Link to:  Carbon Farming Initiative,  Australian Government

<http://www.cleanenergyregulator.gov.au/Carbon-Farming-Initiative>

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Carbon Emissions from Urban Sprawl

Ted Floyd
Jan 2012

Carbon emissions, Urban sprawl, Land use, Land form, Green urbanism, Eco-city, Population density, Urban design, Climate change

Soils are a source of greenhouse gases when surface vegetation is destroyed and soil organic matter decomposes into carbon dioxide. When new houses are constructed, surface vegetation is destroyed and soil organic matter decays into the greenhouse gas, carbon dioxide.

Surface soils are sealed by houses, driveways, paths, paving, swimming pools, sheds, roads and concrete/asphalt footpaths. Plants do not grow in sealed soils and plants do not synthesise organic matter from atmospheric carbon dioxide during photosynthesis. There is no plants to add organic matter to sealed soils.

Vigorous plant growth in a garden will help to store carbon in soils.

In this report calculations are made of carbon dioxide emissions from vegetation and soil organic matter during house construction. A typical house block and surroundings releases 12,000 kg of carbon when virgin forests are cleared for housing in the Sydney region. (see appendix for calculation)

Many variables exist in new housing developments and this report uses typical values of carbon content of forests and soils in Australian ecosystems. (1) The size of new house blocks is decreasing in Sydney and the size of new houses is increasing. The size of new house blocks have decreased from 800 sq m in 1993 to 750 sq m in 2003. Many new freestanding houses are now 2 stories and back yard gardens are very small.

Sealed soils
When buildings and roads cover the soil surface plants cannot grow and the surface soil is sealed.

Impervious soils do not allow rain water to enter the surface soil and penetrate deep into the subsurface. Drainage engineers measure the extent of impervious soils when calculating the surface runoff.

Area of sealed soils preventing plant growth are generally the same as the area of impervious spoils. Plant growth does not occur when soils are impervious with no water infiltration.

An estimation of the carbon dioxide released into the atmosphere from the land when building a house is calculated by multiplying the carbon in vegetation and soil by the affected area of land.

Dead plants are not all converted immediately into carbon dioxide after the land is cleared. If dead plants are burnt, carbon dioxide is immediately released into the atmosphere. Dead plants will slowly decompose into carbon dioxide with the aid of microorganisms. Some wood may be used to make furniture and other long lasting products. In this report it is assumed all of the vegetation is burnt or decomposes into carbon dioxide.

Soil organic matter will slowly decompose into carbon dioxide. If the soil is anaerobic, methane is produced. Methane is a more powerful greenhouse gas than carbon dioxide. Parts of the soil organic matter will be resistant to decomposition and humus could remain in soils for many years and even hundreds of years. In this report it is assumed all soil organic matter decomposes into carbon dioxide.

Carbon emissions are calculated from after the clearing of virgin forest. Many housing developments are on agricultural land where the forest was cleared many years ago and a high portion of the carbon emissions occurred many years ago. Emissions are lower in areas of lower rainfall and poorer soils where growth of virgin forest is lower.

Roads
Road surfaces sealed by tar and concrete contributes a significant amount carbon dioxide to atmosphere from soils. Area sealed by streets and footpaths can equal 1/3 of total area of residential suburbs. (2)

Generally the surface area of streets increase when house blocks are larger. In many new developments streets are narow and curving with many cul-de-sacs producing denser developments with more house blocks per hectare and less road surface per house. Simple economic forces generate more house blocks and less roads per hectare.

Recent developments have a higher density and a smaller area of roads and this is a positive factor reducing carbon emissions. Provision of public transport often rsults in less land uptake than roads and expressways. Parking spaces also seals soils.

Urban sprawl
High densities and high rise developments will reduce the land uptake by an expanding population.

High density urban developments have a number of factors helping to reduce energy use and pollution from transport. Trip length is reduced and public transport is more viable. It is easy to walk to shops and public transport.

On individual house blocks, the area of soil sealed will depend on size of driveways, extent of concrete paths and paving and swimming pools.

In water sensitive urban design many techniques are used to reduce surface water runoff by increasing the area of permeable soils. Often the increase of permeable soils will be a positive factor reducing the extent of sealed soils and carbon emissions.

Greenhouse gas emissions
The emission of 12,000 kg of carbon during land clearing for new houses is significant.
In comparison an average house emits each year 2,000 kg carbon. The one-off emission of 12,000 kg is equivalent to 6 years of emissions from households.

The extent of land uptake and the clearing of vegetation should be taken into account for different types of developments. Higher density housing estates will result in lower carbon per head of population. Construction of units several stories high reduces land uptake and carbon emissions per resident.

Urban sprawl contributes to many environmental problems. The clearing of vegetation and the formation of sealed soils contributes to greenhouse gas emissions. Urban sprawl is a symptom of poor planning in the inner suburbs. The population of the inner suburbs should increase so as to reduce pressures on the growth of urban sprawl.

References

(1) National Greenhouse Gas Inventory 1988 and 1990, Australian Government 1994.

