© t. m. whitmore today questions about agricultural change theory? today: classifying agriculture ...

© T. M. Whitmore

TODAY•Questions about agricultural change

theory?

•Today: Classifying AgricultureLong fallow (swidden) agricultureWet rice agriculture

© T. M. Whitmore

Classifying Agriculture – a series of ways to view

agriculture expressed as continua

•Production Goals

•Production Means/Technology

•Social-cultural traits

•Output intensity (e.g., kg/ha/yr)

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Production Goals• Consumption/Subsistence

Main goal is family food production Risk aversion Goal is optimum output (family

survival)• Market/Commodity

Food sold and processed/consumed away from farm (family food is purchased) Main goal is profit (innovation and

change frequently) Goal is max output per unit of land,

labor, and cost

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Production Means/Technology

• Paleo-technic (traditional)Origin/Type of inputsServicesDiversity of crops

• Neo-technic (with fossil fuels)Origin/Type of inputsServicesCrop specialization

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Social-cultural Continuum I•Traditional

Customs and rulesLand tenureInstitutional frameworks“Smallholder” agriculture

PovertyField fragmentationRisk aversePolyculture & intraspecies diversity

Role of off-farm income

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Social-cultural II

•Modern/CommercialCustoms and rulesLand tenureInstitutional frameworks

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Output intensity

•TraditionalUsually lower per area / yr May also be low per labor unit but

not always

•CommercialHigh per labor unitUsually high per area

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Paleo-technic/Consumption agriculture

•Long-fallow cultivation AKA

swidden slash and burnshifting; or brush/forest fallow)

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Long-fallow (swidden) cultivation

•Main properties

•Geography

•Ecology of swidden systems

•Swidden process details

•Nutrient cycling

•Problems

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SwiddenLabor, population, & intensity

issues• Tenure - mostly some sort of common

tenure; but changing

• Shifting does not encourage freehold; families typically have multiple fields at any instant (in different stages of use/fallow)

• Labor demands are minimal compared to more intensive ag

• Rapidly changing – little true swidden still practiced (in terms of numbers of people – still lots of land)

• Role of pop growth

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Main properties• Fields shift (rotate) not crops• Period of non-use (fallow) much greater

than period of use• Use of “slash and burn” for clearing and

burning• Often intercropping – but not always• Very simple technology – often no plow• Low use of neo-technic inputs (chemicals,

machinery, etc)• Used in areas of low population density

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Geography

• LA - Amazonia and parts of C America

• SE Asia

• Equatorial and tropical Africa

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Ecology of swidden systems

• Vegetation: there is a great irony here; very poor soils in most areas of swidden yet much of it supports forest! What’s up?

• Equatorial rain forests: richest biome on earth;

• Wet-dry tropical vegetation: open forests or savannas

• Swidden not nearly as practical outside heavy tropical forests

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Swidden process details• Forest is felled, brush spread, and burned

• Burning deposits a layer of ash

• Fields planted directly in the ash layer

• Farmers typically have multiple fields in stages of fallow

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Nutrient storage & cycling• Very large quantities available in biomass

• Non-primary forest (~ 8-10 yrs fallow) ~ 200-400 tons/ha of dry matter~ 500 kg each of N, K, Ca, Mg, lots of S and P

• Note that a moderately good soil (e.g., alfisol) 2.5x the N of the forest biomass; ~ equal Ca and Mg 75% of biomass’ total Kbut only 9% of the phosphate P

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Slash and burn converts biomass to fertilizing ash

• Biomass pre burn ~ 200-400 tons/ha

• Typical burn is low intensity (600º C on surface but < 70-150º C at 2 cm depth)

• Typical ash layer = 4 tons/ha (including charred wood) so a lot is lost to smoke

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Slash and burn converts biomass to ash – much is lost

