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
2
Q
Primary minerals
A
- mineralso inheateted directly form parent rock, no chemical alterations
- quartz, feldspar, mica
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
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
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
6
Q
Kaolinite
A
- 1:1 clay mineral ratio between Si:Al
- heavily weahered soils
- cohesive, impermiable and sticky
- doesnt expand apon wetting
7
Q
Smectites
A
- 2:1 Si:Al
- sweelling appon wetting and cracking when drying
- difficult ot cultivate
8
Q
Illite (Hydrous Mica)
A
- Minimum swelling and shrinking
- Strongly attached to K
- occurs in less weathered soils
9
Q
Allophane
A
- common in volcanic soils
- have + or - charge depending on pH
- strong adsorption of P
- Amourphous
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
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
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
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
14
Q
Clay collids
A
morphous structure
15
Q
Humus collids
A
- intermediate product of highly decomposed orgo mat
- amorphous structure
- most stable form of orgo mat in soils
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
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
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
what is Laterization?
- 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
How does laterization occur?
- removal of vegitation
- increases ersosion
- repeat wetting and drying
- Fe, AL Si leached into lower columb forming a brick like
27
characterisitics of Laterite soils
- 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
low rainfall and humidity
| l
low rates of decomposition, slowing soil formation
29
parent matieral high in quartz
difficult to break down into secondary, slowing soil formation
30
High clay content
Aeration and water movment are poor, slowing soil formation
31
steep slopes
high erosion and constant exposure of bedrock, sows soil formation
32
High water table
33
Continued deposition of new matieral
no chanve for horizon developement, solwing down soil formation
34
O,A,B,C
- Organic horizon
- A mineral horizon, (roots)
- B Transitional Zone
- C unconsolidated rock
35
Oxisols and Ultisols
(ferralsol)
- deep,reddish, acidic, highly weathered
- high Fe Al oxides, low fert, low OM
- 36% of topics
- humid and subtropics along with some savannas
36
Alfisol(luvisol)
- 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
Entisols (regosol)
- 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
38
Inceptisol (cambisol)
- young soils
- ditincct horizon
- very fertile
- dev on land covered by volcanic rock
- occupy 12% of tropical lands
39
Terra Preta do Indo
- 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
undistured soils in the tropics
are productive
- loss little nutirents due to plant cover, no leaching
- nutirent accumulation through rainfall, lighting, dust , nitrogen fixers, root nutient pumps
41
Conversion of virgin tropical rainforest to agricultural land
- 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
