Mid-latitude Grasslands Part Two

1. Mid-latitude GrasslandsPart Two Soils Chernozems/Mollisols

2. 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. Chernozems or Black Earths

3. 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 Soil Profile

4. 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 Movement of water & bases

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) 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 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

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