soil resources and sustainable agriculture soil is more than ‘dirt’ soil has 4 major components...

Soil Resources Soil Resources and Sustainable and Sustainable

AgricultureAgricultureSoil is more than ‘Dirt’Soil is more than ‘Dirt’

Soil has 4 major componentsSoil has 4 major components

Soil is dynamicSoil is dynamic

I. Soil DefinedI. Soil DefinedA collection of natural bodies, which has A collection of natural bodies, which has

been synthesized in profile form, from a been synthesized in profile form, from a variable mixture of broken and weathered variable mixture of broken and weathered materials and decaying organic matter, materials and decaying organic matter, which covers the earth in a thin layer and which covers the earth in a thin layer and which supplies, when containing the which supplies, when containing the proper amounts of air and water, proper amounts of air and water, mechanical support and sustenance for mechanical support and sustenance for plants.plants.

I. Soil DefinedI. Soil DefinedYoung soil is rich in silicon, iron, and Young soil is rich in silicon, iron, and

aluminum (ex. Volcanic)aluminum (ex. Volcanic)Old soil is devoid of nutrients through Old soil is devoid of nutrients through

leaching by rainwater (ex. Tropics)leaching by rainwater (ex. Tropics)

II. What is Soil? A. General Information

The 4 major components of the soil include Parent material (mineral materials) – 2 types primary

minerals and secondary minerals Primary minerals are the same as the parent material Secondary minerals have changed chemically, due to

weathering (i.e. oxidation and reduction) Organic materials – dead and decaying plant and animal

materials Primary source of Carbon and Hydrogen Sole source of usable Nitrogen Primary source of P and S Increases the amount of water soil can absorb


Water – The amount of water in the soil is dependant on many factors, but is the driving force for nutrient uptake, and yes, plants CAN drown!

Air – The source of oxygen for soil organisms, also dissolves into the water for use by plants, also oxidizes materials for removal from soil particles


Percent of each component differ with soil texture and soil type (defines the soil)

The greater the distance away from the surface of the soil, the smaller the particles and pore spaces.

Tends to have more minerals and water

II. What is Soil? B. Renewable Resource

Can be replenished and renewed indefinitely Agriculture removes nutrients, exposes soil to

the wind and rain (erosion) Topsoil accumulates at 10 tons per hectare (2.3

acres) About 1mm deep over the entire area (hectare)

II. What is Soil? C. Soil composition

About ½ of the soil is mineral Minerals are derived from parent material or

glacier deposits Particle size and the space between the particles

(pore size) affect soil characteristics

Soil Particle Classification Table Classification Gravel Sand Silt Clay

Particle Size Greater than 1mm 0.05 to 1mm 0.002 to 0.05 mm Less than 0.002 mm

II. What is Soil? C. Soil composition (cont.)

Organic content of soil varies Ex. 100% OM = Peat soil

Organic material is called humus Humus coats soil particles and holds them

together Maintains space between the particles for root

development Allows for water entrapment

II. What is Soil? D. Soil Organisms

Required for healthy soil Stay close to the surface Can be thousands of species and billions of

individuals per hectare Algae and blue-green bacteria convert light into

sugar Chemosynthetic bacteria convert sulfur into sugar

in anoxic areas

II. What is Soil? D. Soil Organisms (cont.)

Bacteria and fungi decompose organic matter Actinomycetes is the bacteria responsible for the

‘smell of dirt’, otherwise dirt (soil) would have no odor

II. What is Soil? E. Soil Profiles

Soils have layers Called horizons

Each layer gives information about the history of the soil

The type of soil is determined by the number, thickness, and type of layers it contains

Soil has other characteristics used in the field to identify soil profiles

II. What is Soil? E. Soil Profiles (cont.)

Thickness Color Texture Composition

A cross section of soil, showing the horizons, is called a Soil Profile

II. What is Soil? E. Soil Profiles (cont.)

A soil horizon is a defined soil layer within a soil profile

Examples of soil horizons are O, A, I, E, B, C, R Each example has different properties and

characteristics

Soil Horizons

Soil Horizons Organic matter: called the O horizon

Soil Horizons

• Top Soil: called the A Horizon

Soil Horizons Zone of leaching:

called the E horizon Also called the zone of

elluviation

Soil Horizons Zone of Collection: called the upper B horizon

Soil Horizons Weathered Parent Material: called the C horizon

Soil Horizons Bedrock: called the R horizon

II. What is Soil?

F. Soil Types Soil classification is based on profile and other

characteristics Structure and composition Classified into

Orders Suborders Great groups Subgroups Families series

II. What is Soil? Some of the major soil orders include

Alfisols: soils of deciduous forests, relatively fertile, medium brown, rich in aluminum and iron.

