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Mid-latitude Grasslands Part Two

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Presentation on theme: "Mid-latitude Grasslands Part Two"— Presentation transcript:

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

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