1. Mid-latitude Grasslands Part Two
Soils
Chernozems/Mollisols

2. Chernozems or Black Earths
Optimum soil for agriculture
Deep & rich
Retains moisture
Crumb structure with well formed peds (groupings of soil particles)
Lots of mull humus gives a black, crumbly topsoil
(Mull humus is mixed throughout depth of soil, mor humus forms a distinct layer at the top due to poor decomposition e.g. cold wet uplands.

3. Soil Profile Abundance of biota (esp. earthworms)
Rapid decay & mixing in summer
Humus spread throughout ‘A’ horizon up to 1m
Decomposition arrested in drier spells & long, cold winter

4. Movement of water & bases
Slight Leaching
Bases (potassium & magnesium) slowly moved down through soil profile
Caused by late spring snowmelt & early summer storms
Capillary Action
Water and dissolved bases drawn upwards due to evaporations from the surface in late summer
Helps maintain pH 7-7.5

5. Why no ‘B’ horizon? Alternating wet & dry seasons
Immobilises iron & aluminium sesquioxides & clay within aggregates (peds – soil clusters)
Large number of mixing agents e.g. earthworms
Limits formation of recognisable ‘B’ horizon

6. Subsoil Often loess origin (wind deposited) Usually porous
Capillary action occurs in summer
Usually porous
(allows water movement)
Calcium carbonate
nodules deposited in
‘C’ horizon as a result of
Capillary action.
Calcification is the term
for the accumulation of
calcium.
Therefore
subsoil is dry
After intense ploughing may require addition of potassium & nitrates.

7. Water Balance Ppt > Evapotranspiration Ppt = Evapotranspiration
Prairie Soils
Chernozems
Chestnut Soils
No capillary action
Less calcium
carbonate
Less vegetation as it is
drier
-Less organic matter in
soil
-Smaller, lighter ‘A’
horizon

8. Efficient Recycling of Nutrients

9. Destruction of Prairies
West
<23% true short
grass prairie left
Centre
<34% true
mixed grass
prairie left
East
Little tall grass
prairie left

10. For Human Impact
See P.P.6