Soil Notes

General Soil Information

Soil Notes

Definition

Soil – relatively thin surface layer of the Earth’s crust consisting of mineral and organic matter that is affected by agents such as weather, wind, water, and organisms.

Composition – 4 Distinct Parts

Mineral particles (45% of “typical” soil)Organic matter (about 5%)Water (about 25%)Air (about 25%)

ImportanceOrganisms, mainly microorganisms, inhabit the soil & depend on it for shelter, food & water. Plants anchor themselves into the soil, and get their nutrients and water. Terrestrial plants could not survive without soil, therefore, humans could not exist without soil either.

SOIL: A RENEWABLE RESOURCESoil is a slowly renewed resource that provides most of the nutrients needed for plant growth and also helps purify water.

Soil formation begins when bedrock is broken down by physical, chemical and biological processes called weathering.

Mature soils, or soils that have developed over a long time are arranged in a series of horizontal layers called soil horizons.

Parent MaterialThe rock that has slowly broken down into smaller particles by biological, chemical, and physical weathering. To form 2.5 cm (1 in.) it may take from 200-1000 years.

Soil Formation

Physical Weathering

Ex. erosion (wind, water, ice, etc.)

Chemical Weathering

A plant’s roots or animal cells undergo cell respiration and the CO2 produced diffuses into soil, reacts with H2O & forms carbonic acid (H2CO3). This eats parts of the rock away.

Renewable or Not?

Decomposition produces new soil But, in the tropical rainforests, all of the nutrients are caught in the trees and when cut down & burned the soil cannot get the nutrients back.

TextureThe percentages (by weight) of different sized particles of sand, silt and clay that it contains.

Soil Properties:

Texture (Cont.)>2mm in diameter = gravel/stones (not actually considered soil because it doesn’t have direct value to plants.0.05 to 2mm = sand (the largest soil particles) can be seen easily with the eye.0.002 to 0.05mm = silt – about the size of flour and barely visible with the eye.<.002mm = clay (has the greatest surface value) – only seen under and electronic microscope.

Texture

To tell the difference in soil, take the soil, moisten it, and rub it between your fingers and thumb.

Gritty -has a lot of sandSticky- high clay content and you should

be able to roll it into a clump Silt- smooth, like flour.

Structure

How soil particles are organized and clumped together. (Sand, silt, clay)

Friability

How easily the soil can be crumbled.

Porosity

A measure of the volume of soil and the average distances between the spaces.

PermeabilityThe rate at which water and air moves from upper to lower soil layers. It is distances between those spaces.

Some Soil Properties

Soils vary in the size of the particles they contain, the amount of space between these particles, and how rapidly water flows through them.

Figure 3-25Figure 3-25

Fig. 3-25, p. 70

0.05–2 mmdiameter

High permeability Low permeability

WaterWater

Clayless than 0.002 mm

Diameter

Silt0.002–0.05 mm

diameter

Sand

Shrink-Swell Potential

Some soils, like clays, swell when H2O gets in them, then they dry and crack. This is bad for house foundations, etc.

pHThe pH of most soils ranges from 4.0 to 8.0. But, the soil of the Pygmy Forest in California is extremely acidic (2.8-3.9) and in Death Valley, California, it is very basic (10.5). Plants are affected by pH because of the solubility of nutrient minerals.

Slope

Steep slopes often have little or no soil on them because of gravity. Runoff from precipitation tends to erode the slope also. Moderate slopes and valleys may encourage the formation of deep soils.

Depth

Some soils are very shallow (like in some places in San Antonio). It can be only two inches of soil and then you hit rock. Other areas can have soil 36 inches deep or more.

Color

Dark soil is rich with lots of organic matter. Light soil (like sand) is not so rich with very little organic matter.

Soil Horizons

Organic Layer (O-horizon)

The uppermost layer; it is rich in organic material. Plant litter accumulates in the O-horizon and gradually decays. In desert soils the O-horizon is completely absent, but in certain organically rich soils it may be the dominant layer.

