Soil Characteristics, Degradation, and Conservation.

SoilCharacteristics, Degradation, and

Conservation

What is soil?

• Soil is derived from rock, and contains a large biotic component

– Supports plant life• What makes up soil

– 50% mineral matter– Up to 5% organic matter (living & dead microorganisms and

decaying material)– Rest is composed of water and air

• Soil itself can be defined as an ecosystem– Composed of living and nonliving components

How does soil form?

• Parent material– Base geological material in a particular location– Examples:

• Lava• Volcanic ash• Rock or sediment deposited by glaciers• Wind-blown dunes• Sediments deposited by rivers in lakes, oceans, etc.• Bedrock» Continuous mass of solid rock that makes up Earth’s crust

Processes responsible for soil formation…

• Weathering: the physical, chemical, and biological processes that break down rocks and minerals– First step of soil formation– Turns large particles into small particles

Physical Weathering Chemical Weathering

Biological Weathering

–Physical or mechanical weathering• Breaks down rocks without triggering a

chemical change in the parent material• Main forces: wind and rain• Varied by daily and seasonal temperature

variation– Causes the thermal expansion and contraction

of the parent material– Areas with extreme temperature fluctuations

have rapid rates of physical weathering» Water freezing and expanding in cracks – causes

physical weathering» Crystalline structure occurs in the water when it

freezes

– Chemical weathering• Occurs when water or other substances chemically interact

with the parent material• Warm, moist conditions usually accelerate the rate of

chemical weathering

– Biological weathering• Occurs when living things break down parent material by

physical or chemical processes– Ex. Lichens initiate primary succession by producing acid

» This acid chemically weathers the rock– Ex. Tree roots accelerate weathering as their roots grow and

rub against rock» Also accelerate chemical weathering through leaf

decomposition and chemical release from the roots into the soil

Role of erosion in soil formation…

• Erosion: the dislodging and movement of soil from one area to another – Deposits material it has depleted from another– Occurs when soil has no or little vegetation

• Surface is exposed to water and wind degradation

– Although it can sometimes help build new soil in the long term, on a human timescale erosion is

perceived as destructive

Role of biological activity in soil formation…

• Deposition, decomposition, and accumulation of organic matter– Deposition

• As living organisms die or deposit waste, the material is incorporated into the soil and mixes with minerals

– Ex: Trees drop their leaves → leaves decompose → detritivores and decomposers break down organic material → nutrients from leaves are added to the soil

– Decomposition• Complex organic molecules are broken down into smaller

ones• Partial decomposition of organic matter creates humus

–   dark, spongy, crumbly mass of material– Soils with humus hold moisture well and are good for plant growth

Decomposition Video: http://techalive.mtu.edu/meec/module10/Decomposition2.html

Soil Horizons• Horizon: distinct layer of soil

– Soil profile: cross section as a whole• From the surface to the bedrock

– Six major horizons• O Horizon – “litter layer”, consists of organic

material deposited by animals and plants• A Horizon – “topsoil”, consists of some organic material mixed with

mineral components• E Horizon – zone where minerals and organic material pass through

to mix in the topsoil• B Horizon – “subsoil”, where minerals and organic matter

accumulate• C Horizon – consists of weathered parent material unaltered or

slightly altered by soil formation• R Horizon – pure parent material

– Few soil profiles consist of all six horizons

Soil by Biome• Tropical Rainforest

– Very poor and infertile– Weathering has washed away most of the nutrients– Little organic matter because the warm temperatures encourage quick

decay

• Temperate Deciduous Forest– Very fertile– Replenished with falling leaves, twigs, and dead organisms– Cool enough temperatures allow slow decay

• Grassland– Nutrient rich

• large amount of plant material added daily– Contains large portions of clay, that retains water in the soil for later use

by plants– Often converted into farmland

• Desert– Little or no chemical weathering– Erosion, frost, sedimentation, and temperature fluctuations break

down the rocky soil into sand– Clay particles, since the silt and sand particles are easily blown

away

• Taiga– Acidic soil due to needle-like “leaves”– Top layer is covered with rocks

• Makes it hard for nutrients to reach the soil• Plants are unable to grow between the rocks without difficulty

