Soil and the Soil Ecosystem 1

Why Study Dirt? 90% of the world’s food comes from land based agriculture 22% of the land used for crops, grazing, and forestry has become degraded during the past fifty years (See Table 8-1 p.187). 2

http://www. globalchange. umich http://www.globalchange.umich.edu/globalchange2/current/lectures/land_deg/concern.gif 3

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Areas of the planet threatened by soil erosion 6

Loss of Farmland to Development is Something We Experience Locally 7

No healthy topsoil = No us. 8

Add to this air, water, soil nutrients, salts, and pH. What is Healthy Soil? Add to this air, water, soil nutrients, salts, and pH. 9

Soil Formation—Mineral Soil Soil building begins with the physical and chemical fragmentation of the Parent Material. Mechanical Weathering Temperature change Abrasion Chemical Weathering Acid deposition Oxidation Type of parent material and the climate determine the type of mineral soil. 10

Soil Formation—Detritus Detritus is Decaying plants and animals. Supplies nutrients for plants Lowers soil pH Makes inorganic nutrients available to plants by increasing their solubility Typical range pH 6-8. 6-6.5 optimum for biological activity in most soil ecosystems. Creates a loose texture that increases aeration and water infiltration / water holding capacity. 11

Soil Formation—Detritus Optimum organic matter content for most non- wetland soil ecosystems is 3-5% Detritus that has undergone most of its decomp. Is referred to as humus humus-detritus that has been almost completely digested by the detritus feeder food web. humus will decomp @ 2%-5% of vol./yr. 12

Soil Formation—Detritus Food Web Microflora (the decomposers) help to unlock the nutrients stored in detritus and make them available to the rest of the DFW. Burrowing animals aerate the soil and mix the organic and inorganic components of the soil. 1 ha of healthy soil may contain 500k earthworms that can process 9 metric tons (20 k lbs) of soil/year. See handout for other denizens of the soil 13

Bacteria are the most important organisms in the detritus food web Bacteria are the most important organisms in the detritus food web. They are the first heterotrophs in any food chain. 15 tons/ acre 14

Rate of Topsoil Formation Varies depending on the conditions of the area, but primary sources list a range from 1” every 50 to 500 years. That’s a long time to wait for a meal. 15

Soil Characteristics Soils differ greatly from one area to another. Even on relatively small plots of land, soil types may differ. Soils are generally studied according to their Profile Texture Structure Color 16

Soil Profile page 188 17

Soil Texture Page 189 18

Soil Texture Sand are the largest particles and they feel "gritty." Silt are medium sized, and they feel soft, silky or "floury." Clay are the smallest sized particles, and they feel "sticky" and they are hard to squeeze. 19

Loam is common and generally considered ideal for plant growth. Properties of Soil Particles Worth Noting: large particles have large spaces separating them small particles have a larger surface area to volume ratio Nutrient ions and water molecules cling to surfaces Workability (Tilth)-the ease with which a soil can be cultivated 20

Soil Consistence Loose Friable Firm Extremely Firm Source 21

Soil Structure Prismatic: Vertical columns of soil that might be a number of cm long. Usually found in lower horizons. Blocky: Irregular blocks that are usually 1.5 - 5.0 cm in diameter. Granular: Resembles cookie crumbs and is usually less than 0.5 cm in diameter. Commonly found in surface horizons where roots have been growing. Single Grained: Soil is broken into individual particles that do not stick together. Always accompanies a loose consistence. Commonly found in sandy soils. Platy: Thin, flat plates of soil that lie horizontally. Usually found in compacted soil. 22

Soil Structure Columnar: Vertical columns of soil that have a salt "cap" at the top. Found in soils of arid climates. Massive: Soil has no visible structure, is hard to break apart and appears in very large clods. 23

Soil Structure Soil Structure-the “feel” of the soil (clumpy, soft, loose, etc.) Soil Structure vs. Soil Texture 24

Soil Color Quantified by horizon and inclusions using the Munsell Soil Color Charts. 25

Soil Color 26

Soil and Plants Plant considerations pertaining to soil: nutrients water air pH salinity These factors together affect the fertility “tilth” of the soil. 27

Nutrients Nitrogen (N2, NO3-, NO2-, NH3) Phosphate (PO43- ) Potassium (K+)  Calcium (Ca2+) These are added to the soil by weathering of parent material, fixation by bacteria from the atmosphere, and through decomposition of detritus. 28

Nitrogen Needed for chlorophyll synthesis. Leafy growth above ground. Hasten maturity of crops. Enhance fruit development. Optimum amounts present in soil depend 29

Phosphorus Encourages cell division Encourages root development 50 – 75 lbs / acre typically available to plants for growth. 30

Potassium Enhances disease resistance Activates enzymes needed for development Cuticle development Regulates turgor pressure Necessary for protein metabolism 31

Other Soil Properties leaching nutrient-holding capacity ion-exchange capacity Organic vs. Inorganic Fertilizer 32

Water Infiltration Water Content What it is Why it matters How to measure it Water Content 33

Water Water Holding Capacity Evaporative Water Loss What it is Why it matters How to measure it Evaporative Water Loss 34

Air the ability of the underground organs of plants to exchange gases with the outside environment is essential for their survival. Roots need air to grow. Many things affect the aeration of soil. mineral particles OMC Actions of Detritus Feeders and other animals Actions of plants Weather 35

pH from water from detritus from mineral soil evaporative qualities 36

Salinity Plants must maintain an osmotic balance with their external environment. addition of salt to the soil prevents plants from taking up water into their roots 37

Soil As an Ecosystem Nebel p.192 38

Loss of humus in topsoil is called mineralization There is an 85% to 95% decline in GPP when plants are grown on subsoil compared to when they are grown on topsoil. Loss of humus in topsoil is called mineralization 39

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