Topsoil (A-horizon)

It is dark and rich in accumulated organic matter and humus.It has a granular texture and is somewhat nutrient-poor due to the loss of many nutrient minerals to deeper layers and by leaching.

Subsoil (B-horizon)The light-colored subsoil beneath the A-horizon; it is often a zone of illuviation where nutrient minerals have leached out of the topsoil and litter accumulate. It is typically rich in iron and aluminum compounds and clay.

Parent Material (C-horizon)This contains weathered pieces of rock and borders the unweathered solid parent material. Most roots do not go down this deep and it is often saturated with groundwater.

Fig. 3-23, p. 68

Fern

Mature soil

Honey fungus

Root system

Oak tree

Bacteria

Lords and ladies

FungusActinomycetes

Nematode

PseudoscorpionMite

RegolithYoung soil

Immature soilBedrock

Rockfragments

Moss and lichen

Organic debrisbuilds upGrasses and

small shrubs

Mole

Dog violet

Woodsorrel

Earthworm Millipede

O horizonLeaf litter

A horizonTopsoil

B horizonSubsoil

C horizon

Parent material

Springtail

Red Earth Mite

Layers in Mature SoilsInfiltration: the downward movement of water through soil.Leaching: dissolving of minerals and organic matter in upper layers carrying them to lower layers.The soil type determines the degree of infiltration and leaching.

Fig. 3-24a, p. 69

Mosaic of closely packed pebbles, bouldersWeak humus-mineral mixture

Dry, brown to reddish-brown with variable accumulations of clay, calcium and carbonate, and soluble salts

Alkaline, dark, and rich in humusClay, calcium compounds

Desert Soil(hot, dry climate)

Grassland Soilsemiarid climate)

Fig. 3-24b, p. 69

Tropical Rain Forest Soil(humid, tropical climate)

Acidic light-colored humus

Iron and aluminum compounds mixed with clay

Fig. 3-24b, p. 69

Deciduous Forest Soil(humid, mild climate)

Forest litter leaf moldHumus-mineral mixtureLight, grayish-brown, silt loamDark brown firm clay

Fig. 3-24b, p. 69

Coniferous Forest Soil(humid, cold climate)

Light-colored and acidic

Acid litter and humus

Humus and iron and aluminum compounds

Case Study: Industrialized Food Production in the United States

Industrialized agriculture uses about 17% of all commercial energy in the U.S. and food travels an average 2,400 kilometers from farm to plate.


Fig. 13-7, p. 277

4%

Food production

Food distribution and preparation

Food processing

LivestockCrops5%6%2% 17%

of total U.S. commercial energy use

Traditional Agriculture: Low Input PolycultureMany farmers in developing countries use low-input agriculture to grow a variety of crops on each plot of land (interplanting) through:

Polyvarietal cultivation: planting several genetic varieties.Intercropping: two or more different crops grown at the same time in a plot.Agroforestry: crops and trees are grown together.Polyculture: different plants are planted together.

6.4 billion tons of soils are eroded from the U.S. each year; this would fill 320 million average-sized dump trucks that, if parked end-to-end, would extend to the moon and ¾ of the way back!

Erosion

Definition

Erosion is the movement of soil components, especially surface litter and topsoil, from one place to another.

Importance

In undisturbed ecosystems, the roots of plants help anchor the soil, and usually soil is not lost faster then it forms. But, farming, logging, construction, overgrazing by livestock, off-road vehicles, deliberate burning of vegetation etc. destroy plant cover and leave soil vulnerable to erosion. This destroys in a few decades what nature took hundreds to thousands of years to produce.

SOIL EROSION AND DEGRADATION

Soil erosion lowers soil fertility and can overload nearby bodies of water with eroded sediment.

Sheet erosion: surface water or wind peel off thin layers of soil.Rill erosion: fast-flowing little rivulets of surface water make small channels.Gully erosion: fast-flowing water join together to cut wider and deeper ditches or gullies.

SOIL EROSION AND DEGRADATION

Soil erosion is the movement of soil components, especially surface litter and topsoil, by wind or water.

