Soils 205-90

Lecture 23 The Soil Orders

Videos                                                       Pages in text

*note:  when going through this material please make use of the following website:

http://soils.ag.uidaho.edu/soilorders/

Soil Orders

1. Entisols

(a) few, in any, genetic horizons

(b) highly variable properties

sands ¬¾¾® alluvium

(c) lack development

(d) productivity - variable

(e) location - any climate

2. Inceptisols

(a) inceptum (L.), beginning

(b) quickly formed horizons like cambic

w more developed than entisols

less than others

w no clay movement or eluviation

(c) productivity - variable

(d) location - any location or climate

w numerous in N. Idaho

3. Aridisols

(a) aridus (L.) - dry

(b) horizons dry for major part of year

unless, ground water or irrigation

w not extensively leached

w often contain lime, gypsum and/or salt in upper profile

- calcic, gypsic or duripans

(c) ochric epipedon

(d) may have argillic or natric

(e) common in S. Idaho - Snake River plain

(f) if irrigated - often productive

- very important in Western U. S.

4. Mollisols

(a) mollis (L.) - soft

(b) mollic epipedon results in a mollisol

(c) structure - granular (soft)

(d) may have argillic, albic, natric, cambic

- not spodic nor oxic

(e) high bases and O.M. - productive, rich

(f) usually, prairie (grassland) vegetation

some, forest

(g) variable leaching

- some are calcic

 

(h) some of the worlds most productive soils

w great plains, palouse, Ukraine, Russia, China

5. Alfisols

(a) gray to brown surface - ochric

(b) have an argillic with medium to high base saturation (BSP)

w 2:1 layer lattice clays

(c) no mollic, oxic nor spodic

(d) more weathered than Inceptisols (have an argillic)

less weathered than Spodosols (no spodic) or Ultisols (more bases)

(e) humid regions - deciduous forest and grass

some conifer (Idaho)

(f) quite productive soils

w medium to high bases

w but, some fragipans - restricts depth

6. Spodosols

(a) Spodos (Gr.) - wood ash

(b) cool to cold and humid climate

(c) coniferous forest vegetation

(d) Genesis:

w slow decomposition of litter layer + acidic conditions

w leaching through organic matter layer

w solubilize Fe and Al (acid + soluble organics)

w eluviated SiO layer (Fe and Al eluviated)

w illuviated spodic horizon (Fe, Al, O.M.)

(e) must have spodic horizon

(f) often have albic horizon (Si oxide)

light color = "wood ash"

(g) highly leached and acid soils

(h) limited productivity - acid, low CEC, highly leached

(i) old term - true Podzols

7. Ultisols

(a) Ultimus (L.) - last

(b) warm to tropical climates

(c) older land forms

(d) have argillic or kandic with low base saturation (BSP)

w low activity clays (1:1 and hydrous oxides)

(e) more weathered than alfisols (lower base saturation)

less weathered than spodosols (no spodic) or oxisols (no oxic)

(f) color is commonly red-yellow

w from Fe oxide release

(g) have some weatherable minerals - kaolinite

(h) commonly, warm forest vegetation

(i) Southeast U. S.

(j) low native fertility (leached)

w but long growing season + non-swelling clays + high moisture

- respond to good management (lime)

8. Oxisols

(a) have oxic horizons

w deep accumulation of clay-sized oxides of Fe and Al

(b) intense weathering - hot, humid climate

(c) "tropical" soil

w warm temp - rapid O.M. decomposition

w removes Si

w leaves Fe and Al oxides - intense red color

+ some quartz and 1:1 silicates

(d) very high clay content

w non-swelling - easily worked & highly structured

(e) termed Latosols or Laterites (very old surfaces)

(f) large areas and population in the tropics

(g) high rainfall = leaching of bases

= acid problems

(h) high P fixation

(i) low CEC and high pH-dependant charge (+ and -)

(j) very highly weathered = brick or rock

9. Vertisols

(a) high content (> 30 %) swelling-type clays

(b) verto (L.) - to turn (self-mixing)

(c) large shrink-swell = cracks

(d) old term - Grumusols

(e) very unstable - difficult to work

(f) wet - stickey and plastic

dry - hard

(g) very "heavy" soils

(h) depositional - little horizonation

(i) productivity - very difficult to manage

(j) engineering properties - poor infiltration, unstable

10. Histosols

(a) histos (Gr.) - tissue

(b) organic soils

(c) excessive water (saturation) = slow organic residue decomposition

(d) any climate

(e) if low clay - > 12 % C is required

if high clay - > 18 % C is required

(f) low D_b and high water-holding capacity (on weight basis)

(g) can be very productive

w subside, if drained

w mined

11. Andisols

(a) developed in volcanic ash & pumice

(b) ando (dark soil) - can have melanic epipedon

(c) not highly weathered

w no illuviation

(d) amorphous Si minerals (allophane, imogolite)

(e) previously, inceptisols

(f) can be productive

w high available-water-holding capacity

w easily worked (low D_b)

w problems

- P fixation

- erosive

(g) large areas from Mazama ash in N. Idaho

12. Gelisols

(a) permafrost layer

w below 0^oC for more than 2 years

(b) often have frost turning

w patterned ground

(c) little profile development

w cold, frozen conditions

(d) active layer above permafrost

w some diagnostic horizons

(e) large areas in northern climates (Alaska)

w important wildlife areas

(f) construction limitations

w wet, with poor bearing strength

w if disturbed - melt & unstable

(Alaska pipeline on stilts)

(g) low plant productivity

w poor drainage

w short growing season

 

13. Climate and Soil Orders