Welsh Poultry Centre

Organic Matter and Life

What is organic matter?

The usual definition of organic matter would go somethinglike this: it is the living organisms and the remains of living organisms inthe soil. It would then go on to tell you of its importance in giving the soilstructure, and retaining water and nutrients in the soil.

While this is undoubtedly true I believe it understates thecentral role organic matter plays in terrestrial life on this planet.

The First Life

According to fossil evidence in the earliest rocks found onearth, life first appeared on this planet around 3.8 billion years ago, aroundthe end of the Hadean period and the beginning of the Archean. It is possiblethat life started even earlier, at some point in the Hadean period, but they'rebeing no rocks from that period it is not possible to verify. These firstsingle cell life forms photosynthesised and thus are thought to be responsiblefor the oxygen on the planet. This eventually made terrestrial life possible.

The First Soils

Soil requires rocks to be broken down into their constituentminerals. This process would have been carried out through weather and watererosion but also through the activity of other bacteria and fungi. An importantadaptation of these primary colonisers was the ability to fix nitrogen from theair. One example of an early terrestrial coloniser is lichen. Lichen is acomposite organism consisting of algae and fungi in a symbiotic relationship.The algae obtain carbon (there was plenty of CO₂ back then) and nitrogenfrom the air while the fungi break down the rocks with certain acids to obtainminerals. Thus, over millions of years, soils were formed by life and withlife.

The building blocks of life, the single cell

The earliest life forms on the planet were probably singlecell organisms called prokaryotic, which means pre nucleus. At some point(after around 1.2 billion years of just prokaryotic cells) we arrive ateukaryotic, which means good or true nucleus. All multicellular beings andquite a few unicellular are eukaryotic while bacteria are prokaryotic.

The only main difference between the two is that in theeukaryotic cell the DNA is wrapped up in a distinctive membrane or nucleus,which is absent in the prokaryotic cell. All life on the planet is made up ofthese cells with the only difference being the DNA code, (and even thatdifference is surprisingly small). The human body has about 60 trillion ofthem. Interestingly the human body probably has ten times that amount of bacteria cells as well in andon it.

About 40-50% of each living cell's dry weight is made up ofcarbon. The biomass of the planet, measured in just carbon and not includingbacteria is around 600 billion tonnes, of which humans make up about 100million tonnes, (Atlantic krill make up 500 million tonnes!). Estimates of howmuch biomass resides in bacteria suggest that this would make up another 600billion tonnes, although nobody really knows and more and more bacteria arebeing found all the time. What does appear true is that a large percentage ofthose bacteria are found in soil. It is estimated that a gram of soil holdsbetween 40 to 200 million  bacteria(I know, a very wide range, but it depends on a lot of variables).The actual function of all the bacteria is still largely unknown. However,thinking of them as "pre" (prokaryotic) to the "good" (eurkaryotic)underestimates them. It is becoming apparent that they often work together toachieve an aim. For instance it requires 600 species of bacteria, working inunison, to a attack and decay the enamel of your teeth, the hardest substancein your body.

Soil and human beings, we need each other!

It would seem to me that we human beings have, and all lifehas, a symbiotic like relationship with soil organic matter. We could not existwithout it and without life there would be no soil, just a bunch of minerals.Soil is the engine which drives the carbon cycle of which we, along with allother life on the planet are a part. Just like life forms, organic matter isaround 40-50% carbon. When talking about soil organic matter we are alsotalking about carbon.

Carbon

Carbon (C) is the fourth most abundant element on the planetand forms the basis for most living organisms. It is fundamental to livingorganisms because it has the ability to bond with other carbon elements intolong chains and thus build complex molecules. It also has the ability to bondwith other elements, such as oxygen. In its purest, or nearly purest state,carbon is a diamond, one of the hardest objects, and in a different structure,graphite, which is one of the softest.

