Lecture #6 – Plant Nutrition and Soils

Image – a soil profile

Key Concepts:• Resources

Which are requiredHow they are used

• Essential elementsWhat they areWhat they do

• Soils and soil forming factors• The rhizosphere• Some alternate methods to acquire

nutrients

Resource requirements for plant growth???

Solar energy The sunCO2 The atmosphereO2

Water The soilNutrients

Where do plants get these resources???

Water The soilMineral Nutrients

Where do plants get these resources???

Water The soilMineral Nutrients

Diagram – plant resource requirements and sources

Image – root system of a grass

Plant tissue composition by weight:

• Fresh herbaceous tissue is 80-85% water• Little water is incorporated into plant tissue

What does water contribute to tissue???• Most water is in the cell solution, in the

vacuoles, or passing through in the transpiration stream

Critical Thinking

• Does wood have such a high percentage of water???

Critical Thinking

• Does wood have such a high percentage of water???

• Typically not – wood is dead tissue and xylem often becomes plugged up by resins, etc in the interior of the treeThis is what we call “heartwood” and it is often

very beautiful

What does water contribute to tissue???• Most water is in the cell solution, in the

vacuoles, or passing through in the transpiration stream

Water supplies all the H to carbohydrates; electrons and protons for photosynthesis

• Most water is in the cell solution, in the vacuoles, or passing through in the transpiration stream

Water contributes H to carbohydrates; electrons and protons for photosynthesis

• Most water is in the cell solution, in the vacuoles, or passing through in the transpiration stream

DRY plant tissue composition by weight:

• 45% carbon• 45% oxygen• 6% hydrogen• 5% inorganic mineral nutrients

Each a tad under 45%

• 45% carbon – from ?? CO2

• 45% oxygen – from ?? CO2

• 6% hydrogen – from ?? water• 5% inorganic mineral nutrients – from ??

• 45% carbon – from CO2

• 45% oxygen – from• 6% hydrogen – from• 5% inorganic mineral nutrients – from

• 45% oxygen – from CO2

• 6% hydrogen – from water• 5% inorganic mineral nutrients – from

Diagram – what goes into photosynthesis and what comes out

C, H, O – source and fate in photosynthesis

• 45% oxygen – from CO2

• 6% hydrogen – from water• 5% inorganic mineral nutrients – from soil

0.75-1% of wet weight, but many are essential to plant growth and function

Critical Thinking

• What is the difference between a chemical element, a molecule and a macromolecule???

Critical Thinking

• What is the difference between a chemical element, a molecule and a macromolecule???

• N vs. N2 vs. chlorophyll

Essential Elements• Chemical elements

Not molecules, though some are delivered in that form – N vs. NO3

• Required for growth and function of the plant• Can’t be replaced by some other element

• Some contribute to structural components• Some contribute to metabolic processes or

the maintenance of homeostasis

Essential elements in structural plant components:

• What are some essential molecules used in structural components???

• Cellulose – ??• Lignin – ??• Pectin – ??• Cell membranes – ??• Proteins (cell membrane, cytoskeleton) – ??

• Cellulose – C, H, O• Lignin – C, H, O, S• Pectin – C, H, O, Ca• Cell membranes – C, H, O, P• Proteins (cell membrane, cytoskeleton) –

C, H, O, N, sometimes S

Note – C H and O are in ALMOST ALL organic molecules

Essential elements for metabolic processes:

• What are some essential molecules used in metabolic processes???

• Chlorophyll – ??• Nucleic acids – ??• ATP – ??• Enzymes and other proteins – ??• Enzyme cofactors – ??• Elements that control water, charge and

solute balance – ??

• Chlorophyll – C, H, O, N, Mg• Nucleic acids – C, H, O, N, P• ATP – C, H, O, N, P• Enzymes and other proteins – C, H, O, N..S• Enzyme cofactors – many micronutrients• Elements that control water, charge and

solute balance – K, Cl, P, Ca, others

Note – C H and O are in ALMOST ALL organic molecules

Macro Nutrients vs. Micro Nutrients

• Nitrogen• Potassium• Calcium• Magnesium• Phosphorous• Sulfur

• Chlorine, Iron, Boron, Manganese, Zinc, Copper and Molybdenum

• Some plants also require Nickel, Sodium, Silicon, Selenium or others

All used in large quantities to support the structures and processes listed before

Mostly used in enzymes, as enzyme cofactors or in electron transfers – often reused, less required

Table – essential nutrients, both macro and micro

Study table in book!