(2) Port Jackson South Stormwater Management Plan. EPA, NSW 1999.

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Carbon Storage in Parks and Gardens
Revision September 2011

by Ted Floyd

Carbon Gardens, Carbon Farming, Soil Carbon Sinks, Soil Organic Matter

Is it time to encourage the creation of soil carbon sinks?

Carbon Farming
Adding organic matter to farm soils and creating carbon sinks will improve soil fertility, reduce erosion and establishes drought tolerance. These soil qualities improve farm productivity, reduce costs and increases farm income.

Wheat production using minimum tillage or establishing deep rooting perennial grasses for sheep and cattle production are two well known ways of increasing soil organic matter.

The Australian Government introduced legislation for a carbon tax in 2011 and included a Carbon Farming Initiative designed to provide incentives for Carbon Farmers to create soil carbon sinks. (1)

Carbon Gardens
Soil carbon sinks can be established in the suburbs of our towns and cities. Native bush with large trees and an extensive understory will store carbon above and below ground level. Very little original bush remains in old Sydney suburbs and now bush regeneration enthusiasts and councils are planting native vegetation in parks and gardens.

A very dense vigorous forest can store 261 tonnes of carbon per hectare. (2) A wetland may store 300 or more tonnes of Carbon per hectare.

Irrigation of tree-lined valleys
Irrigation will increase plant growth and carbon storage. In urban areas excess water runoff during heavy rain can be harvested for irrigating planted bush areas. Trees planted on the lower slopes of valleys, beside creeks, can be irrigated with stormwater runoff from drains flowing into the creek.

In Whites Creek Valley local residents and Leichhardt Council are planting native vegetation to form a green corridor along the valley. There is the potential in suitable areas in this valley to
harvest stormwater and irrigate native trees.

Irrigation in a tree-lined valley will increase carbon storage and reduce flooding and pollution from stormwater runoff. Biodiversity will increase when there is vigorous plant growth. Soils beside creeks on the valley floor is often fertile and supports vigorous plant growth. Soils further up the slopes of a valley are usually shallower and less fertile. Soils on floodplains are often very deep and fertile. In the Sydney region when deep valleys occur with steep slopes a gully rainforest will grow.

At least 2 to 3 times more carbon is stored in wetlands than in trees. Whites Creek Wetland is a new, artificial wetland. Plant growth in this wetland is vigorous and continual maintenance is required to remove excess vegetation.

Growing a carbon sink
Carbon can be stored in home gardens. Native species, especially native trees will help create carbon sinks in the back yard. Drought tolerant species should be chosen. Carbon gardens can be created in flower and vegetable gardens. (3)

Composts, mulches, manures and suitable organic fertilizers increase soil organic matter. Digging soils and leaving soil surfaces bare will reduce organic matter.

Deep roots encourage the growth of carbon sinks. Native gum trees often have very deep roots, up to 40 meters, while fruit trees only 0.6 to 1.3 meters. Lawn grasses have very shallow roots, Poa annua only 0.15 m and Kikuyu deeper up to 2.4 m.

Generally carbon sinks do not form under impermeable surfaces. Plants seldom grow under houses and paving. Large trees sometimes have roots growing under houses and footpaths. Kikuyu will grow under footpaths. To form carbon sinks it is best to reduce the area of paving and to encourage plant growth over most of the backyard.

All plant material collected while gardening should be returned to the soil. We do not need council garbage trucks laden with dead garden waste heading to the rubbish dump emitting tonnes of carbon dioxide.

Water runoff collected from the roves of houses should be directed onto garden soils. After rainwater tanks are filled up and overflowing, excess water can be directed onto the top of raised garden terraces where water is stored during rain periods. Over the following days, water will gradually seep from the top terraces down through the soil to lower levels in the garden. Gardeners should aim to prevent any water flowing into council gutters.

Addition of organic matter to soils improves infiltration and water storage. This improves drought tolerance in gardens.

Hungary little microbes eat fallen leaf litter allowing plant nutrients to become available to growing plants. Small soil animals distribute nutrients by eating, moving around and depositing body wastes deep in the soil. Healthy soils are teaming with bacteria, fungi, actinomycetes
and tiny critters, all eating fallen leaf litter and eating each other.

A small gum tree in a backyard garden may store 1 tonne of Carbon with 1/2 above ground and 1/2 in the soil. (4)

With careful management of a garden, containing several trees, it should be possible to store 4 tonnes of Carbon in a 4m x 25m garden with equal amounts of Carbon above ground and in the soil. The average home emits about 2 tonnes of carbon a year.

In a typical house two years emissions from the house can be stored in the garden. These calculations indicate it would be difficult for a home garden to store all emissions from a house in the backyard garden. A carbon neautral house could be formed by an enthusiastic greenthumb living in a solar house.

Many people enjoy pottering in the garden, it is often a time of reflexion and helps to cope with the stress of modern living. While in the backyard garden people are not burning up fossil fuels watching TV and the exercise will help to prevent nasty health problems.

Modern global economies encourages growth and an increase in standard of living. Would it be better to aim for a better quality of life?

