkan

besar tetapi usaha yang dijalankan tidak

mampu mengembalikan modal.


Tahap bencana

• Usaha tani mengalami kebangkrutan, sedang lingkungan pertaniannya menjadirusak karena terlampau dieksploitasi.

• Lebih parah lagi, kepercayaan konsumenmungkin juga akan hilang, sehingga tidakada alternatif lain kecuali menutup usaha; atau memulai lagi dari awal denganmemperhatikan kaidah-kaidah ekosistemdan menjaga lingkungan pertanaman agar lebih berlanjut/lestari/"sustainable". Kondisi ini tidak mungkin dilanjutkandengan teknik dan metode pertanamanyang sama dengan sebelumnya.


Tahap pertanian ekologis/organik/sustainable

• Jika petani/penanam ingin keluar dari

bencana yang menimpa usaha taninya, maka

harus dilakukan perubahan metode dalam

penyelenggaraan budidaya tanamannya.

• Penerapan metode yang lebih akrab lingkungan

seperti misalnya model PHT (Pengelolaan Hama

Terpadu), pertanian organik, sistem tumpang

gilir atau tumpang sari, budidaya lorong,

sistem surjan dan berbagai cara bercocok

tanam lainnya harus dan perlu dilakukan.


Tahap pertanian ekologis/organik/sustainable

• Cara bercocok tanam itu haruslah

merupakan cara yang lebih mengabaikan

sifat dan watak tanamannya, menjaga

kelestarian media tanam, berorientasi

pada produk berkualitas (dalam arti

kandungan bahan bebas residu dan sisa

bahan kimia pertanian yang

membahayakan kesehatan).

CROP ECOLOGY