Aridisols: middle ages soils of dry regions, pale colors, sandy low in organic material

Entisols: young soils of dry or cold regions, pale colors, sandy, low in organic material

Histosols: very young organic peats and mucks, dark brown to black, often acidic

Inceptisols: young soils of arctic regions and mountain areas only slightly weathered

II. What is Soil? Mollisols: soft, crumply, dark soils formed under

grass, high organic content. Oxisols: soils of the warm, moist tropics, highly

weathered, thin, acidic, infertile surface layers. Spodosols: young, acidic soils of cool, moist

conifer forests, underlain by a pale, ash- colored layer

Ultisols: very old, nutrient-poor soils of mountains and other highly weathered areas.

Vertisols: middle aged, clayey soils, crack when dry, swell when wet.

Order: Alfisols

Order: Aridisols

Order: Entisols

Order: Histisols

Order: Inceptisols

Order: Mollisols

Order: Oxisols

Order: Spodosols

Order: Ultisols

Order: Vertisols

III. Soil Characteristics A. Flocculation

1. Refers to the formation of groups of soil particles

2. Caused by a net attractive force 3. Precursor of stable soil structures 4. Creates aggregate soil particles

a. Aggregation allows for fine textured soils to have large enough pores for proper aeration and water movement

III. Soil Characteristics A. Flocculation

Air and water movement through small pores will be very slow

B. Dispersion 1. Refers to the mutual repulsion between

particles 2. Caused by a net repulsive force

Flocculation and Dispersion

III. Soil Characteristics C. Net Forces Between Particles

1. Affected by properties of particles as well as the chemical environment

a. Chemicals available in the environment for plants are in the soil solution

b. Water solution plus the ions dissolved in it, is called the soil solution


2. The interaction of soil particles and soil solution determines whether the soil is flocculated or dispersed

a. Exchangeable ions, electrolyte concentrations and soil pH add to the condition of the soil


3. Soil particles are commonly negatively charged

a. Cations surround the particles to neutralize the charge

b. They are considered “exchangeable” cations The cations will change with changes in ion

concentrations Solid particle surface plus the cloud are called a double

layer


b. They are considered “exchangeable” cations (cont)

The thicker the double layer the greater the net repulsion between particles

Like repels like Creates dispersion

Thin clouds allow particles to be closer allowing for Van de Waals (water potential) forces

Creates flocculation


4.Cations are exchanged in the cloud based on Coulomb's Law ("The force of attraction or repulsion between two point charges is directly proportional to the product of magnitude of each charge and inversely proportional to the square of distance between them“)

a. Thus dispersion will favor exchangeable cations with i) low charge and ii) large size

b. Common cations in soil solution are Na+, K+, NH4

+, Ca 2+, Mg2+, and various forms of aluminum (Al3+)


5. Exchangeable cations will diffuse away from the particle surface based on the concentration gradient between surface and bulk solution increases

a. If the concentration of cations at the particle surface are high

A low solute concentration of cations in bulk solution will result in a large concentration gradient and a thick double layer (favor dispersion)


A high concentration of cations in bulk solution will result in a small concentration gradient and a thin double layer (favors flocculation

b. There is an affinity gradient Al3+ > Ca2+ > Mg2+ > NH4+ > K+

> Na+ (adsorption) 6. Soil particle charge can change based upon soil pH

Low pH creates a positive charge (adsorption of H+) High pH creates a negative charge (adsorption of OH-)

