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ERS 383 > Tropical Soils > Flashcards

Tropical Soils Flashcards

1
Q

What is soil?

A
  • organic matter, minerals, atmosphere, solution(water)
  • rooting medium for plants
  • interfance between mineral and organic world
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2
Q

Primary minerals

A
  • mineralso inheateted directly form parent rock, no chemical alterations
  • quartz, feldspar, mica
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3
Q

Secondary minerals

A
  • weathered products of primary minerals
  • influence soil chem and phusical properties
  • small size but large SA
  • AL & Fe oxides, hematite, gibbsite
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4
Q

Clay

A
  • active mineral portion of soil
  • kind of clay depends on proportion of iond, silica and al in soil
  • leaching changes clay type
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5
Q

tropical soil vs temperate soils

A
  • tropical soils have lots of leaching due to rain so have different clay soils
  • tropical soils have more kaolinite , temperate has more Smecitites
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6
Q

Kaolinite

A
  • 1:1 clay mineral ratio between Si:Al
  • heavily weahered soils
  • cohesive, impermiable and sticky
  • doesnt expand apon wetting
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7
Q

Smectites

A
  • 2:1 Si:Al
  • sweelling appon wetting and cracking when drying
  • difficult ot cultivate
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8
Q

Illite (Hydrous Mica)

A
  • Minimum swelling and shrinking
  • Strongly attached to K
  • occurs in less weathered soils
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9
Q

Allophane

A
  • common in volcanic soils
  • have + or - charge depending on pH
  • strong adsorption of P
  • Amourphous
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10
Q

Sesquioxide Clay

A
  • leached silica difficent soils in warm climates
  • only AL and Fe left
  • not sticky & do not swell
  • can absorb alot
  • high adsorption of p making it less avaiable for plants
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11
Q

Soil air

A
  • oxic conditions O2,N2,CO2,N2
  • anoxic conditions CH4,H2S,NH3
  • root trspiration and micro/macro fauna respiration effect the air
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12
Q

Soil water/ solution

A
  • mobile/ liquid fractiom of soil
  • transports nutrients bwtween soils and plant roots
  • facilitates ion exchange
  • soil quality depends on, hydrology and soil nutrient concentration
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13
Q

What are soil Colloids?

A
  • any solid substance measured in microns
  • large SA used fir chem exchange, and RXNs
  • helps substances stick
  • mostly clay and humus collids
  • overall negative charge
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14
Q

Clay collids

A

morphous structure

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15
Q

Humus collids

A
  • intermediate product of highly decomposed orgo mat
  • amorphous structure
  • most stable form of orgo mat in soils
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16
Q

soil ion exchange

A
  • ions adsorbed to siol collids resist leaching
  • some ions have stronger attraction depending on thier charge
  • determined by soil fertility
  • location of exhange: collids or plant roots
  • dominated by cation or anion exchange depending on pH
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17
Q

Anion Exchange

A
  • low ph
  • ph below 5
  • soil is positvle charged
  • H+ exchanged for Fe and Al, soil accumulates Fe,Al
  • red soil, tropical
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18
Q

Cation Exchange

A
  • ph above 5
19
Q

Soil structure

A
  • arrangment of soil particles into sturctures that clump together
  • granular, blocky, platey, massive, single grain
20
Q

Soil orgo mat (SOM)

A
  • plant, animal, microbrial residue
  • soc= SOM x 1.724
  • soil backbone, glue, mositure maintaining sturcture
  • decreases erosion
  • SOM depends on orgo input
21
Q

SOM decomp rates

A

Fast decomp
- sugar, amino acids protiens
slow decomp
- lignin
- foration of humus stable for 1000’s of years

22
Q

SOM content in tropics \

A

humid tropics 2%
subhumid tropics 1%
semiarid tropics 0.5%

23
Q

Cental Amazon basin

A
  • old soils , due to lack of disturbance(glaciation volcanizm)
  • highly leached nutient poor
  • high Al and Fe []
  • high acididty
  • low cation exchange
24
Q

Central America

A
  • Young soils, vocanic origin rich in nutirents
  • high p but low availability
  • low pH
  • low cation exchange but better than old soils
25
Q

what is Laterization?

A
  • the progressive leaching of soils mobilizng Fe, Si and Al from soils to agragate lower in bhe soil coloumb
  • leaving behind a residual concentration of sesquioxides (iron and aluminum oxides) and kaolinite clay.
26
Q

How does laterization occur?

A
  • removal of vegitation
  • increases ersosion
  • repeat wetting and drying
  • Fe, AL Si leached into lower columb forming a brick like
27
Q

characterisitics of Laterite soils

A
  • found in humid tropical area old/ stable landscapes
  • low pH. Highly leached
  • extream peatheing of primary minerals
  • low in fertility
  • cannot hold water
  • high p fixation
  • low in humus
  • low cation exchange
28
Q

low rainfall and humidity

l

A

low rates of decomposition, slowing soil formation

29
Q

parent matieral high in quartz

A

difficult to break down into secondary, slowing soil formation

30
Q

High clay content

A

Aeration and water movment are poor, slowing soil formation

31
Q

steep slopes

A

high erosion and constant exposure of bedrock, sows soil formation

32
Q

High water table

A
33
Q

Continued deposition of new matieral

A

no chanve for horizon developement, solwing down soil formation

34
Q

O,A,B,C

A
  • Organic horizon
  • A mineral horizon, (roots)
  • B Transitional Zone
  • C unconsolidated rock
35
Q

Oxisols and Ultisols
(ferralsol)

A
  • deep,reddish, acidic, highly weathered
  • high Fe Al oxides, low fert, low OM
  • 36% of topics
  • humid and subtropics along with some savannas
36
Q

Alfisol(luvisol)

A
  • not unique to the tropics
  • prolonged dry seaon in tropical biomes
  • predominatly under forests
  • can be fertile but have curstin, erosion and rought strees problems
  • 13% of tropical land area
  • high in K, MG and Ca
37
Q

Entisols (regosol)

A
  • recently transported by water, young, without destinct horizon
  • highly fertile, best tropical soil for plant growth
  • dev on inert parent matieral
  • 13% of tropical lands
38
Q
A
38
Q

Inceptisol (cambisol)

A
  • young soils
  • ditincct horizon
  • very fertile
  • dev on land covered by volcanic rock
  • occupy 12% of tropical lands
39
Q

Terra Preta do Indo

A
  • black earth
  • anthropogenicly made via charcoal, manure, bones, pants and unwanted garbage
  • dark, fertile high in charcoal content
  • 450-950 AD can be upto 2m deep
  • high levels of microbial activity, low leaching
40
Q

undistured soils in the tropics

A

are productive
- loss little nutirents due to plant cover, no leaching
- nutirent accumulation through rainfall, lighting, dust , nitrogen fixers, root nutient pumps

41
Q

Conversion of virgin tropical rainforest to agricultural land

A
  • year 1: high yeild , high SOM and nutirents in soil
  • year 2: lower yeild, depletion of SOM
  • year 3: uneconomical to produce crops ,soil depelated of som and nutrients, secondary forest succession happens
42
Q
A

ERS 383 (5 decks)

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