When referring to climate change or carbon footprint, wemean carbon dioxide, (CO₂) which is one element carbon and two oroxygen. This is the form that carbon takes at one stage of the carbon cycle.The carbon cycle is the movement or rotation of all carbon elements. Carbonisn't produced, merely recycled. So, for instance the carbon in a piece of woodcould be burnt, thereby releasing that element into the atmosphere bonded with2 elements oxygen, (CO₂). Through photosynthesis that same carbonelement is separated from the oxygen, which is released back into theatmosphere and becomes part of the plant. Once within the plant, through theactions of various enzymes and hydrogen from water (H2O), the same carbon atombecomes part of a glucose molecule, (while releasing oxygen from the water).The energy for this photosyneytsis of course comes from the sun.

It takes 15MJ of the sun's energy to produce 1kg of glucose.If that amount of energy weren't used in this way it would have a warmingeffect. In this way photosynthesis is a cooling process, (why a town is hotterthan the countryside, the heat is reflected rather than absorbed).

How the sun fuels life on earth

Resynthesis is the process by which the simple sugars arereformed into a variety of organic compounds, including carbohydrates, proteinand organic acids. The sun's energy, through the process of photosynthesis,provides the fuel for life on earth. Carbohydrates such as cellulose provideenergy for grazing animals, the starch in grains provide the energy forlivestock and people and the carbon stored from past eras, (hydrocarbons), inthe form of oil, coal and gas provide the energy that runs our transportsystems, produces our fertilisers (soluble), pesticides, plastics, metals andso on.

Carbon is basically food for the microbes in the soil. It ismicrobes that drive the powerhouse that is soil. Through their actionsnutrients availability is enhanced. Soil would be lifeless without them andthey require carbon to survive. Through a process called exudation around30-40% of the carbon taken from the air and fixed by the plant is exuded intothe soil to provide the food source for microbes that in turn allow the plantto better utilise the nutrients within the soil. The amount of active greenleaves present and therefore the volume of roots govern the carbon added to thesoil in this way. The more plants the more carbon is added.

Humus

Organic carbon is relatively transient, it moves through thesoil. Humificaton is the process by which soil microbes convert carbon intohumus. Humus, a gel like substance, is organic matter that has reached a pointof stability. It has the ability to hold four times its own weight in water,improves soil structure by allowing spaces between the soil particles andappears to be able to hold plant nutrients in an available form. The exactnature of humus is not, even now, fully understood, however it is known thathumuification can only occur if there is a continuous supply of food, (carbon)for the soil microbes. If it does not occur then the carbon exuded by the plantroots (or added to the soil in the form of manures) simply oxidise back intothe atmosphere as carbon dioxide.

How fungi in the soil help lock up carbon

As well as soil microbes and bacteria it has become apparentin recent years that soil fungi also play an important part in production ofstable organic carbon stored within the topsoil. Most perennial grasses aregood hosts for mycorrhizal fungi. This fungus attaches itself to the grassroots and takes some of the sugars that the plant produces. In return the fanlike network of the fungus, called hyphae, thinner than a hair, push out intothe surrounding bulk soil many metres beyond the plant roots. The absorptivearea of the fungus is approximately 10 times more efficient than that of roothairs and about 100 times more efficient than that of roots.

The fungus appears to play an important part in theproduction of humus and also the production of something called Glomalin. Ituses Glomalin to coat the hypea, thus protecting it. Glomalin is, in itself ahighly stable form of soil carbon, which it is estimated in some area (hotterclimates and low clay type soils) to make up a third of all soil carbon. This amazingrelationship is inhibited by the use of soluble fertilisers, pesticides andground that is left bare.