Net Forces Between Particles

III. Soil Characteristics D. Soil Cation Exchange Capacity

1. Remember: the ionic composition of the cloud is variable

A change in the ionic composition of the bulk solution will affect the cation species in the “cloud”

2. defined as the degree to which a soil can adsorb and exchange cations

Cations adsorb to the surface of the particular/organic matter (enter the cloud)


Adsorbed cations (minerals) are not easily lost Provide a nutrient reserve for plants

The net charge of the cloud doesn’t change (although the type of cation does change)

1 Ca2+ will replace 2 Na+

Dependent upon soil texture and organic matter content

The more clay, the more negative the soil, the greater the CEC


The more organic material, the more negative the particles, the greater the CEC

CEC is dynamic throughout a soil 3. CEC will increase with soil pH

Acidic soils will be high in H+ and Al3+

Neutral to moderately alkaline will be high in Ca2+ and Mg2+

Acid souls will be high in Na+


4. Available H+ ions will replace the cations and become available to plants

Plant root possess cation exchange capacity to remove the “reserve” nutrients

Soil Cation Exchange

III. Soil Characteristics E. Soil Porosity

1. Defined as the measurement of the open spaces between particles or pores

2. Porosity determines the total amount of water a soil or sediment will hold

3. Porosity is influenced by particle size, shape, and assortment

Sand soils have high porosity Clay and silt soils will have lower porosity

Silt fills the pore spaces

Pores and Porosity

III. Soil Characteristics F. Soil Permeability

1. The ability of soil to transmit water 2. Dependent upon the size of the pores and

their relative interconnectedness Sandy soil tend to be highly permeable

High porosity and highly connected Clay soil tend to be impermeable

High porosity but the pore spaces are tiny and have little interconnections

III. Soil Characteristics G. Soil Capillarity

1. Dependent on 3 water properties Adhesion, the ability of water to hold onto other

materials Cohesion, the ability of water to hold onto itself Surface tension, since water molecules are more

attracted to water than air, water surfaces behave like expandable films

III. Soil Characteristics G. Soil Capillarity

2. It is the upward movement of water though the pores

The adhesive force pulls the water upward through the soil

Pore size will limit the upward movement The larger the pore the lower the water can travel

Soil Capillarity

III. Soil Characteristics H. Soil Water-holding Capacity

1. Dependent on capillarity and pore size 2. The larger the pores the lower the water

holding capacity 3. Determines the amount of water available to

plants

Water-holding Capacity

IV. Soil Use and Abuse A. General Concepts

Actually measuring degradation is subjective Best measurement of degradation may be

biological productivity i.e. Crop yields

IV. Soil Use and Abuse B. Agricultural Land Degradation

Estimated crop-land losses each year are the size of the U.S. and Mexico

Approximately 11 million hectares/ 27 million acres

Does this make any sense????????????/ Some crop-land losses include

Urbanization Highway development

IV. Soil Use and Abuse B. Agricultural Land Degradation

Industrial sites Home developments Toxification from hazardous waste Chemical spills Salinization Pesticide overuse Erosion

IV. Soil Use and Abuse C. Erosion

Naturally redistributes organic matter and parent material nutrients

Can create landscapes like the Grand Canyon Water is a ‘natural force’ of erosion Excessive erosion occurs with a change in landscape

Earthquake Volcano Earth moving for human use

IV. Soil Use and Abuse C. Erosion

Overall erosion concern is with the loss of the topsoil

Fertilizer application will add nutrients lost to erosion

Total loss due to erosion is estimated to be 25 billion metric tons

Creates sediment loading issues in rivers and lakes

IV. Soil Use and Abuse D. Mechanism of Erosion

The two main agents of erosion are wind and water Sheet erosion is when uniform layers are peeled off

the land Rill erosion is when small channels are cut into soil by

water (mostly agriculture land) Gully erosion is enlarged rill, which form channels and

ravines. Streambank erosion is when soil is washed away

from the banks of streams and rivers Trees can eventually fall and are removed

IV. Soil Use and Abuse D. Mechanism of Erosion (cont)

Farms may lose up to 20 metric tons per hectare during winter and spring runoff

Only a few millimeters of soil, but more than replacement amount

With current farming techniques, the topsoil loss is much less

Ex: No till farming, cover crops

IV. Soil Use and Abuse E. Erosion in the US

May be the highest in the world (old estimates) 2.5 billion metric tons from crop lands 3.3 Billion metric tons from forests, pastures,