The storage of carbon in soils should be encouraged. Large quantities of carbon can be stored in urban soils and research and education programs should aim to encourage councils and home gardeners to increase the organic matter of soils in parks and gardens.

Appendix
Encouraging the growth of plants in urban soils has many advantages. Flooding is reduced [Transpiration Benefits For Urban Catchment Management], and [Urban Catchments Enhanced By Green Corridors]. Air Temperatures are reduced in urban areas by plants [Cool Trees] and urban creeks [Rehabilitation Of Urban Creeks] will create cool spaces in the suburbs.

Many soil scientists warn we are rapidly losing good agricultural land [Peak Soil]. Growing food in the suburbs can help to secure food supplies in cities.

Natural carbon cycle
Carbon dioxide in the atmosphere is converted into plant material during photosynthesis. Organic carbon compounds from plants are added to the soil and eaten by microbes and animals. During respiration animals and microbes breath out carbon dioxide into the atmosphere. [Carbon Cycle in Soils]

The natural carbon cycle is essentially a closed loop with no carbon added or subtracted from ecosystems. Small changes do occasionally occur.

Burning fossil fuels adds carbon dioxide to the atmosphere.
Clearing native forests and the decomposition of plant material adds carbon dioxide to the atmosphere.

A carbon sink can be created in soils by adding organic matter to soils. Growing plants can help create a carbon sink. Composts and mulches can help create a carbon sink. A carbon sink is only created when organic matter is added faster than the rate of decomposition of organic matter by animals and microbes.[Soil Organic Matter]

Lignin and cellulose decompose slowly and form long lasting soil humus. Sugars and carbohydrates decompose quickly and disappear from soils.

In the creation of carbon sinks it is often claimed long lasting compounds like humus must be formed. Humus is beneficial. Easily decomposed compounds similar to sugars and carbohydrates should also be able to form carbon sinks when the rate of adding these compounds to the soil is faster than the rate of decomposition.

When long lasting humus is formed it is considered the carbon sink is secure for hundreds of years. For rapidly decomposing compounds the carbon sink is only temporally and will disappear if soil management changes or the plants are removed.

Biochar is a carbon compound similar to charcoal. It is made by a process called pyrolysis when organic matter is heated to high temperatures in the absence of air. The primary aim of pyrolysis is to manufacture` an alternate energy source and the solid waste is biochar. A lot of research is now carried out on biochar throughout the world and small plants are operating. (5)

Biochar is resistant to breakdown in soils and it is expected it will form long lasting soil carbon sinks. There is many questions concerning large scale manufacture of biochar. Often biochar proposals will use plant material which should be left on the ground. Cutting down forests for a pyrolysis plant is not the best way to go. Small farm size plants may have advantages. Remember biochar is a waste product looking for a use.

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Water and Carbon in Garden Soils

Carbon Cycle in Soils
Photosynthesis in green leaves CO2 in air synthesised into sugars
Sugars transported in stems to all parts of plant
Exudates from roots deposited in soil and becomes food for microorganisms
Plants eaten by animals and respiration produces energy and CO2 returned to atmosphere
Leaf litter forms from dead leaves, bark and stems
Soil organic matter
Microrganisms
CO2 is released during respiration by insects and microorganisms and
Inorganic plant nutrients are released into the soil in a soluble form available to plants.
WATER and CARBON in GARDEN SOILS
Vigorous plant growth, irrigated by water harvesting will establish carbon sinks in urban gardens.

Water cycle
Water harvesting: Water collected from the roof of a house and used to irrigate the home garden. Water can be stored in a water tank and used in dry times or water from the roof spread directly on the garden during rain periods.

When raindrops come to earth they are absorbed by the soil or if there is too many of them they will flow down hill over the soil surface.

Transpiration is the movement of water from soils up the roots and stems of plants and into atmosphere. Water movement up roots and stems is essential to carry plant nutrients from soils to the growing parts of the plant.

Excess rainfall is not absorbed by soils and flows downhill over the land surface into drains and creeks. Flooding is reduced when more water is absorbed by soils and less water allowed to enter drains.

Water harvesting reduces downstream flooding and reduces severity of droughts in gardens. Organic matter improves water penetration into soils and increases water storage in soils.

Irrigation increases plant growth. The use of town water may not be available in the future and to ensure good plant growth in urban gardens water harvesting is necessary. Water tanks are very useful and storage of water in soils will help plants to grow in dry times.

Water collected on the roof of a house and spread over a garden area of equal size to the house, doubles the total rainfall. For this to work the soil has to be well prepared. The ground surface needs to be very permeable to allow water to soak down into the earth.

IMPROVING WATER INFILTRATION INTO GARDEN SOILS
Increase plant cover to protect soil surface
Encourage plants with deep roots
Improve soil structure
Add mulches, green manures and compost
Encourage earth worms
Add soil improvers such as gypsum
Maintain rough soil surface
Protect the soil from raindrop impact
Reduce soil compaction
Improve subsurface drainage
Use organic fertilizers and animal manures
Growing plants encourages water to penetrate deep into soils. A variety of plants with different root systems will allow water stored in the soil at different depths to be utilized.