Soil erosion increases through activities such as farming, logging, construction, overgrazing, and off-road vehicles.


Global Outlook: Soil Erosion

Soil is eroding faster than it is forming on more than one-third of the world’s cropland.


Case Study: Soil Erosion in the U.S. – Some Hopeful Signs

Soil erodes faster than it forms on most U.S. cropland, but since 1985, has been cut by about 40%.

1985 Food Security Act (Farm Act): farmers receive a subsidy for taking highly erodible land out of production and replanting it with soil saving plants for 10-15 years.

Water ErosionSplash – water hits the soil at a severe angle (based on slope)

This can erode soil.

Sheet – when surface water moves down a slope or across a field in a wide flow and peels

off fairly uniform sheets of soil.

Because the topsoil disappears evenly, sheet erosion may not be noticeable until too much

damage has been done.

Water Erosion (Cont.)Mass Slippage – (like in California) where it is very wet and large amounts of soil slip away in large chunks (mud slides).

Rill – concentrated flow across the surface of soil. Leaves rivets (micro channels).

Gully – rivulets of fast-flowing water join together and, with each succeeding rain, cut the channels wider and deeper until they become ditches or gullies. Gully erosion usually happens on steep slopes where all or most vegetation has been removed.

Wind Erosion

Saltation – one particle hitting another and being blown across the surface of the soil.

Suspension – airborne soil. Ex. soil from Lubbock is found in Temple, Texas.

Surface Creep – mountains/sand dunes; surface creeping slowly across. Landslides are an example of a very fast surface creep.

Desertification: Degrading Drylands

About one-third of the world’s land has lost some of its productivity because of drought and human activities that reduce or degrade topsoil.


Salinization and Waterlogging

Repeated irrigation can reduce crop yields by causing salt buildup in the soil and waterlogging of crop plants.


Fig. 13-13, p. 281

EvaporationTranspiration

EvaporationEvaporation

Waterlogging

Salinization Waterlogging1. Irrigation water contains small amounts of dissolved salts

2. Evaporation and transpiration leave salts behind.

3. Salt builds up in soil.

1. Precipitation and irrigation water percolate downward.

2. Water table rises.

Less permeable clay layer

Fig. 13-15, p. 281

CleanupPrevention

Soil Salinization

Solutions

Reduce irrigation

Switch to salt-tolerant crops (such as barley, cotton, sugarbeet)

Flush soil (expensive and wastes water)

Stop growing crops for 2–5 years

Install underground drainage systems (expensive)

Salinization and Waterlogging of Soils: A Downside of Irrigation

Example of high evaporation, poor drainage, and severe salinization.White alkaline salts have displaced cops.


Erosion Control (see Miller pg. 282)

Shelterbelts – can reduce wind erosion. Long rows of trees are planted to partially block the wind. They can also help retain soil moisture, supply some wood for fuel, and provide habitats for birds.

Minimum Tillage – (conservation tillage) to disturb the soil as little as possible while planting crops.

Special tillers break up and loosen the subsurface soil without turning over the topsoil, previous crop residues, and any cover vegetation.

SUSTAINABLE AGRICULTURE THROUGH SOIL CONSERVATION

Modern farm machinery can plant crops without disturbing soil (no-till and minimum tillage.

Conservation-tillage farming:• Increases crop yield.• Raises soil carbon content.• Lowers water use.• Lowers pesticides.• Uses less tractor fuel.

Contour Farming –sloping your growing crops, etc. You run terraces parallel to the ground to stop soil from running down a steep slope. Plowing and planting crops in rows across, rather than up and down, the sloped contour of the land.

Terracing – (what you use for contour farming.) Dirt goes up to hold the dirt in place. Broad, nearly level terraces that run across the land contour. Helps to retain water for crops at each level and reduce soil erosion by controlling runoff.


Terracing, contour planting, strip cropping, alley cropping, and windbreaks can reduce soil erosion.


Strip Cropping – a row crop such as corn alternates in strips with another crop that completely covers the soil, reducing erosion. It catches and reduces water runoff and helps prevent the spread of pests and plant diseases.