Losing soil carbon

Soil carbon is the biggest terrestrial pool of carbonworldwide. It is estimated at 2700 gigatonnes (Gt), although this figure is continually being revised up. Atmosphericcarbon is estimated at 780 Gt. In the UK the latest figure suggest that we arelosing nearly 1% of soil carbon per year, around 13million tonnes per year. Inwarmer climates oxidisation occurs more rapidly, Australia has lost around70-80% of its soil carbon in the last 100 years. The loss of carbon, the foodfor the bacteria and microorganisms, also means a decline in their numbers.They are also carbon-based life forms. It is estimated (although this appears tobe no more than a guess), that between 50-80% of atmospheric carbon comesdirectly from losses of soil carbon.

The Impact

Soils are less able to retain water. Last spring we had drought conditions in theeastern half of the UK. The average organic matter content of these areas isaround 1% now. The lower rainfall was not the only reason there were droughtconditions. Years of mono cropping has led to low organic matter resulting insoils unable to retain moisture.

Increased erosion. Atthe moment around 3 million tonnes of topsoil are being lost in the UK everyyear. Globally, a UN report estimated that 10 million ha are degraded or lostas rain or wind erode the topsoil each year.

Increased flooding.It is not just the changing climate that creates more floods. Soils withoutsufficient organic matter cannot retain water, consequently, run off isgreater. This creates problems for watercourses that cannot handle the suddenvolume of water.

Increased climate change.If the carbon isn't locked up in the soils then it is accumulating in the atmosphere as CO₂,(one carbon and two oxygen combined). The effect of this is to preventinfrared radiation escaping from the planet which has a warming effect. Methane(CH₄, 1 carbon and four hydrogen) has 20 times the Global WarmingPotential (GWP). However, methane lasts only 12 years in the atmosphere,compared to  CO₂  which lasts between 50 and 200 years.

Loss of soil structure.Take away organic matter and you have a bunch of minerals. Take away asignificant amount of the organic matter and you have fragile soils that aremore easily damaged by machinery, or weather.

Loss of nutrients.Without soil carbon the life activity of the soil declines. The amazingrelationships explained above don't happen. Plants don't have the ability tofully exploit the soils and even soluble fertilisers pass through the soil andinto the watercourses quickly. Few soils are deficient in actual phosphate.Most contain sufficient reserves to support plant growth, if they were made available.However, to make them available we have to reverse the decline in organicmatter, we have to start looking at the health of the soil rather than lookingat the health of the crop. It is estimated that each year in the UK 172,000tons of phosphate and 123,000 tons of potassium are flushed into our river andsea. We then import 700,000 tonnes of North African rock phosphate and potash.

A quick look at the fate of a number of past civilisationson this planet should teach us something. They have all declined when they havedegraded their topsoils. The difference today is that we are a globalcivilisation and there are no new soils to exploit.

Since the discovery of a means to fix nitrogen from the air(see nitrogen article) we have started to feed the plant and not the soil. Thisled, initially to huge gains in yield, which fuelled a population explosion. In1950 the world population stood at 2.5 billion, it has recently topped 7billion. Hydrocarbons have made it easy to assume that we can ignore propercrop rotations and feed a crop continuously from a bag, concentrating on theplants nutrition rather than the soils health.

We, as a species, have lost touch with what we are and wherewe come from. We are a carbon-based life form; we are 65 trillion individualcells and we are a product of the soil. The father of soil science, FriedrichAlbert Fallou wrote in 1862:

"There is nothing in the whole of nature which is moreimportant than or deserves as much attention as the soil. Truly it is the soilwhich makes the world a friendly environment for mankind. It is the soil whichnourishes and provides for the whole of nature; the whole of creation dependsupon the soil which is the ultimate foundation of our existence"

©Stephen Merritt, The Welsh Poultry Centre, 2011

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About theauthor

Stephen Merritt is a partner in The WelshPoultry Centre and an accredited advisor and board member of The Institute ofOrganic Training and Advice and has spent over 30 years working in sustainableagriculture in developing countries, England and Wales.  In the last 8 years Steve hasspecialised in free range and organic poultry production and now offers on farmadvice and training to this sector.