stream banks and construction

IV. Soil Use and Abuse• E. Erosion in the US (cont)

• Soil lost could fill 50 million box cars 500,000 trains with 100 cars

At the beginning of European settlement, topsoil had an average depth of 25 cm

Tremendous nutrient amounts

The U.S. has lost almost 1/2 of the topsoil from colonial times

Almost 2/3 of the soil carbon (makes soil black) Some areas no longer have topsoil

IV. Soil Use and Abuse E. Erosion in the US (cont)

Soil conservation Service was founded in 1935 Row crops expose topsoil Plowing overturns organic matter back into the soil,

but exposes mineral soil to erosion Herbicides kill plants that can hold soil in place

V. Soil Agriculture Resources A. Water

Water is necessary for plants 73% of water removed from lakes, streams, rivers is used for

Irrigation Water rich countries can irrigate more Farming practices which over irrigate the land is called water

logging and doesn’t work Accumulation of mineral salts, in certain soil types, can render

soil unusable. Called Salinization

Drip irrigation allows for plant needs to regulate irrigation flow

V. Soil Agriculture Resources B. Plant Nutrients from Soil

The primary soil solid nutrients are N,P,K The secondary soil solid nutrients are Ca, Mg, S Fertilizers add essential nutrients to the soil (mostly

primary soil solids) Soil micronutrients are just as important, usually needed

in very small amounts Some soil micronutrients are Fe, Mo, Cl, Co, Cu, Mn, B, and

Zn Carbon, Hydrogen, Oxygen are added through the air

(nitrogen is unusable)

V. Soil Agriculture Resources Alternate fertilizers are Manure, crop residues, ashes,

compost, “green” manure (plant residues, no food waste) Nitrogen is “fixed” by bacteria Fertilizers are energy expensive to make

C. Climate Changes in current climates could shift productivity of regions

of the glove to other regions Warming trends could move temperature needs northward

toward Canada( in the N. Hemisphere) Famine may be an issue in the future

V. Soil Agriculture Resources D. Energy

Farming is energy intensive Fossil fuels are used to provide needed energy

Farm machinery Fertilizer production Pesticide production Irrigation

VI. Sustainable Agriculture- also called regenerative farming

A. Newly Cultivated Land Japan is the most land poor country in the world

Only .06 hectares per person for food. Approximately 20m x 30m plot

Australia has the largest amount of land per person 2.1 hectares per person

The US is about one hectare per person Most improvements in agriculture are in terms of crop

varieties and land use Some countries are actually using less land than in previous

decades Mostly occurs in developing countries of South America and

Africa


B. Soil Conservation Managing topography

Water and erosion moves downhill Steeper the slope the greater the erosion rate Contour plowing, moves rows across the hill

instead of up and down Strip farming, planting different crops next to each

other along different strips. Harvesting occurs at different times, protecting the soil


Areas with high rainfall use tied ridges, cutting ridges at right angles to block water run off

Terracing, shaping of the land to create level shelves Edges have soil anchoring plants Allows farming of steep hillsides

Planting perennial species, areas with difficult settings allows for cultivation of those areas

Providing Ground Cover Leaving crop residues

Reduces soil erosion due to wind and rain Increases potential for disease over a long period of time Usually no more than 6 consecutive years

VI. Sustainable Agriculture- also called regenerative farming Cover Crops

Can be plowed under at harvest time to provide green manure

Ex: rye, alfalfa, clover, etc. Can be rolled over

Drill seed method Planting nutrient loaders

Provide nutrients for the soil Ex. Legumes, symbiosis provides nitrogen

Mulch, general ground cover, includes manure, wood chips, straw, seaweed, leaves, etc.


Some plants prefer high mulch areas

Low input sustainable Ag Use less inorganic fertilizers No pesticides Less water Less machinery Called “organic” farming

soil resources and sustainable agriculture soil is more than ‘dirt’ soil has 4 major components...

Documents

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