UBC Farm Soil Workshop Series

1. UBC Farm Soil Workshop Series Class 1: Introduction to Soil Formation, Texture and Structure Chris Thoreau February 11, 2012

2. What is Soil? • Soil is a dynamic composition of: • Minerals • Water and its solutions • Organic matter (detritus) • Air and other gas mixtures... • ...which, through interacting with each other and with plant roots, allows for the growth of photosynthesizing terrestrial plants • …and acts as a habitat for micro- and macro-organisms • …which also interact with plants and plant roots • Or…

3. What is Soil? • Physical Aspects: • Minerals (from rocks) • Sand • Silt • Clay and Colloids • Organic Matter • Plants and Roots • Detritus (decaying organic matter) • Animal waste (including microbes) • Pore Space • Air/Gases • Water

4. What is Soil? Soil is the Mother of All Terrestrial Life

5. What is Soil? • Conceptual Aspects: • Habitat • Micro-organisms • Bacteria, Fungi – both good and bad • Viruses • Macro-organisms • Worms, Arthropods, Detrivores and Predators • Plants • Small Mammals • Birds

6. What is Soil? • Conceptual Aspects: • Provider to plant life • Rooting substrate • Water holding and release • Nutrient supply and reserve • Heat sink and release • Soil gases • Symbionts • Bacterial and fungal • Insects

7. What is Soil? • Habitat • What happens when we disturb this habitat? • At micro and macro level? • What happens when we make additions to, or removals from, this habitat? • Carbon:Nitrogen ratio? • How do soil organisms and plants respond? • Nutrient loss or gain? • Providing for plant life • What are the short-term and long-term results? • Are we providing for the soil as well as the plants? • What is the difference?

8. What is Soil? • As a habitat we need to treat soil like a living organism, which requires: • Food • Organic Matter and Minerals • Water • Irrigation and Natural • Air • Shelter • Cover crops, Cash Crops, Mulches • General tender loving care…

9. What is Soil? Questions?

10. Soil Formation Where does soil come from? Soil comes (mostly) from the weathering of rocks over long periods of time – a process highly influenced by biological organisms, topography, aspect and human activity…

11. 5 Factors of Soil Formation 1. Parent Material 2. Climate 3. Biota 4. Topography 5. Time

12. 5 Factors of Soil Formation 1. Parent Material • Transported • Gravity - Colluvial • Water – Alluvial, Marine, and Lacustrine • Wind – Eolian • Ice – Glacial • Cumulose • Due to plant life and anaerobic conditions • High water table • Peat and muck soils • Residual • In situ; long periods of weathering

13. 5 Factors of Soil Formation 2. Climate • Temperature and rainfall are major factors • Affect intensity of weathering • Increased T and precipitation accelerate weathering 3. Biota • Plants influence organic matter • Arthropods and worms mix soil; add to OM • Small mammals also mix soil

14. 5 Factors of Soil Formation 4. Topography • Slope influences soil development • Water infiltration rate • Surface runoff • Vegetation • Aspect • North and South slopes develop differently • Elevation • Climate changes with altitude

15. 5 Factors of Soil Formation 5. Time • Often noted as most important soil formation factor • Our soils in Lower Mainland are relatively young • Since last ice age 10-12,000 years ago

16. Weathering of Rocks • Primary Minerals  Sand and Silt • Formed at high T and P (at depth); anaerobic conditions • Physically and chemically formed • Quartz, Feldspars, Micas, • Secondary Minerals  Clay • Come from primary minerals • Formed at low T and P (at surface) with Oxygen present • Mostly chemically formed • Silicate Clays

17. Weathering of Rocks Weathering of Rocks Physical Chemical 1 Chemical 2

18. Soil Formation Processes Additions Losses Transformations Translocations

19. Soil Horizons

20. Soil Horizons • Organic (O) Horizon • High in organic residue from plant drop • A Horizon • Mineral component plus OM • Most fertile part of soil; location of much root activity • B Horizon • Subsoil • A horizon leaches here • C Horizon • Little influence by soil-forming processes

21. Soil Orders of Canada In a given area, over the period of soil formation, environmental conditions cause a certain set of soil processes to occur, which leads to a distinctive set of soil horizons at the time we observe the soil.  These soil horizons are the basis for classifying the soil in the Canadian System of Soil Classification. 

