Environmental Sciences: Towards a Sustainable Future Chapter 8

Soil and the Soil Ecosystem

SOILS (NOT DIRT!)SOILS (NOT DIRT!)A mixture of mineral particles and A mixture of mineral particles and

organic material that covers the land and organic material that covers the land and in which terrestrial plants growin which terrestrial plants grow

"A nation that destroys its soils destroys itself. Forests are the lungs of our land, purifying the air and giving fresh strength to our people." -- Franklin D. Roosevelt”

Why a Study of Soil Is Important 90% of the world’s food comes from

land-based agriculture. Maintenance of soil is the cornerstone

of sustainable civilizations. Simply stated, it is the “foundation” of

terrestrial life.

4 Components of Soils4 Components of Soils

Organic Materials (5%), key partOrganic Materials (5%), key part Air (25%)Air (25%) Water (25%)Water (25%) Minerals (45%): phosphate, nitrate, Minerals (45%): phosphate, nitrate,

potassium ions, calcium ions, etc.potassium ions, calcium ions, etc.

Soil FunctionsSoil Functions Anchors roots for plantsAnchors roots for plants Provide a storage for oxygen and water to plantsProvide a storage for oxygen and water to plants Provides habitat for nitrogen fixing bacteriaProvides habitat for nitrogen fixing bacteria Furnishes minerals for building and technologyFurnishes minerals for building and technology Buffers against pollutants getting into ground waterBuffers against pollutants getting into ground water Preserves a record of past environmental eventsPreserves a record of past environmental events Storage of large amounts of carbon (building block Storage of large amounts of carbon (building block

of life, but also keeps it from the atmosphere COof life, but also keeps it from the atmosphere CO22))

Golden Rules of Sustainable Agriculture Cover the soil Minimal or zero tillage Mulch for nutrients Maximize biomass production Maximize biodiversity

Global Trend: Where Did All the Farms Go? Poor farming practices = loss of soils

and farmland. Erosion Salinization

Development in United States = loss of 1.4 million acres of farmland per year.

Soil Profile

Soil Profile: Typical soils consist of 5 distinct layers. Why is Soil Profile: Typical soils consist of 5 distinct layers. Why is topsoil so important?topsoil so important?

Topsoil Formation

How are soils formed? CLORPTHow are soils formed? CLORPT

CLimate (provides sources of erosion)CLimate (provides sources of erosion) Organisms: flora and fauna (breaks Organisms: flora and fauna (breaks

down to provide nutrients) down to provide nutrients) Parent Material (must have starting Parent Material (must have starting

bedrock material to break down)bedrock material to break down) Relief or topography (affects the Relief or topography (affects the

retention of soil)retention of soil) Time (nutrients accumulate until they Time (nutrients accumulate until they

are at a stable place)are at a stable place)

Soil Texture Soil texture refers to the percentage of

each type of particle found in the soil. Loam soil is approximately 40% sand,

40% silt, and 20% clay.

Soil Texture Sand Silt Clay

Large

Small

Smaller

Soil Texture

“ribbon” test

Soil Texture and Properties

Texture Water Infiltration

Water-holding Capacity

Nutrient-holding Capacity

Aeration

Sand Good Poor Poor Good

Silt Medium Medium Medium Medium

Clay Poor Good Good Poor

Loam Medium Medium Medium Medium

Components that affect soil fertilityComponents that affect soil fertility Soil Structure (refers to how soil binds together, Soil Structure (refers to how soil binds together,

large clumps and air spaces can be good)large clumps and air spaces can be good) Water and Air InteractionsWater and Air Interactions Organic Material and Air InteractionsOrganic Material and Air Interactions AcidityAcidity Adsorption of ions = ion exhange capacity which Adsorption of ions = ion exhange capacity which

allow for binding to nutrients to prevent leaching allow for binding to nutrients to prevent leaching Chelates (organic soluble forms of essential Chelates (organic soluble forms of essential

minerals contribute to nutrient metal availability)minerals contribute to nutrient metal availability)

NutrientsNutrients Elements essential for plant growth include: Elements essential for plant growth include:

C, H, O, N, P, K, S, C, H, O, N, P, K, S, Ca, MgCa, Mg (macronutrients) (macronutrients) Fe, Mn, B, Zn, Cu, Cl, Co, Mo, Ni Fe, Mn, B, Zn, Cu, Cl, Co, Mo, Ni

(micronutrients)  (micronutrients)   All of these get cycled through the ecosystemAll of these get cycled through the ecosystem If these are missing, you miss them in your If these are missing, you miss them in your

diet! diet!

Soil Classes: arable land or not?? Mollisols: fertile soils with deep A

horizon; best agriculture soils; found in temperate grasslands like Colorado plains

Oxisols: iron and aluminum oxides in B horizon; little O horizon; Poor agriculture soils due to low organic matter on ground; tropical and subtropical regions, pineapple and banana plantations

http://forces.si.edu/soils/swf/soilorders.html for visuals

Soil Classes Alfisols: well-developed O, A, E, and B

horizons; suitable for agriculture if supplemented; temperature forest biomes

Aridisols: little vertical structure; thin and unsuitable for sustainable agriculture, lots of sand; susceptible to salination (due toover irrigation needs); deserts

Plant-soil-water Relationships

Productive Soil Good supply of nutrients and nutrient-

holding capacity Infiltration, good water-holding

capacity, resists evaporative water loss Porous structure for aeration Near-neutral pH Low salt content

Soil: IT’S ALIVE!

Humus Partly decomposed organic matter High capacity for holding water and

nutrients Typically found in O horizon

Humus: To Be or Not to Be

Desert PavementThe fine clay and silt is easily suspended and washed away, often ending up in floodplains or low spots, leaving desert pavement behind

Causes of Soil Degradation

Soil degradation Erosion is the proces of soil and humus particles

being carried away by wind or water Splash erosion (raindrops) Sheet erosion (small layers) Gully erosion (convergence of small gulleys, lots

of loss) Desertification (extreme deteriorization of arid

land due to loss of vegetation and soil moisture)

Soil Degradation

Prevention of Soil Erosion Change in attitude on national and

local level Federal programs encouraging

sustainable land use Focus of university agriculture

programs