Carbon sinks
Carbon dioxide in the atmosphere causes greenhouse effect and air temperatres to rise. A carbon sink is created when carbon is removed from the atmosphere and locked up in a form away from the atmosphere and not causing a rise in air temperature.

Photosynthesis: In green chlorophyll of plant leaves, organic compounds are synthesised using energy from sunlight, water from soils and atmospheric carbon dioxide CO2.

Photosynthesis is the basic process producing food and energy by plants. Animals eat plants and each other and there food and energy is originally synthesised by photosynthesis.

Respiration:Plants and animals use oxygen from atmosphere and living compounds to produce energy and exhale carbon dioxide CO2 to atmosphere. All living organisms respire including plants, animals and microorganisms.

In a mature native forest the rate of photosynthesis is nearly equal to the rate of respiration. There is a balance and no CO2 is added or subtracted from the atmosphere. If the forest is cut down photosynthesis in trees stops and respiration by soil microorganisms continues and extra CO2 is added to the atmosphere increasing the greenhouse effect. If trees are planted and nurtured in cleared land and photosynthesis is faster than respiration a carbon sink will form.

Carbon sinks can be formed from any plants growing at a faster rate than total respiration. In most farming land respiration is faster than photosynthesis so CO2 is added to the atmosphere.

Carbon sinks in urban gardens are created by living plants growing above and below the ground surface. Green plants absorb carbon dioxide from the air and manufacture plant material by photosynthesis in leaves.

Below ground level, organic matter in soils is a very important carbon sink. Leaves and stems fall onto the soil surface, forming a leaf litter. Many small animals and microorganisms break down large dead plant remains into small pieces, incorporating broken down plants into soil organic matter.

Benefits of soil organic matter
Food for microorganisms and soil animals
Nutrient cycling
Store plant nutrients in soils
Reduce harmful changes in soil acidity and alkalinity
Improve soil structure
Improve soil aeration
Reduce erosion
Increase water infiltration
Improve water holding capacity
Create healthy soils and encourage vigorous plant growth
Are a very good carbon sink and reduce greenhouse gases
Organic matter in soils is found in varying stages of decay. On the soil surface plant residues occurs including leaf litter and mulches. Particulate organic carbon is small plant remains, humus is very small particles synthesized by microorganisms. Charcoal is mainly carbon and is resistant to decay, lasting for hundreds of years.

Plants are made from sugars, starches, cellulose, fats, oils, proteins and lignin. Sugars are very quickly eaten by microorganisms, cellulose is slowly converted to sugars and lignin is very resistant to decay and may survive in soils for hundreds of years. Organic matter is mainly dead, decomposing plant material. Only a small proportion originates from animals. Animal bones, CaCO3 is a inorganic compound containing carbon.

The amount of carbon is often equal above and below ground level. Carbon in soils increases in cold or wet conditions. Woody plants, containing lignin, forms humus resistant to microbial breakdown and will persist in soils for hundreds of years.

Carbon sinks will be bigger when there is extra plant growth in soils with desirable physical properties.

The build up of soil organic matter by returning garden cuttings, compost and mulches to soils will add nutrients to the soil. The addition of organic materials to soils will improve soil physical properties. Structure is stable, improving soil aeration and water movement. Water holding capacity is increased, improving drought tolerance. Damage from erosion and the beating action of raindrops is decreased.

Cultivation and digging soils can reduce soil organic matter. Digging soils increases aeration and this can increase the decay of organic matter. Cultivation kills plants and this can reduce the build up of organic matter.

Hardwood trees and shrubs and especially gum trees form long lasting humus in soils.

Well managed garden soils will contain up to 10% organic matter. A small gum tree can store up to 1 tonne of carbon with ½ half above ground and ½ half in the soil. It is possible to store 4 tonnes of carbon in 100 square meters of garden containing several trees.

During a hot summers day trees will cool a backyard garden and strategically positioned plants will cool a house. Tall trees provide welcoming shade and growing plants transpire water from their leaves into the air producing a cooling effect.

Above article is an extract from report 1st published on Ramin webpage
www.ramin.com.au/creekcare/water-and-carbon-in-soils.shtml © Ted Floyd 2010. Last updated 22 February 2010. Webdesign © 2010 ramin communications.

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CARBON SINKS

In Urban Soils and Backyard Gardens

Ted Floyd

Oct 2009

Carbon storage in backyard gardens will help to cool the greenhouse.

Soil carbon sinks can be established in the suburbs of our towns and cities. Backyard gardeners can increase the amount of organic matter in the soil by carefully nurturing the soil.

Soil organic matter is the decaying remains of plants and animals and consists of carbon compounds.

Organic matter is important in forming healthy fertile soils. Plant nutrition and soil physical properties are improved in soils containing an adequate supply of organic matter.

Soils are a very good carbon sink and have the potential to reduce the adverse effects of global warming. Carbon dioxide is released into the atmosphere from decomposing organic matter and is absorbed during photosynthesis and added to the soil by growing plants. In well managed soils organic matter can be increased , creating a soil carbon sink.