Memory device in honor of my friend and mentor, Dr. Chuck Davey –

celebrated in 2006 for 50 years of service to soil science!!!

“C HOPKNS CaFe, Mg, Mn B CuZn Mo, Cl”

C. Hopkin's cafe, mighty good, managed by cousin Mo, waitress Clara

Nickel may also be essential

Images – various plants that use additional elements

Silicon in horsetails

Sulfur in mustards

Uranium in macadamia nuts

Some minerals required, some by chance…

Critical Thinking

• How do you tell which are required???

Diagram – a hydroponic experiment

Critical Thinking

• Hydroponics!

Critical Thinking

• Hydroponics!• How would elements NOT required

enter the plant tissue???

Critical Thinking• How do you tell which are

required???• Hydroponics!• How would elements NOT required

enter the plant tissue???• They are pulled toward the root in the

transpiration stream, and enter through any membrane channel they can fit through

Images – signs of deficiency

All plants will exhibit signs of deficiencies…..

Critical Thinking

• If the deficiency appears first in the older leaves, is that nutrient mobile or immobile???

Critical Thinking

• Mobile – it’s being translocated from the older tissues to the new, growing tissues

• How???

Critical Thinking

• Mobile – it’s being translocated from the older tissues to the new, growing tissues

• How???• In the phloem!!!

The older tissue acts as a sourceThe younger tissue is the sink

Mg deficiency in older leaves (mobile)

Fe deficiency in younger leaves (immobile)

Critical Thinking

• Why would some elements be mobile, and others not???

Critical Thinking

• Why would some elements be mobile, and others not???

• Must be soluble in water – phloem sap is water based…

• Some get locked into membranes or other components that can’t be broken down

Image – roots

Most plants get most of their nutrients from the soil – absorbed

through the roots

Soil is not just Dirt!

• Soil is the “skin” of the earth

• Soil provides for virtually all our food

• Soil supports the forests that maintain the hydrological cycle

• Soil supports virtually all terrestrial ecosystems – from micro-organisms to charismatic macro-fauna

Image – erosion after tropical deforestation

The results of deforestation are ecological, economic and social disaster ( )Rosie

Removing the plants removes the soil’s protective “blanket” and erosion is almost inevitable

More images – erosion

Erosion from deforestation in

Madagascar

Image – sediments from eroded land flooding out to sea

Sedimentation from erosion – this represents a huge loss of soil “capital”

Image – sediments eroding off Haiti into the sea

Sediments eroding off Haiti

Image – the political boundary is clear from the deforestation

Dominican Republic

Image – the drought in Haiti, where residents eat mud to survive

Haiti’s drought is caused largely by deforestation – the hydrological cycle has been snapped

Maps – deforestation in England and in the US

Deforestation in Warwickshire, England

Deforestation in the US

Map – soil loss in the Southern Piedmont of the US due to deforestation and abusive agricultural practices

Piedmont soil erosion in the

southeastern US

Image – eroded land in the Southern Piedmont

The USFS Calhoun Experimental Forest in the 1950’sUnion County, South Carolina

Maps – loss of farms, rise of industrial forestry, creating the biological deserts of pine plantations

Loss of soil (along with the boll weevil)

nearly eliminated productive

agriculture in the Southern Piedmont after the 1920’s – now most of the Piedmont is in industrial pine

plantations because it can no longer

support productive agriculture

Social

JusticeYou can help!!!

Compassionate Thinking

• What can you do to help???

Compassionate Thinking

• What can you do to help???• Give – time, money• Conserve – resources• Learn• Think• Talk• Activate – take leadership roles

• VOTE!!!!!

There are 3 R’s

A dynamic natural body in which plants grow, composed of mineral and organic materials, air, water,

and living organisms

Soil Forming Factors:

Parent MaterialClimate

Living OrganismsTopography

All soil forming factors interact!!!

Parent Material

• The substrate from which soil forms

• May be bedrock or some deposited material (sediments, organic material…)

• Determines soil texture, mineral content

• Influences soil structure and pH

71Igneous rocks form from molten rock

Sedimentary rocks form from deposited

materials

Metamorphic rocks form from igneous or sedimentary rocks that have been altered by heat and pressure

In the Charleston area, our soils form from unconsolidated Coastal Plain sediments

Critical Thinking

• Why???

