Environmental Sciences: Towards a Sustainable Future Chapter 8 Soil and the Soil Ecosystem

SOILS (NOT DIRT!) A mixture of mineral particles and organic material that covers the land and in 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 Soils Organic Materials (5%), key part Organic Materials (5%), key part Air (25%) Air (25%) Water (25%) Water (25%) Minerals (45%): phosphate, nitrate, potassium ions, calcium ions, etc. Minerals (45%): phosphate, nitrate, potassium ions, calcium ions, etc.

Soil Functions Anchors roots for plants Anchors roots for plants Provide a storage for oxygen and water to plants Provide a storage for oxygen and water to plants Provides habitat for nitrogen fixing bacteria Provides habitat for nitrogen fixing bacteria Furnishes minerals for building and technology Furnishes minerals for building and technology Buffers against pollutants getting into ground water Buffers against pollutants getting into ground water Preserves a record of past environmental events Preserves a record of past environmental events Storage of large amounts of carbon (building block of life, but also keeps it from the atmosphere CO 2 ) Storage of large amounts of carbon (building block of life, but also keeps it from the atmosphere CO 2 )

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 topsoil so important?

Topsoil Formation

How are soils formed? CLORPT CLimate (provides sources of erosion) CLimate (provides sources of erosion) Organisms: flora and fauna (breaks down to provide nutrients) Organisms: flora and fauna (breaks down to provide nutrients) Parent Material (must have starting bedrock material to break down) Parent Material (must have starting bedrock material to break down) Relief or topography (affects the retention of soil) Relief or topography (affects the retention of soil) Time (nutrients accumulate until they are at a stable place) Time (nutrients accumulate until they 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 TextureWater Infiltration Water- holding Capacity Nutrient- holding Capacity Aeration SandGoodPoor Good SiltMedium ClayPoorGood Poor LoamMedium

Components that affect soil fertility Soil Structure (refers to how soil binds together, large clumps and air spaces can be good) Soil Structure (refers to how soil binds together, large clumps and air spaces can be good) Water and Air Interactions Water and Air Interactions Organic Material and Air Interactions Organic Material and Air Interactions Acidity Acidity Adsorption of ions = ion exhange capacity which allow for binding to nutrients to prevent leaching Adsorption of ions = ion exhange capacity which allow for binding to nutrients to prevent leaching Chelates (organic soluble forms of essential minerals contribute to nutrient metal availability) Chelates (organic soluble forms of essential minerals contribute to nutrient metal availability)

Nutrients Elements essential for plant growth include: Elements essential for plant growth include: C, H, O, N, P, K, S, Ca, Mg (macronutrients) C, H, O, N, P, K, S, Ca, Mg (macronutrients) Fe, Mn, B, Zn, Cu, Cl, Co, Mo, Ni (micronutrients) Fe, Mn, B, Zn, Cu, Cl, Co, Mo, Ni (micronutrients) All of these get cycled through the ecosystem All of these get cycled through the ecosystem If these are missing, you miss them in your diet! If these are missing, you miss them in your 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 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 Pavement The 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