Presentation on theme: "Mid-latitude Grasslands Part Two"— Presentation transcript:
1 Mid-latitude Grasslands Part Two SoilsChernozems/Mollisols
2 Chernozems or Black Earths Optimum soil for agricultureDeep & richRetains moistureCrumb 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 summerHumus spread throughout ‘A’ horizon up to 1mDecomposition arrested in drier spells & long, cold winter
4 Movement of water & bases Slight LeachingBases (potassium & magnesium) slowly moved down through soil profileCaused by late spring snowmelt & early summer stormsCapillary ActionWater and dissolved bases drawn upwards due to evaporations from the surface in late summerHelps 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. earthwormsLimits formation of recognisable ‘B’ horizon
6 Subsoil Often loess origin (wind deposited) Usually porous Capillary action occurs in summerUsually porous(allows water movement)Calcium carbonatenodules deposited in‘C’ horizon as a result ofCapillary action.Calcification is the termfor the accumulation ofcalcium.Thereforesubsoil is dryAfter intense ploughing may require addition of potassium & nitrates.
7 Water Balance Ppt > Evapotranspiration Ppt = Evapotranspiration Prairie SoilsChernozemsChestnut SoilsNo capillary actionLess calciumcarbonateLess vegetation as it isdrier-Less organic matter insoil-Smaller, lighter ‘A’horizon