Critical Thinking

• Why???• We were under water from ~ 140 mya to

less than 100,000 years ago

Sediments were deposited on top of the crystalline bedrock during all this time

Soil develops from what’s on top!

PM determines

soil texture = percentage of sand, silt and

Loam soils have ~ equal percentage of each texture

Clays are especially important• Tiny (<2um)

Huge surface area per unit mass (1000X more than same volume of sand)

• Typically platy in structure = vast additional internal surface area (800 m2/gm)

• Typically clay minerals carry a negative charge

Critical Thinking

• Why is a huge surface area of negative charge important to soil fertility???

Critical Thinking

• Why is a huge surface area of negative charge important to soil fertility???

• Many essential elements are in the soil solution in cation formClay particles hold these cations and limit

leaching• Water is also held (remember it’s polar)

Plus, smaller pore size holds more water

Most clays carry negative charge on both external

and internal surfaces

Cation Exchange – remember the root cap – protons displace cations

Texture also influences soil

moisture – clays hold onto more

Small pore size and negative

charge

Relationship between soil texture, field capacity and

water availability

Hands On• Determine soil texture• Take some soil from your jar and dampen

slightly – use the flow chart• Mix the soil with your hands – can you make

a firm ball of soil???• Can you make a ribbon of clay with your

fingers???• Rub a bit of soil between your fingers – can

you feel the grit of sand??? The powder of silt and clay???

Hands On

• Add water to your jar and shakeHave a ruler ready

• Set the jar down and mark the timeMeasure sediments after 40 seconds = sandMeasure again at 30 minutes = sand + siltRemainder is clay – we may have to wait until

tomorrow to get final measurementsDivide the depth of each layer by the total to get

percentage of sand, silt and clayUse textural triangle to determine soil texture

Parent materials

are weathered

by other soil forming

factors to form soil

Soils are typically

layered, in horizons,

because of downward movement of water, clays, etc

Critical Thinking

• Which soil horizon has the most biological activity???

• Why???O

Critical Thinking

• Which soil horizon has the most biological activity???

• The “A” horizon – the topsoil• Why???• More air, water and organic materials from

the surface

“A” Horizon

The topsoil is the most

biologically active horizon – more air, water

and organic materials from

the surface

Soil Profile – a cut that reveals the horizons

Climate

• Primarily temperature and precipitation patterns

• Temperature controls freeze-thaw cycles that contribute to physical weathering

• Temperature also affects the rate of biochemical reactions

• Temperature also affects the rate of decomposition by fungi, bacteria, and other living organisms

Climate

• Precipitation contributes to soil moisture, which affects plant growth and the activity of decomposing organisms

• Precipitation affects erosion (the physical loss of soil particles) and leaching (chemical losses from the soil solution as water passes through the soil – this contributes to profile formation)

Major biomes are determined by climate – microclimate is also important in soil development

Living Organisms

• Macro-organisms, including plants and animals

• Micro-organisms, including bacteria, fungi, single-celled “protists”, and micro-fauna

• Human activity typically results in abrupt and very negative changes to soil

Living Organisms – Plants• Contribute organic material – both from

above (shoots) and below (roots), and both sources affect horizonation

• Help to mix the soil – root channels, wind throws

• Cycle nutrients from soil to plant and back (sometimes through animals, always through decomposers)

• Help prevent soil erosion by breaking the force of rain, providing a litter layer

Same parent material will

develop into a different soil

under different plant communities

Critical Thinking

• Why are grassland soils so dark at the surface???

Critical Thinking• Why are grassland soils so dark at the

surface???• Organic material!• Grasses have a lot• of fine roots and very• quick root turnover• A lot of OM is• contributed

Living Organisms – Animals

• Contribute organic material when they die

• Contribute to nutrient cycling

• Help to mix the soil by burrowing, some even “eat” soil (earthworms)

Critical Thinking

• How do animals contribute to nutrient cycling???

Critical Thinking

• How do animals contribute to nutrient cycling???