Cover Cropping (alley cropping) – several crops are planted together in strips or alleys between trees and shrubs that can provide shade (which reduces water loss by evaporation) and helps to retain and slowly release soil moisture.

Irrigation TechniquesConventional center-pivot irrigation- allows 80% of the water input to reach crops Gravity-flow irrigation- Valves that send water down irrigation ditches. Drip irrigation- Can raise water efficiency to 90-95% and reduce water use by 37-70%.Floodplain irrigation- allowing the natural floods to irrigate the crops. Soils in flood zones tend to be nutrient rich and fertile.

MacronutrientsMacronutrients are larger in atomic structure. Ex. Nitrogen, Phosphorus & Potassium.

MicronutrientsThese are smaller in atomic structure.

Plants need them in small amounts. Ex. Selenium, Zinc & Iron.

Soil Nutrients

Fertilizers and LabelsOrganic Fertilizers – animal manure, crop residues, bone meal, and compost

Inorganic Fertilizers – man-made from chemical compounds

Benefits – exact compositions are known; they are soluble & thus immediately available to the plant

Costs – quickly leach away; this pollutes the water; doesn’t help the water holding capacity of the soil like organic fertilizers do.

DefinitionHydroponics are growing plants in fertilized water.

Hydroponics:

Method of suspending plants in water and the solutions involved. Ex. cranberries are grown this way.

Costs of Hydroponics:

It is labor-intensive and expensive.

You can control the environment & grow plants where there is no soil; NASA is looking into this.

Benefits:


Fertilizers can help restore soil nutrients, but runoff of inorganic fertilizers can cause water pollution.

Organic fertilizers: from plant and animal (fresh, manure, or compost) materials.Commercial inorganic fertilizers: Active ingredients contain nitrogen, phosphorous, and potassium and other trace nutrients.

THE GREEN REVOLUTION AND ITS ENVIRONMENTAL IMPACT

Since 1950, high-input agriculture has produced more crops per unit of land.In 1967, fast growing dwarf varieties of rice and wheat were developed for tropics and subtropics.



Lack of water, high costs for small farmers, and physical limits to increasing crop yields hinder expansion of the green revolution.Since 1978 the amount of irrigated land per person has declined due to:

Depletion of underground water supplies.Inefficient irrigation methods.Salt build-up.Cost of irrigating crops.


Modern agriculture has a greater harmful environmental impact than any human activity.Loss of a variety of genetically different crop and livestock strains might limit raw material needed for future green and gene revolutions.

In the U.S., 97% of the food plant varieties available in the 1940 no longer exist in large quantities.

Fig. 13-18, p. 285

Biodiversity Loss Soil Water Air Pollution Human Health Loss and degradation of grasslands, forests, and wetlands

Erosion Water waste Greenhouse gas emissions from fossil fuel use

Nitrates in drinking water

Loss of fertility Aquifer depletionPesticide residues in drinking water, food, and air

Salinization Increased runoff and flooding from cleared land

Other air pollutants from fossil fuel use

Fish kills from pesticide runoff

WaterloggingSediment pollution from erosion Greenhouse gas

emissions of nitrous oxide from use of inorganic fertilizers

Contamination of drinking and swimming water with disease organisms from livestock wastes

Desertification

Killing wild predators to protect livestock

Fish kills from pesticide runoff

Surface and groundwater pollution from pesticides and fertilizers Belching of the

greenhouse gas methane by cattle

Loss of genetic diversity of wild crop strains replaced by monoculture strains

Bacterial contamination of meat

Overfertilization of lakes and rivers from runoff of fertilizers, livestock wastes, and food processing wastes Pollution from

pesticide sprays

THE GENE REVOLUTIONTo increase crop yields, we can mix the genes of similar types of organisms and mix the genes of different organisms.

Artificial selection has been used for centuries to develop genetically improved varieties of crops.Genetic engineering develops improved strains at an exponential pace compared to artificial selection.

