Presentation on theme: "Mid-latitude Grasslands Part Two Soils Chernozems/Mollisols."— Presentation transcript:
Mid-latitude Grasslands Part 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
Subsoil Often 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 of Capillary action. Calcification is the term for the accumulation of calcium. After intense ploughing may require addition of potassium & nitrates.
Water Balance Ppt > EvapotranspirationPpt = EvapotranspirationEvapotranspiration > Ppt Prairie SoilsChernozemsChestnut 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
Destruction of Prairies West <23% true short grass prairie left Centre <34% true mixed grass prairie left East Little tall grass prairie left