Carbon exists in soils in many different forms. Soil organic matter is part of the carbon cycle and life cycle of eco-systems on land. Lime, gypsum and ash, are mineral forms of carbon in soils.

Plants are made from sugars, starches, cellulose, fats and oils, proteins and lignin. Sugars are very quickly eaten by microorganisms, cellulose is slowly converted to sugars and lignin is very resistant to decay and may survive in soils for hundreds of years. Organic matter in soils is mainly dead, decomposing plant material. Only a small proportion originates from animals. Animal bones, CaCO3 is an important animal Carbon compound.

Organic mater in soils is found in varying stages of decay. On the soil surface plant residues occurs including leaf litter and mulches. Particulate organic carbon is small plant remains and humus is very small particles synthesized by microorganisms. Charcoal is resistant organic matter and can last in soils for thousands of years.

Increasing the amount of organic matter in soils helps to build a vibrant, healthy, living ecosystem.

Benefits of Organic Matter

Soil structure is improved,

Bulk density decreases,

Water infiltration is faster,

Porosity is increased,

Drought resistance improved,

Water holding capacity increases,

Higher cation exchange capacity,

Growing plants increases the root density in soils and the tips of roots add exudates into the rhizosphere where microbial activity is high.

Native bush with large trees and an extensive understorey will store carbon above and below ground level. Very little original bush remains in old Sydney suburbs and now bush regeneration enthusiasts and councils are planting native vegetation in parks and gardens.

Well managed garden soils will contain up to 10% organic matter and the carbon content of organic matter equals 58%.

In Australia a dense vigorous native bushland can store 260 tonnes of carbon per hectare. In most forests ½ of this carbon is stored in the above ground plants and ½ is stored below ground in the soil. Wetlands store large amounts of carbon.

Soil organic matter is low in tropical soils and higher in colder climates. Organic matter decomposes quicker at higher temperatures. In very wet environments organic matter decomposes very slowly. For these reasons peats form in alpine soils and swamps. Organic matter in alpine soils and peats may reach nearly 100%.

Irrigation will increase plant growth and carbon storage. In urban areas excess water runoff during heavy rain can be harvested for irrigation of planted bushland. Irrigation of tree lined valleys will increase carbon storage, reduce flooding and pollution from stormwater runoff. Biodiversity will improve when plants are grown along creek valleys forming green corridors.

Detention ponds used to store excess stormwater runoff can be planted with trees.

In a backyard garden it is possible to achieve a high soil organic matter content. Soils containing 10% organic matter to a depth of 30cm will store 240 tonnes carbon/hectare. It is possible for 100 square meters of garden soil to store up to 2.4 tonnes of carbon.

Composts, mulches, manures, and suitable organic fertilizers increase soil organic matter. Digging soils and leaving soil surfaces bare will reduce organic matter. All plant material collected while gardening should be returned to soil. Addition of organic matter to soils improves water infiltration, water storage and help drought proof soils. Water runoff collected from the roves of houses should be stored in water tanks and overflow directed onto the garden.

Organic gardening, permaculture, biodynamic systems, and no dig gardening are useful methods to use in the backyard to help increase soil organic matter.

Fertile garden soils rich in organic matter will increase carbon storage and encourage healthy plant growth. Hungary little microbes eat fallen leaf litter allowing plant nutrients to become available to growing plants. Small soil animals distribute nutrients by eating, moving around and depositing body wastes deep in the soil. Healthy soils are teaming with bacteria, fungi, actinomycetes and tinny critters all eating fallen leaf litter and eating each other.

A small gum tree in a back yard could store up to 1 tonne carbon with 1/2 above ground ground and ½ in the soil. It should be possible to store 4 tonnes of carbon in 100 square meters of garden containing several trees.

An example of carbon storage in an urban garden

Containing 2 trees and 100 square meters garden

Trees above ground 1tonnes

Tree roots 1 tonne

Small plants above ground 1/2 tonne

Small plants below ground 1/2 tonne

soil organic matter 1 tonne

Total 4 tonnes / 100 square meters backyard garden

If 1,000,000 backyard gardens in Sydney stored an average of 4 tonnes of carbon, a large carbon sink totaling 4,000,000 tonnes will be created. It will take several years for trees to grow and soil organic matter to build up and produce a large carbon sink. Extra carbon could also be stored in Council Parks and gardens.

A significant amount of carbon can be stored in the backyard and a enthusiastic green thumb could store in the soil and trees all of the carbon emissions produced in an energy efficient home. The backyard soil and garden can become an important component of a carbon neutral home.

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Soil Organic Matter

Soil Carbon, Carbon Cycle & Carbon Sinks
Soil organic matter is the decaying remains of plants and animals and consists of carbon compounds.

Organic matter is important in forming healthy fertile soils. Plant nutrition and soil physical properties are improved in soils containing an adequate supply of organic matter.

Soils are a very good carbon sink and have the potential to reduce the adverse effects of global warming. Carbon dioxide is released into the atmosphere from decomposing organic matter and is absorbed during photosynthesis and added to the soil by growing plants. In well managed soils organic matter can be increased, creating a soil carbon sink.

