How do soils form? Processes 5.1 Introduction to soil systems The soil system is a dynamic ecosystem that has inputs, outputs, storages and flows How do soils form? Processes List the processes that occur in a soil? Give an example of each Additions – rain adds water, dust adds minerals, as plants die and animals poop organic mater is added, humans also add fertilizer Losses – evaporation, nutrient up take, leaching of nutrients and elements Translocations – gravity pull water and dissolved materials down, OM can move in many directions due to critters, clay movement, eluviated horizon Transformations – decomposition, weathering, iron rusting (reddening) or dissolving (graying), clay formation Describe how a soil will change with time. OM accumulates A horizon forms Horizons get thicker May get redder if well drained or get grayer if wet E horizon becomes more evident

4 basic processes in the soil ADDITIONS LOSSES TRANSLOCATIONS Four basic processes. Ask students to come up with more examples for each as each is discussed in the next 4 slides. (MOVEMENT WITHIN THE SOIL) TRANSFORMATIONS (ONE COMPONENT CHANGES TO ANOTHER)

ADDITIONS Rain adds WATER. Dust adds MINERALS. Animal waste add ORGANIC MATTER and NUTRIENTS. Humans add FERTILIZER. Materials can be added to the soil in many ways. Natural ways include rainfall, dust settling, animal wastes, tree leaves in the fall etc. Humans add wastes as well as fertilizer.

LOSSES WATER evaporates into the air. Soil particles WASH AWAY in storms. ORGANIC MATTER may compose into carbon dioxide. NUTRIENTS and MINERALS leach into groundwater or are taken up by plants. Losses are removal of components from the soil profile. Leaching can first translocate components deeper in the profile but in extreme cases where the component is removed it is referred to as a leaching loss. Erosion is another example of a loss. Decomposition can both transform (organic material to humus) and cause a loss (organic matter to carbon dioxide which then moves to the atmosphere)

TRANSLOCATIONS GRAVITY pull WATER down from top to bottom. MOVEMENT WITHIN THE SOIL GRAVITY pull WATER down from top to bottom. EVAPORATING WATER draws minerals up from bottom to top ORGANISMS carry materials every direction. Translocation is moving components within the soil profile but not leaving the profile Movement is often due to water flow by gravity. Water moves minerals, nutrients, and organic matter. If these materials leave the profile it is a loss. So Loss can begin with simple translocation. Movement is not always down as evaporation can cause minerals dissolved in water to move upwards. An example is salts on the surface of some desert or drier soils.

TRANSFORMATIONS Dead leaves decompose into HUMUS. (ONE COMPONENT CHANGES TO ANOTHER) Minerals in rock weather to clay Rocks break in to smaller pieces Iron in minerals turns to rust (iron oxides) Leaves decompose to humus Dead leaves decompose into HUMUS. Hard rock WEATHERS into soft clay Oxygen REACTS with iron, “rusting” the soil into a reddish color.

Looks Change With Age Soil is constantly changing due to the 4 processes. This means soil is dynamic –in a constant state of change. This diagram may help understand better how the processes affect the soil. The older a soil gets, the more different it looks from its parent material. Soil is always changing – minerals, water, air, organic matter and organisms – always change.

A - topsoil E-Eluviated B- Subsoil C-Parent Material R- Bedrock 10 100 1,000 10,000 100,000 AGE IN YEARS A soil profile is like a snap-shot, capturing what the soil looks like NOW. In the PAST, soil looked different, and in the FUTURE, it will look different then it does now. The soil changes as a result of the process acting upon it. In a very general sense this diagram shows how the soil changes over time. Note that a well developed soil profile will have more and thicker horizons than a less developed soil profile.

Why is Soil Important? Ultimately responsible for all the food we consume. Provides all nutrients for producers Habitat for many organisms Filters water Recycling nutrients (home to many decomposers and detritivores) so that chemical cycles can occur

What is Soil Made from? Rock Particles – from parent rock material Made of gravel, sand, silt, clay, and chalk Contains minerals Humus - Organic matter made from the decomposition of living things Results in nutrients and minerals returning to soil Absorbs and retains water Water – held in spaces between soil Dissolves minerals and allows movement through soil and uptake by plants (rapid movement of mineral salts can lead to salinization) Too much water can lead to anoxic conditions and acidification Air – held in soil grains Well aerated soil provides oxygen for soil organisms and plant roots Soil Organisms – mostly invertebrates but can be things such as moles Break down large particles (detritivores) Decompose – recycling minerals and nutrients Mix and aerate soil (eg moles, prairie dogs, naked mole rats)

How Does Soil Form?

How Does Soil Form? Very Slow Process Weathering of rock (mechanical) Deposition of sediments by erosion (mechanical) Decomposition of organic matter (chemical)

System Diagram Construct a system diagram of the following data: Storages Organic matter, organisms, nutrients, minerals, air, and water Transfers within soil Biological mixing (organism living in soil mix nutrients & minerals in with organic matter), translocation (movement of soil particles in suspension, Inputs Organic material including leaf litter, inorganic matter from parent rock, precipitation, energy Outputs Uptake by plants, soil erosion Transformations Decomposition, weathering, nutrient cycling

System Diagram Inorganic Matter Water Air Minerals Weathering Nutrient Cycling Minerals Weathering Respiration Biological Mixing SOIL Nutrients Nutrient Cycling Biological Mixing Ecosystem Litter Organis ms Organic Matter

Soil System Food Web

Cycle Review

Cycle Review

Vocabulary Transform Weathering Decompose Leaching Minerals Organic Matter Organisms Developed Soil Humus Bedrock

Vocabulary Additions Losses Translocation These words are not defined in Soil! Get the Inside Scoop but are defined below. Additions – to add material or substance to the soil Losses – to remove material or substance from the soil Translocation – to move material or substance within the soil without adding or removing anything