1. General Soil Information

2. Definition of Soil
Soil – relatively thin surface layer of the Earth’s crust consisting of mineral and organic matter that is affected by agents such as weather, wind, water, and organisms.
Dynamic membrane that covers earth’s surface
Connects biological and geological world

3. Ecosystem Services Provided by Soil

4. Importance of Soil
Organisms, mainly microorganisms, inhabit the soil & depend on it for shelter, food & water.
Plants anchor themselves into the soil, and get their nutrients and water.
Terrestrial plants could not survive without soil, therefore, humans could not exist without soil either.

5. SOIL: A RENEWABLE RESOURCE
Soil is a slowly renewed resource that provides most of the nutrients needed for plant growth and also helps purify water.
Soil formation begins when bedrock is broken down by physical, chemical and biological processes called weathering.
Mature soils, or soils that have developed over a long time are arranged in a series of horizontal layers called soil horizons.

6. Major Components of Soil
Pore Space (50%)
This may contain air and/or water
Soil Space (50%)
Organic Matter
Mineral Matter

7. Soil Formation & Parent Material
The rock that has slowly broken down into smaller particles by biological, chemical, and physical weathering.
To form 2.5 cm (1 in.) it may take from years.

8. Soil Properties: Texture
The percentages (by weight) of different sized particles of sand, silt and clay that it contains.
For Example: a soil has 24% clay, 41% silt, and 35% sand. The soil is classified as:
Medium loam

9. Texture Largest → Smallest Sand → Silt → Clay
>2mm in diameter = gravel/stones (not actually considered soil because it doesn’t have direct value to plants.
0.05 to 2mm = sand (the largest soil particles) can be seen easily with the eye.
0.002 to 0.05mm = silt – about the size of flour and barely visible with the eye.
<.002mm = clay (has the greatest surface value) – only seen under and electronic microscope.

10. Texture: The Ribbon Test
To tell the difference in soil, take the soil, moisten it, and rub it between your fingers and thumb.
Gritty -has a lot of sand
Sticky- high clay content and you should be able to roll it into a clump
Silt- smooth, like flour.

11. Physical Properties of Soils
Texture: the amount of sand silt, and clay
Structure: How soil particles are organized and clumped together. (Sand, silt, clay)
Friability: How easily the soil can be crumbled
Porosity: A measure of the volume of soil and the average distances between the spaces

12. Permeability
The rate at which water and air moves from upper to lower soil layers. It is distances between those spaces.
Why does soil need air spaces?
Aerobic microorganisms need oxygen for cellular respiration!
Can increase the water holding capacity of a soil by adding clay

13. Shrink-Swell Potential
Some soils, like clays, swell when H2O gets in them, then they dry and crack. This is bad for house foundations, etc.
Important for builders to know

14. C HOPKN’S CaFe Mg B Mn Cu Zn Cl Mo
Soil Nutrients
C HOPKN’S CaFe Mg B Mn Cu Zn Cl Mo
Macronutrients: larger in atomic structure.
Plants need them in large amounts
Ex. Nitrogen, Phosphorus & Potassium.
Micronutrients: smaller in atomic structure. Plants need them in small amounts. Ex. Selenium, Zinc & Iron

15. pH The pH of most soils ranges from 4.0 to 8.0.
Plants are affected by pH because of the solubility of nutrient minerals.
At a pH of 4.5, N, P, K, S, Ca, Mg are not very available to plants
At a pH of 4.5, Fe, Mn, and Al are very available to plants and they are toxic to plants in high amounts
Easy and inexpensive way to make an acidic soil more basic is to add crushed limestone (to fields) or egg shells to small gardens or house plants
Inexpensive way to make Azalea beds more acidic is to add coffee grounds or pine needles or pine bark to the beds

16. Climate and Soils Probably the most important factor
soils produced from the same parent material under different climates will have different properties
Climate governs the rate and type of soil formation
Main determinant of vegetation distribution.
Soil climate has two major components;
moisture (precipitation) and temperature, influencing evaporation.
When precipitation exceeds evaporation, leaching of the soil will occur.
Temperature determines the rate of reactions:
Chemical and biological decay
Influences weathering of soil

17. Soil Horizons
A horizon
B horizon
C horizon

18. Soil Horizons O: Organic Horizons
Organic Layers of Decaying Plant and Animal Tissue (detritus)
Aids Soil Structural Development
Helps to Retain Moisture
Enriches Soil with nutrients as the leaf litter decomposes
O Horizon
Desert soils do not have O horizon; no leaf litter
Dark in Color Because of Humus Material - 1,000,000 bacteria per cm3

19. Soil Horizons: A Horizon or “ Topsoil”
It is dark and rich in accumulated organic matter and humus.
It has a granular texture and is somewhat nutrient-poor due to the loss of many nutrient minerals to deeper layers and by leaching.
Humus: A dark-brown or black organic substance made up of decayed plant or animal matter.
A Horizon
Grasslands and forests have deep A horizons (lots of humus which increases water holding capacity

20. Soil Horizons: E Horizons
Mineral Horizon Near Surface
Movement of Silicate Clay, Iron, and Aluminum from the A Horizon through Eluviation
Eluviation: movement of materials suspended through a soil
Horizon does not mean a water table is present, but the horizon can be associated with high water table
E Horizon

21. Soil Horizons: B Horizons Zone of Maximum Accumulation
The light-colored subsoil beneath the A-horizon
often a zone of illuviation where nutrient minerals have leached out of the topsoil and litter accumulate
Typically rich in iron and aluminum compounds and clay.
B Horizon

22. Parent Material (C-horizon)
Contains weathered pieces of rock & borders the un-weathered solid parent material. Most roots do not go down this deep and it is often saturated with groundwater.

23. Layers in Mature Soils
Infiltration: the downward movement of water through soil.
Leaching: dissolving of minerals and organic matter in upper layers carrying them to lower layers.
The soil type determines the degree of infiltration and leaching.

24. Fertilizers and Labels
N – P – K
12 –
Organic Fertilizers – animal manure, crop residues, bone meal, and compost
Inorganic Fertilizers – man-made from chemical compounds
Benefits – exact compositions are known; they are soluble & thus immediately available to the plant
Costs – quickly leach away; this pollutes the water; doesn’t help the water holding capacity of the soil like organic fertilizers do