Related to Inceptisols
Acidic, humid tropics
Oxic (Bo) horizon
Residual Fe and Al
Not found in continental US
Agrillic (Bt) horizon
Base saturation over 35%
Typical forest soil of midwest
Grassland soils (farm-belt)
High in OM
Fertile, bas saturation above 50%
Mollic horizon, typically cultivated
more develope than entisols but still young
Finer textured than Entisols with a cambic horizon
Dead organic material undergoing decomposition.
Oi and Oe horizons.
|Principles governing exchange reactions||
|Lime as an acid neutralizer||
|Sources of H+||
1.carbonic acid-from rain
3.organic matter-produces H when it decays
4.uptake-plants often release H+ to balance their charge when they uptake cations.
5.Aluminum (especially below pH of 6)-dissacociates from the clay minerals.
detritovores. enhance nutrient cycling. bring surface nutrients downwards.
Macro detritivore. engineer burrows which naturally till soil. Casts enhance nutrient cycling.
Water-stable protein excreted by a guild of rhizosphere fungi. Coats soils particles, acting as glue to bind aggregates.
Weight (solids only)/volume (solids and pores)
1.33 is an ideal soil bulk density. Above 1.6 starts to make root growth difficult.
Compaction increases bulk density, influences movement of water and gases.
|Factors mediating CEC||
1.exchanges are reversible
2.exchanges are charge-for-charge
3.ions in equilibrium with solution (most important)
5.exchange sites are cation selective
OM increases buffering
finer textured soils are better buffered
Physical and chemical alteration of materials from which soils form. Process for soil formation.
|Benefits of Lime||
Increases base cations/base saturation
Increases nutrient availability
Improves soil structure
Promotes microbial growth
Minimizes acidifying effects of fertilizers
Reduces metal toxicity to plants
|CEC by % clay and O.M.||
1. Organizes knowledge about soils
2.Groups soils with similar properties
3.Provides meaningful basis for soil mapping and management
Diagnostic horizons are key to soil taxonomy
A horizon; Northwest USA
Like mollic but lower in carbonates
Forest soils with thick A horizon
Found on young, coarse textured soils
Weakly developed, always above C horizon
herbivores. shredders- reduce size of plant matter.
Arrangement of soil particles. Grouped spatially into aggregates
Aggregates form through physical-chemical processes and biological activity
Aggregates change soil properties
Influences water movement, fertility, pore space, and biodiversity
A horizon; Easter US forest soils
Pale color, lower OM
Low base saturation
Thinner A than mollic and umbric
Hard and massive structure when dried
Protects soil from changes in temperature, moisture, and disturbance. Creates cooler, moister, and higher fertility soils.
silicon surrounded by four oxygens. One of two fundamental units of silicate clays.
|Soil Pore Space||
Function of texture and structure. Macropores a function of structure and micropores a function of texture. Small pores generally good for water and nutrient movement. Larger pores good for gas exchange and root growth.
Al(OH)^2+ + H2O <--> Al(OH)2^+ + H+
Al(OH)n^+ + H2O <--> Al(OH)3 + H^+
Method of acid buffering
feed on fungi, bacteria, algae ro are predatory. Release nitrogen from eaten bacteria and control insect pop.s . some parasitic to plants
|Five factors of soil formation||
Climate (water and heat)
Organisms (add organic matter, organic acids)
|2:1 silicate clay||
when each clay layer has one octahedral sheet sandwiched between two tetrahedral sheets.
Smectite and vermiculite (expanding/ Due to water filling in micropores)
illite (mica) and chlorite (nonexpanding)
|Iron and Aluminum Oxides||
Iron or Aluminum hold cation position in octahedral sheet. Isopmorphous substitution is rare, not much charge.
|Soil Formation Processes||
Translocation (Illuviation and Elluviation)
Addition (organic matter or deposition)
Losses (Leaching or erosion)
Argillic horizon with <25% base saturation
Southeastern US forest soils (acid rain may be turning Alfisols of SE Ohio into Ultisols)
Crack and open when dry (plowing itself)
|Unit of Charge||
Interface between lithosphere, atmosphere, biosphere, and hydrosphere where soil lies.
No pedogenic horizons
Alluvial beech sand; coarse texture
Bo horizon; tropical regions
Highly weathered soils, low cation-exchange
Accumulation of Fe and Al
Poor for agriculture
Minerals: products of weathered minerals
High water holding capacity
Available water low
|What is Soil?||
A matrix of....
dead organic matter
single celled predators. control bacteria populations.
herbivores and detritovores. less beneficial to soil productivity. bring subsoil upwards.
Total base cations/CEC
Basis for knowing soil fertility. 50% and below is generally bad.
Bt horizon; common throughout SE Ohio
High percent of clay
Required long time to form (geomorphic stability)
Typical of forests (undisturbed)
Central Aluminum or magnesium surrounded by 6 oxygens. One of two fundamental units of silicate clays.
|Total soil water potential||
gravitational potential+matric potential+hydrostatic potential+osmotic potential
CaCO3 + H2CO3 <-->Ca(HCO3)2
Ca(HCO3)2 + H2) <--> Ca^2+ +2OH^- +H2CO3
Mechanism of base buffering
|Five Master Soil Horizons||
E-zone of elluviation
B-zone of accumulation
C-zone of least weathered parent material
Material displaced across a soil profile by water
Muck and peat
Saturated with water
Thick (> 20 cm)
Very high OM (>12%)
Elluvial horizon below A horizon
Light in color, no coating of Fe (all leached away leaving just sand and quartz)
Also forms over long periods of time
If a Bt horizon is present, an E horizon must also be present. (indicative of old-growth)
"A zone of accumulation necessitates a zone of leaching"
Arid and dry
High base saturation
Salt accumulation at depth (Caliche layer like concrete)
Reduction in particle size
Freezing and thawing (frost wedging)
Heating and cooling
Water and wind (most prevalent, especially for sedimentary rocks)
minerals: quarts or other primary silicates such as feldspar
Low water holding capacity
Available water very high
Fine-loamy, mixed, active, mesic Typic Hapludalf
The stacking of clay platelets with cations such as calcium and sodium. Adding lime will improve soil structure, makes it more granular.
Minerals are decomposed by chemical reactions. Primary minerals into decondary minerals.
Hydration (binding of water to mineral ion; rust)
Hydrolysis (mineral breakdown by water)
Redox (oxidation and reduction)
Complexation (decomposition by organic acids)
Dissolution (water dissolving minerals)
Supports life. Primary mechanism in nutrient transport to plant roots.
Acid leaching soild; Northern US and Florida
Spodic horizon (Bs)
Has an E horizon
Acidic, sandy soils
Acidic, coarse textured forest soil
A or B horizon
Illuvial horizon formed under cultivation (plowing)
Directly below an Ap horizon
Creates unique floral and faunal community
|Hydrated ion radius||
electrostatic attraction of water to an ion. Depends on ions density and charge. Greater water attraction for smaller ions. Larger radii indicate weaker attractions.
|Soil Organic Matter||
Generall 5% is important. Improves soil fertility, improves water-holding capacity, and buffers soils against change.
Al^3+ + 3H20 ---> Al(OH)3 + 3H^+
Volume of soil solids to volume of soil. Ideal soil is 50% solids and 50% pore space.
|Cation exchange capacity||
sum total of the exchangeable cations that a soil can absorb. Expressed as the number of moles of positive charge adsorbed per unit mass.