22. Soil Orders of Canada

23. Podzol Gleysol Chernozem Brunisol Luvisol Organic Solonetzic Vertisol Regosol Cryosol Soil Orders of Canada

24. Podzol Soil Video here

25. Soil Formation • Any questions? • Check follow up readings and websites for more detailed information • UBC Virtual Soil Science • Soil Orders of Canada Videos • Canadian System of Soil Classification

26. Soil Texture Soil texture refers to the relative amount of sand, silt, and clay found in a soil The mixture of these components affects the feel of the soil as well as water, nutrient, and pore space interactions

27. Soil Texture • Mineral Components • Sand • Silt • Clay

28. Soil Texture Mineral ratios determine soil texture

29. Soil Texture • Sand • Largest soil mineral particles (.02 – 2 mm) • Formed greatly from physical processes • Spherical/erratic in shape • Sand = little rocks • Larger pore spaces • Good drainage • Does not hold a charge • Difficult to compact

30. Soil Texture • Silt • Size between sand and clay (.002 - .02 mm) • Usually physically formed out of sand • Hold and releases water well • Flat or round in shape • Holds very little charge • Feels soapy • Carried in moving water

31. Soil Texture • Clay • Smallest soil mineral particle (< .002 mm) • Holds water very well • Holds strong negative charge for mineral adsorption • Susceptible to compaction • Platy-/flat-shaped particles • Various lattice structures

32. Soil Texture • Clay • Understanding structure of clay is important for: • Compaction • Water holding • Cation adsorption • Soil cultivation • Clays are categorized by their layer structure • Relationship of Si-tetrahedral and Al-octahedral sheets • 2:1; 1:1; 4:1; 5:2

33. Soil Texture 2:1 Clay • Shrink and swell 1:1 Clay No change

34. Soil Texture • Shrink and Swell of Clay • Interlayer space expandswith increasing watercontent in soil • Space contracts as wateris removed • Clay can crack when it shrinks

35. Soil Texture • Why is Texture Important? • Water Infiltration • Water Storage • Fertility • Aeration • Trafficability • Soil texture knowledge is the key to developing an overall soil maintenance and improvement plan

36. Soil Texture • Notes: • We do not change the texture of soils • We can change the characteristics of certain textured soils • We change soil characteristics through: • Additions of organic matter • In soil and on top of soil • Cultivation practices • Raised beds

37. Soil Texture Attributes of Different Soil Textures

38. Soil Texture • We can determine the texture of the soil by feeling it • Ribbon test • Ball test • Jar test • Laboratory tests give more accurate results

39. Soil Texture • Texture Questions?

40. Soil Structure • Soil Structure: How the soil fits together • Primary particles are arranged into secondary particles called aggregates (or peds)

41. Soil Structure • Why is Structure Important? • Pore space • Air and water movement • Rooting space • Nutrient storage and release • Contributes to soil resilience • Cultivation • Erosion resistance

42. Soil Structure • How does aggregate formation occur? Flocculation + Cementation = Aggregation • Flocculation: • Primary pulled close together (into flocs) by attractive forces (electrostatic forces, H bonding) • Cementation • Primary particles held together by cementing agents • Carbonates; clays; OM; Oxides

43. Soil Structure

44. Soil Structure • Soil Aggregates are classified by their shape

45. Soil Structure • Ideal structure: Spheroidal • Typical in A Horizon • Rounded; loose • Granular (porous) or Crumb (very porous) • Greatly affected by soil management OR mismanagement • Improved with OM additions and microbial activity

46. Soil Structure • Soil structure is particularly important in providing adequate pore space for: • Root growth • Water movement • Gas exchange • Microbial activity • Macrobial activity

47. Soil Structure Structure can be easily observed in the soiland structural stability, or aggregate stability, can be measured in the lab Structure can be improved, to a point, by soil cultivation. Soil cultivation is also a great way to destroy structure

48. Soil Consistency • Related to texture • Very important when considering soil cultivation • Dependent on: • Texture/clay content • Clay type • Soil water content

49. Soil Consistency

50. Soil Consistency • Cultivating soil when too dry • Breaks aggregates into small pieces • De-aggregates • Can result in dust • Very damaging to soil structure • The drier the soil – the more it acts like powder