Carbon exists in soils in many different forms. Soil organic matter is part of the carbon cycle and life cycle of eco-systems on land. Lime, gypsum, ash, charcoal, are mineral forms of carbon in soils.

Fertile soils provide an ideal medium for the healthy growth of many lifeforms. Most plants obtain water and essential nutrients from soils. Many small animals including worms, mites and insects live in the leaf litter and surface soils. A small number of large animals including wombats and rabbits burrow into soils to make their family home.

Fertile soils are teaming with invisible microbes. Soils are an ideal home for, bacteria, actinomycetes, algae, protozoa and fungi. Many plant roots and microbes form special interactive relationships. In the rhizosphere surrounding plant roots, exudates containing food for microbes are released by roots encouraging prolific microbial growth. The microbes help the roots to absorb nutrients.

Small soil animals and microbes continually break down soil organic matter into gaseous CO2, water and minerals. The decomposition of organic matter releases essential mineral elements into molecules available to growing plants. Nitrogen, phosphorus and sulphur are important plant nutrients continually added to the soil by the decomposition of organic matter.

There is a continual cycle of carbon without the build up of large amounts of dead plant material. The accumulation of peat in swamps and the ancient formation of coal and oil occurs when the environment is unfavorable to micro-organisms.

Organic matter is made up of partly decomposed plants and humus. On the soil surface their is a layer of leaf litter. Many small animals, especially insects and worms eat the fallen plant material and deposit faeces rich in nutrients deeper in the soil. Many microbes feed on organic matter and then eat each other.

Humus.
Humus is completely decomposed organic matter and cannot be recognized as plant remains. Small humus particles are amorphous colloids, smaller than crystalline clay colloids and the surface is electrically charged and attracts cations and anions. Many essential plant nutrients are stored on the electrically charged surface of humus helping to improve soil fertility. Water is absorbed by humus increasing the ability of soils to store water.

The dark colour of soils, especially top soils is due to dark coloured humus. The presence of humus tends to give soils a healthy, fertile feeling. A healthy soil contains 10% or more organic matter in the top soil and the sub soil may only contain 0.5%.

Leaf Litter
Leaves falling onto the soil surface build up a layer of leaf litter. Leaf litter is a very dynamic eco-system with many small animals and microbes. The leaf litter and soil is natures recycling centre where small animals and microbes eat fallen plant material releasing nutrients into a soluble form which is available to growing plants.

A healthy, dynamic leaf litter also improves the physical fertility of a soil. Small soil animals and microbes create good soil structure improving soil aeration, increasing water infiltration and reducing extreme temperatures. Burrowing animals, especially earthworms greatly improve water infiltration. Leaf litter protects surface soil from beating raindrops and erosion. A deep leaf litter is a natural mulch and is food for earthworms, every gardeners friend.

Mulches
Leaf litter on the surface of soils is natures perfect mulch.

Mulches are a layer of loose plant material or other residue spread on the soil surface to help conserve moisture. Common materials used for mulching are wood or bark chips, straw, animal manures and compost. Garden waste if chopped into small pieces makes a good mulch. Artificial materials are sometimes used as a mulch. A layer of black plastic, paper or small stones will stop weed growth and conserve moisture.

Mulches made from plant material will be eaten and broken down by soil animals and microbes and incorporated into the soil organic matter. The speed of breakdown varies greatly depending on the mulch. Wood chips breakdown slowly and remain on the surface for a long time. Straw from horse stables will breakdown more quickly if it contains animal manure. Many mulches, especially mulches containing animal manures will add plant nutrients to a soil when they are broken down and buried in the soil. It is important not to introduce weed seeds or diseases to the garden from mulching.

Peats
Peats have a very high organic matter content and form in swamps or cold climates when the decomposition of plant material is very slow. The organic matter content ranges from 40% to 90%. When the rate of plant growth is faster than the rate of decomposition, organic matter will accumulate and a peat will form.

In many natural ecosystems peats help to regulate water flow in creeks and rivers. Water is stored in peats, reducing flood peaks and during dry times water is released maintaining streamflow during droughts. Peats are famous for purifying water and the best Scotch Whisky is made using pure, fresh water flowing out of the highland peats. In the Blue Mountains of NSW, many hanging swamps help to regulate water flow in mountain streams.

Microbes
Soils are an ideal medium for microbes to grow in. Bacteria prefer to grow in the thin layer of moisture surrounding clay particles and fungi grow better in large soil pores and can survive in dry conditions. Bacteria have a diameter of approximately 0.001 mm and fungi filaments about 0.005 mm. In comparison clay particles are less than 0.002 mm.

Microbes need a continual supply of food from plants and animals. Different microbes eat different plant materials. Bacteria prefer to eat smaller soluble compounds, especially sugars. Fungi feed on hard to decompose plant fibers and woody material including cellulose, lignin and plant fibers.

