BELL RINGER What makes up soil? (name at least 3) Why is soil important to humans? (name two reasons) What is the average thickness of topsoil? 1

2 Introduction to Soils The most important natural resource around the earth!

3 What is Soil? Defined as: Mineral & organic material that supports plant growth on the earth’s surface Mixture of particles of rock, organic materials, living forms, air, water

4 What soil resources help in supporting life? Oxygen: needed for adequate root growth Temperature: soil absorbs heat from the sun – loses heat to atmosphere (plant growth and seed germination) Water: plant growth Carbon: organic matter Minerals: nutrients and physical makeup

5 How is Soil Made? 1.All soil starts as rocks. 2.Powerful forces act on the rocks to break them into smaller fragments. 3.Water penetrates the cracks in the rock and when it freezes the water acts as a wedge to split the rock.

6 Soil origin cont. 4.Rivers, glaciers, landslides and avalanches cause rock particles to grind against each other wearing them down. 5.Chemicals mix with water to further break the rocks down. 6.Plants began to grow in the weathered rocks and as they die, they add organic matter to the soil which attracts soil micro-organisms.

7 Soil origin cont. 7.When this happens, then the soil is capable of supporting plant life and can then truly be called soil.

8 What does the Term Weathering Mean? Weathering is the processes that occur to break down rock into soil. This process includes water freezing, thawing, landslides, wind and chemical action.

9 What is Parent Material? Rock material that has undergone some weathering and change, but not enough to be called true soil, as it is not capable of sustaining plant life.

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11 List the 5 factors responsible for soil development. 1.Parent material 2.Climate 3.Variation in the earth’s surface (topography) 4.Plant & animal life 5.Time

Parent Material Parent rock from which a soil is formed has a significant effect on its qualities. Parent materials influence the formation of soils by their rates of weathering, the nutrients that they supply, and the particle sizes that they contain. The less developed a soil is, the more influence that the parent material has on its characteristics. 12

Climate Climate is a dominant factor in the formation of soils. The major components of climate that affect soil are precipitation and temperature. With low rainfall an accumulation of lime may occur,so these soils are usually alkaline. In areas of high rainfall there is intense weathering and leaching resulting in acid soils. 13

Climate continued Climate also has an indirect affect on soils by its action on vegetation. Changes in temperature affect the rate of physical/chemical weathering. Rates of chemical reactions increase as temperature increases, if sufficient water is also present. 14

Topography Topography (the lay of the land) influences drainage and runoff. Soil layer on gentle slopes will be generally deeper, sustain more luxuriant vegetation, and contain more organic matter than soil profiles on steeper slopes. In our hemisphere, mountains often affect the climate and in turn the soil. The western side of a mountain range often receive more rain and have more developed soil vs. the drier east side of a mountain. 15

Living Organisms The activity of living plants and animals (macro and microorganisms) has major significance on the development of soil. Microorganisms help develop soils by decomposing organic matter and forming weak acids that dissolve minerals faster than would pure water. Fibrous root systems of grasses have a distinctly different effect on soils than do the coarser roots of trees. Lichens, which are a combination of algae and fungi, are often the first plants that grow on weathering rocks. 16

Time It requires time, up to about a million years, to form soils. Rocks like granite are extremely hard to decompose. Softer rocks such as limestone take less time. As soils age they differentiate into defined profiles consisting of three different layers (A horizon, B horizon and C horizon). Horizons tend to develop faster under humid, warm, and forested conditions. A recognizable soil profile may develop in as few as 200 years or, under less favorable conditions, take several thousand years to develop. 17

Soil Development Over Time 18

19 Components of Soil Mineral Matter: about 45% of soil (partially decomposed rock material (sand, silt, clay) Organic Matter: about 5% of soil (partially decomposed plant & animal matter) Air: about 25% of soil (constant fluctuation as soil is dry and wet) Water: about 25% of soil

20 Plants use soil A.Anchorage – roots hold plant in place B.Water – absorbed through roots C.Oxygen – all living organisms need oxygen -good soil aeration needed for below ground plant parts to get oxygen D.Nutrients – roots take in the macro and micronutrients necessary for plant growth

21 Living Organisms in the soil Forms of life: –Earthworms –Insects –Bacteria –Fungi –Other organisms

22 Bacteria & Fungi Jobs Break down organic matter and release nutrients

23 Earthworm & other soil organism jobs Improve soil tilth –Ease at which soil can be worked –Create openings in soil as they tunnel –Enhances drainage and improves air exchange

24 Soil uses in agriculture Cropland Grazing land Forest Water structures (impoundments, retaining ponds) Agriculture depends on soil to grow food, fiber, and ornamental plants.

25 Nonagricultural uses of soil Recreation: playgrounds, sports fields, jogging paths, golf courses, parks, campgrounds Foundations: buildings have to have solid base Waste Disposal Building materials