Controversy has arisen over the use of genetically modified food (GMF).

Mixing GenesGenetic engineering involves splicing a gene from one species and transplanting the DNA into another species.


Fig. 13-19, p. 287

Projected DisadvantagesIrreversible and unpredictable genetic and ecological effects

Need less fertilizer

Need less water

More resistant to insects, disease, frost, and drought

Harmful toxins in food from possible plant cell mutations

Grow faster New allergens in food

Can grow in slightly salty soils

Lower nutrition

Less spoilageIncreased development of pesticide-resistant insects and plant diseases

Need less pesticides Can create herbicide-resistant weeds

Better flavor

Tolerate higher levels of herbicides

Can harm beneficial insects

Lower genetic diversityHigher yields

Trade-OffsGenetically Modified Crops and Foods

Projected Advantages

PRODUCING MORE MEATAbout half of the world’s meat is produced by livestock grazing on grass.The other half is produced under factory-like conditions (feedlots).

Densely packed livestock are fed grain or fish meal.

Eating more chicken and farm-raised fish and less beef and pork reduces harmful environmental impacts of meat production.

Fig. 13-21, p. 289

Trade-Offs

Animal Feedlots

Advantages Disadvantages

Increased meat production

Need large inputs of grain, fish meal, water, and fossil fuelsHigher profits

Concentrate animal wastes that can pollute water

Less land use

Reduced overgrazing

Reduced soil erosion

Antibiotics can increase genetic resistance to microbes in humans

Help protect biodiversity

How Many People can the World Support? Food Production and Population

The number of people the world can support depends mostly on their per capita consumption of grain and meat and how many children couples have.

Research has shown that those living very low on the food chain or very high on the food chain do not live as long as those that live somewhere in between.

PRODUCING MORE MEAT

Efficiency of converting grain into animal protein.


CATCHING AND RAISING MORE FISH AND SHELLFISH

After spectacular increases, the world’s total and per capita marine and freshwater fish and shellfish catches have leveled off.


CATCHING AND RAISING MORE FISH AND SHELLFISH

Government subsidies given to the fishing industry are a major cause of overfishing.

Global fishing industry spends about $25 billion per year more than its catch is worth.Without subsidies many fishing fleets would have to go out of business.Subsidies allow excess fishing with some keeping their jobs longer with making less money.

Aquaculture: Aquatic FeedlotsRaising large numbers of fish and shellfish in ponds and cages is world’s fastest growing type of food production.Fish farming involves cultivating fish in a controlled environment and harvesting them in captivity.Fish ranching involves holding anadromous species that live part of their lives in freshwater and part in saltwater.

Fish are held for the first few years, released, and then harvested when they return to spawn.

Fig. 13-24, p. 292

Trade-Offs

Aquaculture Advantages Disadvantages

High efficiency Needs large inputs of land, feed, and waterHigh yield in

small volume of water

Large waste output

Destroys mangrove forests and estuaries

Can reduce overharvesting of conventional fisheries Uses grain to feed

some speciesLow fuel use Dense populations

vulnerable to disease

Tanks too contaminated to use after about 5 years

High profits

Profits not tied to price of oil

Fig. 13-25, p. 293

Solutions

More Sustainable Aquaculture

• Use less fishmeal feed to reduce depletion of other fish

• Improve management of aquaculture wastes

• Reduce escape of aquaculture species into the wild

• Restrict location of fish farms to reduce loss of mangrove forests and estuaries

• Farm some aquaculture species in deeply submerged cages to protect them from wave action and predators and allow dilution of wastes into the ocean

• Certify sustainable forms of aquaculture

SOLUTIONS: MOVING TOWARD GLOBAL FOOD SECURITY

People in urban areas could save money by growing more of their food.

Urban gardens provide about 15% of the world’s food supply.

Up to 90% of the world’s food is wasted.


Solutions: Steps Toward More Sustainable Food Production

We can increase food security by slowing populations growth, sharply reducing poverty, and slowing environmental degradation of the world’s soils and croplands.

Technology

Soil Notes