• Tundra– Lack of nutrients due to short growth period during the summer– Permafrost: frozen deep layers of soil– Hard for plants to survive the harsh winters

Importance of topsoil for agriculture and ecosystems

• Consists of mostly inorganic mineral components– Ex: Weathered substrate

• Benefit for plants– Most nutrient-rich horizon– Loose texture– Dark coloration– Strong water-holding capabilities

• Due to humus

• Vital for agriculture– Agriculture can deplete the organic matter in the topsoil,

reducing the soil’s fertility and ability to hold water

The Leaching Process

• Leaching: process where solid particles suspended or dissolved in a liquid are transported to another location– Ex: Nutrients in soil– Similar effect of a coffee filter

• When it rains, water enters the soil, dissolves some of its components, and carries them downward into the lower horizons

Soil Characteristics

• Scientists classify soils by…– Color– Texture– Structure– pH

• These characteristics affect soil’s ability to provide plants with nutrients

Color

• Indicates the composition and fertility– Black and brown: rich in organic matter – Pale gray and white: leaching or low organic

content• Farmers used to rely

on the color of topsoil

to determine the area’s

potential to support

crops and livestock

Texture

• Determined by the size of particles• The United States Department of

Agriculture (USDA) uses 3 categories of soil– Clay: particles less that 0.002 mm in diameter– Silt: particles 0.002-0.05 mm in diameter– Sand: particles 0.05-2 mm in diameter– Loam: mixture of all three soil particles

• Soil texture influences a soil’s “workability”• Soil porosity: a measure of the size of

spaces between particles– The finer the particles, the smaller the spaces

between them• Harder for water and air to move throughout the soil• Slows infiltration and reduces the amount of oxygen

available to organisms in the soil

– Large soil particles allow water to pass through quickly• Roots unable to take in water• Require frequent irrigation

• Silty and loam soils are the best for plant growth

Structure• Measure of the “clumpiness” of soil• Encourages soil productivity• Soil clumps that are too large discourage

plant roots from growing• Plowpan: a hard layer of soil that resists

water transportation and root penetration, due to farmers repeatedly plowing the same field at the same depth– Repeated tilling can compact soil

• makes it less able to absorb water

pH

• pH: the degree of acidity or alkalinity• Influences a soil’s ability to support plants

– Plants usually die in soils that have extremely acidic or alkaline pHs

– Moderate variation influences the availability of nutrients for plants

Cation Exchange

• Cation: positively charged ion– Held in soil particle surfaces that are negatively

charged• Ex: Calcium, magnesium, potassium

• Cation exchange: process

through which plants gain

nutrients1. Plant roots donate hydrogen

ions to the soil in exchange

for cations

2. Soil particles then replenish with

exchange with water in the soil

• Cation exchange capacity: a soil’s ability to hold cations– Prevents them from leaching– Makes them available to plants– Useful measure of soil fertility– Soils with fine texture and rich in organic

matter have the highest• As soil pH decreases (more acidic), cation

exchange capacity diminishes– Nutrients leach away – soil then may supply

plants with harmful aluminum ions– Why acid rain harms plants

Soil and Its Relationship to Agriculture

Irrigation is the controlled application of water for agricultural purposes through manmade systems to supply water requirements not satisfied by rainfall.

Irrigation Methods• Center pivot-This is a form of overhead

irrigation. Steel or aluminum pipes are joined together, supported by trusses, mounted on wheeled towers. The sprinklers are situated on the length of the tower and they move in a circular motion.

• Drip-A planned irrigation system in which water is applied directly to the Root Zone of plants by means of applicators (orifices, emitters, porous tubing, perforated pipe, etc.) operated under low pressure with the applicators being placed either on or below the surface of the ground.

• Flood-The application of irrigation water where the entire surface of the soil is covered by ponded water.

• Furrow-A partial surface flooding method of irrigation normally used with clean-tilled crops where water is applied in furrows or rows of sufficient capacity to contain the designed irrigation system.

• Gravity-Irrigation in which the water is not pumped but flows and is distributed by gravity.

• Rotation-A system by which irrigators receive an allotted quantity of water, not a continuous rate, but at stated intervals.