Benefits of soil organic matter
•Food for microorganisms and soil animals
•Nutrient cycling
•Store plant nutrients in soils
•Reduce harmful changes in soil acidity and alkalinity
•Improve soil structure
•Reduce erosion
•Increase water infiltration
•Improve water holding capacity
•Create healthy soils and encourage vigorous plant growth
•Are a very good carbon sink and reduce greenhouse gases
A gram of healthy soil contains up to 3,000 million bacteria and 500,000 fungi plus actinomycetes, algae and protozoa.

Microbes generally grow faster in fertile soils similar to the ideal conditions for plant growth. The soil needs to have adequate moisture, aeration and good drainage. Most microbes need similar inorganic nutrients to plants. Nearly all microbes differ from plants and cannot manufacture organic material by photosynthesis and need a supply of organic matter to grow on.

Healthy soils with dynamic microbial ecosystems are able to break down many organic pollutants.

Small soil animals
(Mesofauna or Invertebrates)

Most small soil animals are found in the leaf litter and top soil. Good soil aeration is needed for optimum growth and waterlogging greatly reduces the survival of animals. Insects, mites, spiders, centipedes, millipedes, earthworms and nematodes are found in soils.

Plant Roots
Roots anchor plants and stop them from falling over or blowing away and they absorb from the soil water and nutrients essential for growth.

Plants with deep roots can tap a larger reservoir of water and are more drought resistant. Plants with a shallow root system can only absorb water from the surface soil and are more susceptible to droughts.

Perenial plants with deep tap roots may have roots up to 40 metres deep. Annual grasses have shallow fibrous roots and the lawn grass Poa annua have roots only 15 cm deep.

Roots do not penetrate into dry soils. When watering plants sufficient water should be applied so the water wets the soil to a depth a little greater than the root depth. Plants should be encouraged to grow deep roots and to become drought proof.

Rhizosphere
The rhizosphere is the zone of soil surrounding roots containing a large, very active population of microbes. This microbial active zone can extend up to 1mm from the root.

Root exudates and secretion of border cells
Plant roots exude water and many organic chemicals including sugars, amino acids, organic acids, vitamins, plant hormones, growth substances, mucilage and proteins. Special chemicals can inhibit growth of pathogens and competitor plants. Benificial microbes are encouraged by exudates.

Up to 20% of carbon fixed by photosynthesis in plants is transfered to the soil as root exudates.

Exudates regulate microbiological activity and encourage beneficial symbiosis. Microbiological activity encouraged by exudates improves the uptake of nutrients by roots. Exudates defend roots from pathogens, reduce diseases and inhibit growth of competing plants.

Rhizophere and exudates improve water conditions in soils encouraging plant growth. Fungi filaments and mucilage stabilise soil aggregates and improve soil structure.

LIFE IN SOILS

More living matter and diversity grow below ground level. Fertile soils provide an ideal medium for the healthy growth of many lifeforms. Most plants obtain water and esential nutrients from soils. Many small animals including worms, mites and ants live in the leaf litter and surface soils. A small number of large animals including wombats and rabbits burrow into the soil to make their family home.

Fertile soils are teaming with invisible microrganisms. Soils are an ideal home for, bacteria, actinomycetes, algae, protozoa and fungi. Many plant roots and microrganisms form special interactive relationships. In the rhizosphere surrounding plant roots, exudates containing food for microrganism are exuded by the roots encouraging prolific microbial growth. The microbes help the roots to absorb nutrients.

Organic matter

Soil organic matter is the decaying remains of plants and animals and consists of carbon compounds.

Small soil animals and microrganisms continually break down soil organic matter into gaseous CO2, water and minerals. The decomposition of organic matter releases essential mineral elements into compounds available to growing plants. Nitrogen, phosphorus and sulphur are important plant nutrients continually added to the soil by the decomposition of organic matter.

Fertile soils are dynamic ecosystems with growing plants continually adding organic matter to soils and lifeforms continually eating and converting the dead plant remains into compounds available to new growing plants. There is a continual cycle of elements without the build up of large amounts of dead plant material. The accumulation of peat in swamps and the ancient formation of coal and oil are excemptions to the rules of decaying carbon cycles.

Soil organic matter
Organic matter is made up of partly decomposed plants and humus. On the soil surface is a layer of leaf litter. Many small animals, especially insects and worms eat the fallen plant material and deposit faeces deeper in the soil. Many microorganisms feed on organic matter. Bacteria live in the film of water surrounding clay particles and preffer to eat soluble compounds, especially sugars. Fungi preffer to live in large pore spaces and feed on hard to decompose organic compounds including cellulose, lignin and plant fibres.

A healthy soil contains 10% or more organic matter in the top soil and the sub soil may only contain 0.5% .

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Early Environmental Articles

by Ted

The Soil-Greenhouse Connection

Discussion Paper, Friends of the Earth(Sydney)

Prepared by Ted Floyd

Oct 1989
When discussing the role of carbon and carbon dioxide in causing the Greenhouse effect little attention is paid to the importance of the soil as a major source of carbon.

