What is soil?

1. What is soil?

2. Merriam-Webster Online Dictionary • Main Entry: 3soil, noun1: firm land : EARTH2 a: the upper layer of earth that may be dug or plowed and in which plants grow b: the superficial unconsolidated and usually weathered part of the mantle of a planet and especially of the earth3: COUNTRY, LAND <our native soil>4: the agricultural life or calling5: a medium in which something takes hold and develops

3. Definitions, Byers, et al., Formation of Soil, 1938* • Soils are natural media for the growth of plants. They are mixtures of fragmented and partly or wholly weathered rocks and minerals, organic matter, water, and air, in greatly varying proportions, and have more or less distinct layers or horizons developed under the influence of climate and living organisms…Soils are dynamic in character …the product of the action of climate and living organisms upon the parent material, as conditioned by the local relief. • *Yearbook of Agriculture

4. Definition, Soil Science Glossary, SSSA, cont’d • (ii) The unconsolidated mineral or organic matter on the surface of the earth that has been subjected to and shows effects of genetic and environmental factors of: climate (including water and temperature effects), and macro- and microorganisms, conditioned by relief, acting on parent material over a period of time. A product-soil differs from the material from which it is derived in many physical, chemical, biological, and morphological properties and characteristics.

5. Definition, Soil Taxonomy, 2nd ed. • The lower boundary that separates soil from the nonsoil underneath is most difficult to define. Soil consists of horizons near the earth's surface that, in contrast to the underlying parent material, have been altered by the interactions of climate, relief, and living organisms over time. Commonly, soil grades at its lower boundary to hard rock or to earthy materials virtually devoid of animals, roots, or other marks of biological activity. For purposes of classification, the lower boundary of soil is arbitrarily set at 200 cm.

6. Soil Classification sand; 2 - 0.5mm silt; 0.002 - 0.5mm clay; <0.002mm Soil Texture = proportion of sand,silt,clay Soil Texture -> water retention organic matter stabilization

7. O-Horizon • Soil horizons are the layers in the soil. The top layer is the O horizon. The O horizon is the organic material. It’s only about an inch thick, but it is very healthy. However, it may not always be present.

8. Soil Development Soil horizons are distinct layers in the soil with particular properties 4processes contribute to horizon formation: transformations: soil components are modified, destroyed, synthesized 2. translocations: movement of materials 3. additions: materials added to soil from outside 4. losses: materials are removed from soil

9. Soil Master Horizons O -- organic material A-- contains organic material. Minerals are leached from here and moved downward (eluviation) B -- contains little organic material. Minerals and clay from above are deposited here (illuviation) C --unconsolidated rock

10. Soil Master Horizons E -- leached horizon where secondary minerals and organic matter are removed Master Horizon Modifiers Bt= accumulation of silicate clays Bo=accumulation of Fe,Al oxides Ba=accumulation of organic matter

11. Soil Classification: USDA Soil Taxonomy Soils are classified based on morphological properties: surface horizons, subsurface horizons Presence/absence of particular soil horizons is important for classification Climate regime

12. Classification Structure Orders 12 Suborders 63 Great Groups 250 Sub Groups 1400 Families 8000 Series 19000 (in US) Aridic Ustipsamment Typic Durixeralf Typic Duri-xer-alf sub group, great group, sub-order, order (modifiers: texture, mineralogy, climate)

13. Soil Orders Alfisols -- high to med. base saturation. Older landscapes but not extensively leached. Not as weathered as Ultisols Andisols --volcanic parent material. Non crystalline clays, high organic matter Aridisols -- Arid environment. Light colored A horizon. Some B horizon development. Entisols -- young soil, lacking horizon development Gelisols -- showing freeze/thaw mixing Histosols -- large organic horizon

14. Soil Orders Inceptisols -- young, weakly weathered. Few diagnostic horizons Mollisols --well developed horizons, high in organic matter and calcium. High base saturation. Oxisols --highly weathered soil, Fe, Al oxides. Low CEC Spodosols --leached E horizon. B horizon with organics, Al, Fe oxides Ultisols --Low base saturation. Weathered soils, but not as much as Oxisols Vertisols --high shrink/swell clay content. Cracks

15. State Soil of Florida: Myakka Series Sandy, siliceous, hyperthermic Aeric Alaquods Surface layer: gray fine sand Subsurface layer: light gray fine sand Subsoil: dark reddish brown fine sand with organic stains Substratum: brown and yellowish brown fine sand http://soils.usda.gov http://www.fao.org

16. Dark Gray Luvisol Orthic Humo-Ferric Podzol Orthic Black Chernozem Soil have distinct properties

17. US Spodosol Distribution

20. Soil Reaction • Soil reaction is the degree of acidity or alkalinity of a soil, usually expressed as a pH value. • Soil pH = -log [H+] • Soil pH is an indicator of physical, chemical and biological properties in soil. • Soil pH is also related to the cations present on the exchange complex.