• Typical ash layer => increased nutrients BUT down sharply over time70 kg N per ha – but down sharply over time14 kg P per ha – but down sharply over time45 kg K per ha – but down sharply over time increased Ca and Mg – but down sharply over

time increased pH – but down sharply over timedecreased Al as it is replaced by exchangeable

bases – but it increases over timeoverall increased fertility - temporarilygain is greatest on poor soils but fall back is

faster there as well

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Problems I• First crop benefits most from a burn

• 2nd crop less so

• ~ 2x exchangeable bases after a burn than before (in poor soils)

• Ash is quickly carried away by rains

• Fertility boost lasts only 1-3 years and then yields drop very rapidly

• Loss of fertility and invasion of pests and weeds makes it easier for farmer to move to another plot and repeat the process

• hence “shifting cultivation”

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Problems II• If the original plot is fallowed long enough to

recover its original forest growth (20+ years in many areas) all is OK

• Thus, to be able to use 1 ha for crops, a farmer must have access to more than 20 ha to allow for this movement and fallowing

• If this area is not available and farmer returns to previous plot early the forest is less well developed, the burn creates less ash, fertility gain is less ... ultimately can damage soil structure

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Traditional Asian Rice Agriculture• Small holders

• Paddy and upland• Family labor mostly• About 1/2-1/2 subsistence/market• Large yields (high per ha but low per capita)

support high populations and high densities• Has maintained high productivity for

millennia – among the most successful human land modifications

• Intensive ag (even before modern inputs): high labor inputs, landesque capital; high outputs

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Rice Geography

• Rice domesticated in SE Asia (native to foothills of Himalayas and hills in Indochina)

• Most area in lowland river flood plains or the broad deltas of the major rivers in SE Asia (photo)

• Some in spectacular terraces in S China and Java for example, but there are not the norm

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Wet Rice Ecology

• Requires high temps (> 20º C for 3-4 months)

• Requires lots of water (> 1000 mm during growing season)

• Wet rice needs to be submerged 100-150 mm for 3/4 of growing season

• Requires a impermeable sub soil (best on heavy soils) – but that is common in deltas etc. so often poor tropical soils can be well used for this

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The Wet in wet rice• Water in fields

Protect from rain splash erosionProtect from high tempsLimits leaching hosts weeds, fish, and insects =>

complex food ecology directed to human nutrition

• Water provides nutrientsSilt provides mineral-based nutrients Nitrogen from water plants and

nitrogen-fixing blue-green algae in the water

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Processes I• Field maintenance

Annually the bunds, dykes, and canals etc need maintenance and repair

fields need to be reduced to muddy consistency for planting or transplanting (plows and oxen)

• Transplanting about 1/10 of all land given over to

seedbed 4-5 weeks before movingWomen usually do the transplanting in

low water

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Processes II• Weeding by pushing the weeds down in the

water => composting and increasing yields

• Water level control

• Protection from pests etc.

• Harvesting, threshing, storage and milling

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Intensification in traditional wet rice• Labor: Needs in the system are large so system

can “absorb” lots of additional laborMore inputs (e.g., labor) leads to more

output – but reduced marginal improvement

Can lead to “involution”• Terraces (not the rule)• Multicropping with other crops (lessening

over time)

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The dilemma in traditional wet rice

• How can production be increased to meet increased consumption demand?All available opportunities for

extensification doneLabor already fully utilized (even

involution)Other intensification strategies already

maxed out

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The “Green Revolution” solution

• Improve rice plants to increase yields per plantJaponica vs Indica varietiesDwarfsDay lengthTime to maturity

• Plant more closely together in fields to increase per area output

• Add more inputs in the form of chemical fertilizers Fertilizer responsiveness

• Problems: as with other green revolution

Upland (rain-fed) rice in Volta

Upland (rain-fed) rice in India

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Documents

forest biomass

areas of swidden

tonshatypical burn

stages of fallow

original forest growth

ash layerfarmers

depth typical ash layer

yrs fallow