The major Greenhouse gases and their relative importance are carbon dioxide 50%, chlorofluorocarbons 25%, methane 10%, ozone 10%, and nitrous oxide 5%. For carbon dioxide 75% is contributed by burning fossil fuels and 25% by destruction of vegetation.

It is obvious that the major source of carbon dioxide is fossil fuels but the destruction of vegetation is also a major source of greenhouse gases. In the minds of most people, the destruction of vegetation conjures up visions of forests being cleared by burning and all that beautiful timber going up in smoke and carbon dioxide. This is partially correct but what is not emphasised is the slower, less obvious process that occurs in the soil, where soil microorganisms break down soil organic matter and the end result of respiration by these microbes is carbon dioxide.

Balance exists as long as the ecosystem is not disturbed. Before I discuss some of the consequences of disturbing this balance I will try to emphasis just how much carbon is stored in soils.

In the following table the total amount of carbon stored in the various earth reservoirs is listed.

Reservoir 10x 15 g Carbon Stored

Atmosphere 712

Living organisms 830

Soil surface litter 60

Soil 1500

Peat 160

Surface water 728

excludes deep sea sediments and fossil fuels etc.

From this table it can be seen that the soil is a very large reservoir of carbon and for example there is nearly 2 x as much carbon in the soil than in living organisms.

Generally the ratio of carbon stored in above ground portions of an ecosystem to that stored below ground is dependent on the climate, mainly temperature. The colder the climate the more carbon is stored below ground. For example, tundra ecosystems have up to 90% of their carbon stored below the ground surface and 10% above ground level. A tropical rainforest may have 25% of carbon below ground surface and 75% above.

Grasslands can have a very high proportion of their carbon stored below ground. Up to four times their carbon can be stored below ground compared with above ground.

I hope I have shown that soil organic matter is important and though you can not see the organic carbon in a soil it is as important as the majestic tree which can be admired. When discussing the effects of destroying vegetation on the greenhouse effect, the important role of the soil must be considered.

We will consider a mature native forest that was in complete balance with carbon dioxide absorbed equaling carbon dioxide respired by animals and microorganisms. In this forest up to 75% of the carbon can be hidden away underground and 25% of the carbon stored above ground in the fine forest that we can see and walk through.

The foresters who love to chop down these trees also only see the fine timber above ground level. They argue that if they chop down these trees, they will grow again. Then the foresters argue that since trees are growing they absorb carbon dioxide and they are solving the greenhouse effect. Stop! Lets dig a little further into this argument.

In the native forest a large store of organic matter has built up. In the native forests the trees, bushes, grasses, etc. continually add organic matter (leaf litter) to this store. Similarly the soil microbes break this organic matter down. There was a balance. Organic matter added to the soil equaled organic matter broken down by microbes.

When the forest is cut down, the addition of organic matter to the soil is drastically reduced. The microbes are still there, they still continue to feed on the remaining organic matter. The difference now is that as the soil microbes break down the soil organic matter, little additions are made to this store from the cut down forest. The end result is the total store of soil organic matter decreases and this adds to the carbon dioxide released to the atmosphere, i.e. the greenhouse effect is exacerbated.

This effect of depletion of soil organic matter can last for many years after the cutting down of a forest. A study by the University of Western Australia showed that surface soil organic matter reached a minimum of 40% of original forest soil after 7 years of clearing. Even after 100 years the soil organic matter of a cleared forest was only 80% of the original forest.

Different farming methods can have a very important effect on the level of organic matter in a soil. Generally while land is under pasture and is not cultivated organic matter builds up, compared to cultivated land. When a crop is grown such as wheat, the soil is cultivated and generally the level of soil organic matter falls.

Usually when growing wheat a rotation is used where for some years wheat or similar crops are grown, then the land is placed under pasture, usually a mixture of legumes and grasses which is grazed by sheep or cattle.

The type of rotation has an important effect on the level of organic matter in the soil. If there is many years of wheat and a few years of pasture, the soil organic matter falls. It is important to have sufficient years of pasture in the rotation to maintain adequate levels of organic matter.

Falls in the level of organic matter during farming, will release carbon dioxide to the atmosphere and will be a contributing factor to the greenhouse effect.

The magnitude of this problem can be visualized from the following hypothetical example. A farm soil has in the top 10cm an average of 5% organic matter. After intensive farming the level of organic matter is reduced from 5 to 4%. From the decomposition of this organic matter 27,000 kg of carbon dioxide is released to the atmosphere. For comparison, the average Australian car produces 3,500 kg of carbon dioxide a year. Of course the opposite is true, i.e. if a good farmer increases the organic matter in the soil, carbon dioxide is absorbed.

Good farmers know there is many advantages in increasing the organic matter in a soil. The soil has a better structure, water infiltrates better, aeration is better and especially, soil erosion is reduced. Now it is important to maintain or raise organic matter so as to help in the global battle to reduce the greenhouse effect.

born 18th Aug 1946 at summer hill, sydney australia school north junee primary yanco agricultural high school leaving certificate 1963 sydney university facultary of agriculture major soil science 1964 to 1968 BSc Agr web. www.ramin.com.au/creekcare