© T. M. Whitmore TODAY • Questions about agricultural change theory? • Today: Classifying Agriculture Long fallow (swidden) agriculture Wet rice agriculture
Jan 18, 2016
© 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
© T. M. Whitmore
© T. M. Whitmore
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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© T. M. Whitmore
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
© T. M. Whitmore
© T. M. Whitmore
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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© B.L. Turner
© B.L. Turner
© B.L. Turner
© B.L. Turner
© T. M. Whitmore
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
© T. M. Whitmore
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
© T. M. Whitmore
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”
© T. M. Whitmore
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
© T. M. Whitmore
© T. M. Whitmore
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
© T. M. Whitmore
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
© T. M. Whitmore
© T. M. Whitmore
© M. Meade
© M. Meade
© T. M. Whitmore
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
© T. M. Whitmore
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
© T. M. Whitmore
© M. Meade
© T. M. Whitmore
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
© M. Meade
© T. M. Whitmore
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)
© M. Meade
© M. Meade
© M. Meade
© M. Meade
© T. M. Whitmore
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
Nitrogen
Yie
ld
Indica
Japonica
© M. Meade
Upland (rain-fed) rice in Volta
Upland (rain-fed) rice in India