Presentation on theme: "Mid-latitude Grasslands Part Two"— Presentation transcript:
1Mid-latitude Grasslands Part Two SoilsChernozems/Mollisols
2Chernozems 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.
3Soil 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
4Movement 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
5Why 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
6Subsoil 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.