• Sprinkler-A planned irrigation system in which water is applied by means of perforated pipes or nozzles operated under pressure so as to form a spray pattern.

• Sub-irrigation-Applying irrigation water below the ground surface either by raising the water table within or near the root zone or by using a buried perforated or porous pipe system that discharges directly into the root zone.

• Traveling gun-Sprinkler irrigation system consisting of a single large nozzle that rotates and is self-propelled. The name refers to the fact that the base is on wheels and can be moved by the irrigator or affixed to a guide wire.

• Supplemental-Irrigation to ensure increased crop production in areas where rainfall normally supplies most of the moisture needed.

• Surface-Irrigation where the soil surface is used as a conduit, as in furrow and border irrigation as opposed to sprinkler irrigation or sub-irrigation.

Problems Due to Irrigation• Water-logging- the irrigation

water eventually raises the water table in the ground -- the upper level of the groundwater -- from beneath.

• Salinization-occurs in warm and dry locations where soluble salts precipitate from water and accumulate in the soil.

• Leaching-The removal of soluble material from a soil or rock, through the percolation of water.

Solutions/Preventions of irrigation problems:

• Use soil moisture detectors so that the crops are only watered when it is needed

• Use time controlled valves on gravity flow systems

• Use water that is low in salinity

• Only use the amount of water needed to grow the plant, no extra

Soil Degradation

• Population and consumption increase– As the population of humans increase, so does the

consumption and call for goods. More crops must be grown which can hurt the soil.

• Erosion can degrade ecosystems– Erosion can ruin the soil and prevent plants from

growing. Without the proper producers in an ecosystem, then there can be no other organisms either.

• Soil erodes by several mechanisms

sheet-Detachment of soil particles by raindrop impact and their removal down slope by water flowing overland as a sheet

rill-An erosion process in which numerous small channels, typically a few inches deep, are formed. It occurs mainly on recently cultivated soils or on recent cuts and fills.

gully-Water flows in narrow channels during or immediately after heavy rains or melting snow.

• Conventional tillage-Full width tillage which disturbs all of the soil surface and is performed prior to and/or during planting. – Tillage is the agricultural preparation of the soil by ploughing, ripping, or turning

it.

• Soil erosion is a global problem– Erosion is a process that removes soil layers and carries

them away from farmer's fields to bodies of water or other land. Erosion results in the loss of valuable soil and its nutrients that are necessary for crops to grow. There are three primary kinds of erosion: wind, water, and tillage. In areas where the land is especially flat or dry, wind erosion is a problem.

– Soil erosion results in the loss of soil fertility and makes the land barren. There are more than 25 million hectares of barren lands in the world now.

Desertification reduces productivity of arid lands

• Deterioration in soil and plant cover have adversely affected nearly 50 percent of the land areas as the result of human mismanagement of cultivated and range lands.

• Overgrazing and woodcutting are responsible for most of the desertification of rangelands, cultivation practices inducing accelerated water and wind erosion are most responsible in the rain-fed croplands, and improper water management leading to salinization is the cause of the deterioration of irrigated lands.

• Between 1879 and 1929 the cultivation of land in the states of Oklahoma, Texas, Kansas, New Mexico, and Colorado soared.

• Farmers grew abundant wheat and ranchers grazed thousands of cattle

• Both types of agriculture contributed to erosion by removing native grasses and breaking down soil structure.

The Dust Bowl

• In the early 1930s, a drought occurred in the region. • Strong winds began to erode millions of tons of top soil.• The winds carried the dust over a thousand miles,

blackening rain and snow in New York and Vermont.• The most affected region in the southern Great Plains

became known as the Dust Bowl.• The “black blizzards” of the Dust Bowl forced thousands

of farmers off their land

Works Cited• http://ga.water.usgs.gov/edu/irquicklook.html

• Old textbook & new textbook

The Soil Conservation Service

Objective: To slow soil degradation.

The Soil Conservation Service

• In response to the devastation in the Dust Bowl the U.S. Congress passed the Soil Conservation Act of 1935, which established the Soil Conservation Service (SCS).