• Plants absorb nutrients from the soil• Animals turn plant into animal• Dead animals (plus “excess” biomass)

return those nutrients to the soil via decomposing fungi, bacteria, etc

• Plants absorb nutrients from the soil…

Living Organisms – Micro-orgs• Decompose organic material, cycle

nutrients, add OM• Trillions/kg of soil (double handful of soil….)• N-fixing bacteria = supply virtually all N for

plant growth, either free living or in nodulethe nitrogen paradox….bacteria convert

atmospheric N to forms suitable for plant uptake• Mycorrhizae = mutual symbiotic association

between fungi and roots, present in most plants, required by some

Small animals, soil dwelling micro-fauna, fungi, bacteria, and other micro-organisms decompose dead

OM, cycling nutrients back into the soil

plant growth, either free living or in noduleThe nitrogen paradox….bacteria convert

N-fixing bacteria in symbiotic mutualisms, mostly with legumes

N-fixing bacteria in trees!

• Mosses on old-growth trees in the coastal Pacific Northwest forests host significant populations of N-fixing cyanobacteria

• Rain washes the nitrogen into the soil• Trees absorb from soil• Trees > 100 years old

Must be old for moss• Published 2011

http://www.sciencedaily.com/releases/2011/06/110607121144.htm

plant growth, either free living or in nodulethe nitrogen paradox….bacteria convert

Critical Thinking

• What do you think mycorrhizae might contribute to the symbiosis???

Critical Thinking

• What do you think mycorrhizae might contribute to the symbiosis???

• Surface area – LOTS

Mycorrhizae are symbiotic mutualisms between fungi and plants – fungal hyphae vastly

increase surface area for water and nutrient absorption – 85% of plants depend on them

Hands On

• Shake up class sample of soil / water to mix• Examine a drop of soil “solution” for

microorganisms

Living Organisms – The human impact

• Removing vegetation dramatically increases erosion, cultivation exacerbates

• Deforestation can snap hydrological cycles• Excessive fertilizer and pesticide use

contaminates both soil and water• Improper irrigation salinates soil• Wetland drainage damages wetland soils• and on….

Topography – the shape of the land

Topography – the shape of the land• Determines the movement of water, thus

affecting erosion and leaching rates• Determines where water accumulates, which

affects soil moisture, which affects organismal activity, which affects soils….

• Aspect affects the amount of solar radiation at the surface, and thus soil temperature

• Large topographic features influence precipitation patterns

• Even micro-topography influences plant distribution

Topographic Aspect – red and blue face S and W; green and

yellow face N and E

Critical Thinking

• Why are the north and east slopes of a hill cooler???

Critical Thinking

• Why are the north and east slopes of a hill cooler???

• The hill itself shades those sides

Orographic lifting makes it rain

Critical Thinking

• What the heck is orographic lifting and why does it cause rain???

Critical Thinking

• Orographic means that an air mass is being forced by wind to go up and over a mountain

Critical Thinking

• Orographic means that an air mass is being forced by wind to go up and over a mountain

• The air mass cools at higher elevations, condenses, and precipitation falls

Orographic lifting causes cooling and precipitation, rain shadow to the leeward

Small change in elevation…

…big change in the plant

community!

Images showing pond embedded within longleaf pine community

Hands On

• Let’s go outside for this one….• Trays of soil at different slopes to

demonstrate erosion x slope + erosion vs. leaching

• Pour water from same height and at same rate on different slopes

Time….

• The length of time all these factors have been acting determines the characteristics of the soil

• The same parent material will develop different soils as time passes

• Major component of primary succession

Soil development on glacial till

Soil Forming Factors:

Parent MaterialClimate

Living OrganismsTopography

Remember – all soil forming factors interact!!!

The RhizosphereThe area of interaction between root and soil.A huge volume of soil, but a very narrow zone

The rhizosphere is the zone of cation exchange, nutrient and water uptake

The Rhizosphere

• Complex zone with many interacting factors• Plant affects soil through compounds

secreted by the plant’s roots• Relative proportions of nutrients in the soil

solution can affect uptake of all nutrients• Also, different species have different

nutrient requirements• Rhizosphere is the control zone for

plant/soil interactions

Some plants use alternate methods to absorb some nutrients

• Parasites, saprophytes, carnivores

Key Concepts: QUESTIONS???• Resources

Which are requiredHow they are used

• Essential elementsWhat they areWhat they do

• Soils and soil forming factors• The rhizosphere• Some alternate methods to acquire

nutrients

Hands On

• What can you tell from this data???

Extra Credit

• Putz around on the USDA soils site• http://

soils.usda.gov/education/resources/college/index.html

Lecture #6 – Plant Nutrition and Soils

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