GY1004 Principles of Physical Geography B Lectures 5-6 Soils

1. GY1004 Principles of Physical Geography B Lectures 5-6 Soils DEPARTMENT OF GEOGRAPHY

2. Soil processes and patterns The soil process-response system Horizonation processes Soil types, classification and the global distribution of soils

3. Soil process-response system

4. Horizonation processes Lessivation Leaching Translocation Mixing

6. Clay cutans Lessivation The finer the texture of the soil, the greater is the effective surface area exposed by its particles

8. Rainwater Leaching Leaf litter L A Eb Bt C Organic acids H+ Leaching and loss of clay particles, acc. of organic matter Clay particles Ca2+ Mg2+ Na+ K+ Accumulation of clay, iron and bases Some loss (Ca2+ Mg2+ Na+ K+) Some loss to drainage water

9. Re-precipitation of CaCO3

10. A Bk C Rainwater Mollisol Leaf litter Organic acids H+ Very slight leaching, accumulation of organic matter Ah Bw Slight gain (Ca2+ Mg2+ Na+ K+) Slight loss (Ca2+ Mg2+ Na+ K+) Bk Virtually no loss to drainage water Calcification

11. Rainwater Leaf litter Organic acids H+ colloidal organic matter O Eag Bh Bf Leaching and breakdown of clay materials Colloidal organic matter Fe, Al, Si, N, Ca2+ Mg2+ Na+ K+ Accumulation of colloidal organic matter, Iron and aluminium Serious loss of N, Ca2+ Mg2+ Na+ K+ Loss to drainage water Humus iron pan podsol Podsolisation O A Ea B C

12. Pedalfers and Pedocals PedALFErs Aluminium (Al) and iron (Fe) rich PedoCAls Calcium (Ca) rich

13. Very little rainfall Re-evaporation Salt crust A B C Stable structure with neutral salts Gains of N+ Mg2+ Cl- SO-4 Transmission of salt by capillarity deposition of salts in pores and fissures Gains of Na+ Mg2+ Cl- SO-4 Upward translocationSalinisation

14. Gleying

15. Bivalent (Fe2+) Ferrous iron oxide FeO (Reduced form) Trivalent (Fe3+) Ferric iron oxide Fe2O3 (Oxidised form) Laterite Gley soil

16. Soil process-response system

17. Factors controlling soil development Climate Parent material Vegetation/organic matter Topography/relief Time

18. The influence of climate

19. Variation in the character of the weathered mantle in relation to climate (Strakov, 1967)

20. The influence of topography

21. Catena

22. Zonal soil classification

23. Zonal soil classification Zonal Azonal Intra zonal

24. Comprehensive Soil Classification System CSCS Mollisols Aridisols aridus; solum Inceptisols inceptum; solum Order 12 Suborder 63 Great group 250 Sub group 1,400 Family 8,000 Series 19,000 (USA only)

25. Entisols Inceptisols Andisols Gelisols Histosols Oxisols Ultisols Vertisols Alfisols Spodsols Mollisols Aridisols The twelve soil orders of the CSCS

26. Inceptisol Gelisol Andisol Entisol

27. Vertisol Oxisol Histosol Ultisol

28. Alfisol Spodsol Mollisol Aridisol

30. Summary The internal characteristics of a soil depend on the operation of horizonation processes (leaching, gleying, translocation). Fundamental differences in soils are found over the Earth’s surface as a result of differences in soil forming processes.

31. Summary The intensity of these processes is controlled by five major factors: climate, parent, material, vegetation, relief and time. These processes operate at a range of scales and control both the global and local distribution of soil types.

32. Summary It is possible to define environmental domains for different soils and develop zonal models of soil development and classification on the basis of formative processes. The US Comprehensive Soil Classification System, however, classifies soils on the basis of their physical characteristics, rather than formative processes. It is a six-level hierarchical classification based on 12 broad soil orders.