Mid-latitude GrasslandsPart Two

Soils

Chernozems/Mollisols

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.

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

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

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

SubsoilOften loess origin (wind deposited)

Usually porous(allows water movement)

Capillary action occurs in summer

Therefore subsoil is dry

Calcium carbonate nodules deposited in

‘C’ horizon as a result ofCapillary action.

Calcification is the termfor the accumulation of

calcium. After intense ploughing may require addition of potassium & nitrates.

Water Balance

Ppt > Evapotranspiration Ppt = Evapotranspiration Evapotranspiration > Ppt

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

Efficient Recycling of Nutrients

b) Steppe & Prairie (mid-latitude continental grassland)

biomass

litter

soil

Little runoff asLittle ppt.

Highdecompositiondue to wet & dry seasons &

bacteria

Low ppt meansless loss of nutrients

from leaching

Weather encourageschemical & physical weathering releasing

nutrients to soil

Large store of nutrients due togood drainage

Small store due to climate, insufficient moisture to support

trees & growing season reduced to 6 months

by cold temps. Much ofbiomass beneath surface

as rhizomes & roots

High supply of

litter, grassesdie back in

winter

Littleppt.

Litter store small as no trees, grasses

die back quickly into soil Some plants store their

own nutrients inrhizomes & roots so not as many nutrients taken

up from soil

Destruction of Prairies

West

<23% true short grass prairie left

Centre

<34% true mixed grassprairie left

East

Little tall grassprairie left

For Human Impact

• See P.P.6