21. Descriptive terms for Soil pH ranges

22. 16 r Particle size & pore space Large Particle 2 x 2 x 2 = 8 Pore radius = 4r

23. 16 r Particle size & pore space Medium Particle 4 x 4 x 4 = 64 Pore radius = 2r

24. 16 r Particle size & pore space Small Particle Pore 8 x 8 x 8 = 512 radius = r

25. Pores and particles in soil (Pawluk)

26. Finding and Describing Horizons Soil Pit Technique Starting from top, observe profile to determine properties and differences between horizons. Place golf tee or marker at the top and bottom of each horizon to clearly identify it. Look for: different colors, shapes, roots, the size and amount of stones, small dark nodules (called concretions), worms, or other small animals and insects, worm channels, and anything else that is noticeable. Soil formed under very dry or arid conditions in New Mexico, USA

27. Finding and Describing Horizons Exposed Profile (Road Cut) Technique Obtain permission to take samples from the road cut, excavation, or other soil profile exposed by others. Obey any and all safety precautions requested. Expose a fresh soil face by scraping approximately 2cm off of the vertical surface of the soil profile. Follow Soil Pit Technique directions.

28. Finding and Describing Horizons Auger Technique 1. Identify an area where you can dig four holes where the soil profiles should be similar. 2. Spread a plastic bag, tarp, board, or other surface on the ground next to where you will dig your first hole. 3. Assemble a profile of the top 1 meter of the soil by removing successive samples with the auger and laying them end-to-end as follows: 4. Identify each horizon and measure its thickness using the depth of the auger hole.

29. Finding and Describing Horizons Surface Sample Technique In situations where it is not possible to expose the top meter of soil, another option is to use the top 10 cm of soil as a horizon sample for soil characterization. 1. Use a garden trowel or shovel to carefully remove the top 10 cm of soil from a small area and set it on the ground. 2. Treat this sample as a horizon and proceed to characterize its properties.

30. Soil Has Texture The way a soil feels when you touch it is called its “texture”.

31. Horizon Properties Soil Structure Soil structure is the shape that the soil takes based on its physical and chemical properties. Each individual unit of soil structure is called a ped. Possible choices of soil structure are: With Structure: Blocky Granular Actual size Actual size Columnar Platy Prismatic Actual size Single Grained Massive Structureless: See hands for relative size Pencil is 19 cm

32. Gritty A soil that feels “gritty” is made up of sand, the largest pieces of soil.

33. Soft Soil A soil that feels soft, silky, or “floury” is made of the medium size soil pieces called silt.

34. Sticky Soil The smallest size soil pieces are clay. Clay feels “sticky” and is hard to squeeze.

35. The amount of sand, silt, and clay tells us a story about the soil.

36. First, it tells us how much water can be stored in the soil.

37. Second, it tells us what kind of creatures lives in the soil.

38. Third, it tells us what kind of plants can grow.

39. Next, it tells us how deep plant roots can grow.

40. Then, it tell us how much water can pass through.

41. Finally, it tells us how the soil has changed over time.

42. Horizon Properties Soil Color Munsell Notation The Munsell code below each color in the GLOBE color chart is a universal notation that describes the soils’ color. 7.5 YR 4/3 The first set of number and letter symbols represents the hue. F Hue represents the position of the color on the color wheel (Y=Yellow, R=Red, G=Green, B=Blue, YR=Yellow Red, RY=Red Yellow).

43. Horizon Properties Soil Color (continued) Munsell Notation The Munsell code below each color in the GLOBE color chart is a universal notation that describes the soils’ color. 7.5 YR 4 / 3 The number before the slash is the Value. The number after the slash is the Chroma. F Value indicates the lightness of a color. The scale of value ranges from 0 for pure black to 10 for pure white. F Chroma describes how the “intensity” of a color. Colors of low chroma values are sometimes called weak, while those of high chroma are said to be highly saturated, strong, or vivid. the scale starts at zero, for neutral colors, but there is no arbitrary end to the scale.

44. Hue Value Chroma Horizon Properties Soil Color (continued) Munsell Notation Hue Value Soil Color Chart Pages Chroma

45. What is a “Ped?” A ped is a single unit of soil structure. A ped will vary with different types of soil.

46. Horizon Properties Soil Color (continued) 1. Take a ped of soil from each horizon and note on the data sheet whether it is moist, dry or wet. If it is dry, moisten it slightly with water from your water bottle. 3. Break the ped and compare the color of the inside surface with the soil color chart. 2. Stand with the sun over your shoulder so that sunlight shines on the color chart and the soil sample you are examining. Note: Sometimnes, a soil sample may have more than one color. Record a maximum of two colors if necessary, and indicate (1) the Main (dominant color) and (2) the Other (sub-dominant color).