mid-latitude grasslands part two
DESCRIPTION
Mid-latitude Grasslands Part Two. Soils Chernozems/Mollisols. 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 - PowerPoint PPT PresentationTRANSCRIPT
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