The Soil Conservation Service

• The SCS worked directly with farmers to develop conservation plans for individual farms which followed several aims and principles:– Assessing the land’s resources, problems, and

opportunities.– Prepare an integrated plan for each property.– Ensure that conservation plans correspond with

users’ objectives. – Implement conservation measures on individual

properties to contribute to the overall quality of life.

The Soil Conservation Service

• SCS promoted soil-conservation practices through county-based conservation districts. These districts:– Operate with federal direction, authorization,

and funding.– Implement local soil conservation programs,

in hopes of getting residents to plan ahead.

The Soil Conservation Service

• In 1994 the SCS expanded to include water quality protection and pollution control.

• It was renamed the Natural Resources Conservation Service.

• The SCS inspired similar efforts around the world.

How farmers can protect against soil degradation:

Crop Rotation• The practice of growing various crops on

the same piece of land in a planned sequence.

• An example of a common sequence would be a rotation between high and low residue crops – i.e. wheat and

soybeans.

Contour Farming

• The use of plowing to form ridges which change the direction of run-off so that it can settle into the soil and prevent soil erosion.

Terracing

• The creation of “steps” on a hillside so water can be contained.

• The end result looks like a staircase.

Rice terracing

Intercropping• The cultivation of two or more crops in the

same area.– Increases plant biodiversity to help disguise

plants from insect species.– Increases the density to suppress weed

growth.– Improves the overall

health of crops and decreases chance of disease.

Strip Cropping

• The practice of growing planned rotations of row crops, forages, small grains, or fallow in a systematic arrangement of equal width strips across a field.

Alley cropping

• A type of intercropping that involves arranging crops in alternate rows.

Agroforestry

• An approach of combining trees and shrubs with crops and/or livestock to produce a more diverse, productive, profitable, healthy and sustainable land-use.

Shelterbelt

• A plantation usually made up of trees and shrubs to protect against wind and prevent soil erosion.

Tillage• The agricultural preparation of soil by

ploughing, ripping, or turning it.• Different levels of tillage:

– Intensive: leaves 15% or less of crop residue in the soil

– Reduced: leaves 15%-30% of crop residue in the soil.

– Conservation: Leaves a minimum of 30% of crop residue in the soil.

• Many different acts were passed to promote, protect, and restore soil conservation.

• These acts were passed in the late 20th century. • They were both in the US and some were

international.

The Food Security Act of 1985

• Goes for the conservation of wetland, wildlife and quality of water

• This is promoted in order to conserve wetlands on agricultural lands.

• Required farmers to adopt soil conservation plans and practices as a prerequisite for receiving price support and other government benefits.

Conservation Reserve Program

• 1985• Voluntary program • Provides farmers with an opportunity to receive

money for taking highly erodible land out of production and using water and soil conservation acts with it.

• Protects topsoil from erosion • Protects a lot of natural resources• Protects many lakes, rives, stream, and oceans

Federal Agricultural Improvement and Reform Act

• “Freedom to Farm Act”• 1996• Revises and simplifies direct payment programs

for crops and eliminates milk price supports throughout the direct government purchases.

• It also reduces subsidies and government influence over many farm products.

• Led to many other acts to promote and pay for the adoption of conservation practices in agriculture.

Environmental Quality Incentive Program

• 1996• This is mainly for farmers and ranchers who are

facing threats with their soil, water and natural resources.

• Provides a conservation program for farmers and ranchers that would like to promote agricultural production and environmental quality as a compatible national goal.

• It offers financial and technical help to manage these practices on eligible agricultural land.

Natural Resource Conservation Foundation

• Part of the 1996 Farm Bill• Wanted to promote and fund innovative

solutions to conservation problems through effective partnerships.

• Wanted to conserve agricultural land. • Promoted partnerships between private

land owners and government

Works Cited• http://www.fsa.usda.gov/FSA/webapp?area=home&subject=copr&topic=crp • http://www.fns.usda.gov/snap/rules/Legislation/history/PL_99-198.htm • http://www.nrcs.usda.gov/PROGRAMS/EQIP/index.html#intro• http://www.tpwd.state.tx.us/landwater/land/private/farmbill/eqip/• http://uscode.house.gov/download/pls/16C78.txt• Textbook