Soil organic carbon is organic matter is made up of living organisms,
undecomposed plant, animal and micro-organism residues and humus, formed over
many years. You cannot
have good soil structure without high levels of organic matter.
It is
the main food reserve for living soil organisms and many of them provide the
simple substances that are taken up by the plant roots. The most reliable
method of finding out the soil organic matter (SOM) concentration of a soil is
by burning (dry combustion) at temperatures of over 900⁰C. The result is
normally given as percentage organic matter in the soil. Farmers weekly provide
a simple chart for farmers to score the quality of their soil.
Less than 1% very low
Less than 2% low
Less than 4% Medium
Less than 8% High
Over 8% Very high
 |
Typical components of a soil |
Organic matter is made up of three main
components which have been called the living,
the dead and the very dead!
Living
organisms, plants, animals, soil invertebrates, bacterial and
fungi are all considered to be part of soil organic matter, and they play a big
role in contributing organic residues to the soil and in formation of more
stable types of organic matter. Up to 15% of
soil organic matter is living organisms and fresh organic material.
|
Active soil organic matter is
primarily made up of freshly dead
plant and animal residues that break down in a very short time, from a few
weeks to a few years. It is sometimes called detritus if it contains partially broken down cells and tissues
that are only gradually decomposing. One third to
one half of the SOM is active soil
organic matter, the detritus of partially and slowly decomposing plant and
animal material that may last decades.
Stabilised
or passive soil organic matter, is known as humus. It is very dead(!)
and not biologically active because it provides very little food for soil organisms.
Humus may take hundreds or even thousands of years to fully decompose! Humus is very important as (a) it acts like a sponge and
can absorb 4-10 times its weight in water,
(b) it is a way of taking carbon dioxide out of the atmosphere and
burying it in the ground (sequestering it)
and so helps to mitigate the effects of rising CO2 levels.
 |
| Soil organic carbon from http://soils.usda.gov/sqi/concepts/soil_biology/images/soil_f1_high_res.jpgaption |
Soil organic matter
may enter the soil in a number of ways, such as addition of manure, compost,
mulch such as sweetcorn stalks or woodchip, leaf mould, coffee grounds,
eggshells, chicken pellets or the growing plants in their little pots of
compost. But it may also be produced in the soil by the crop and the
surrounding weeds and soil animals grow and then die and remaining in or on the
soil surface.
Soil organic matter
may be removed from the soil when crops are harvested, often with some sticky
soil around them, on our boots, when the wind blows it away, or heavy rain
washes or leaches it away through the soil.
The global climate is
becoming more unstable due to global warming. Last year it was "the Beast
from the East" for us at HCF, followed by a warm and fairly dry summer.
Who knows what it will be this year? One of our aims at HCF should be to create
a soil that is as resilient as possible to climate change. To be this soil it
needs high levels of Soil Organic Matter. This soil will be able to hold more
moisture, which, among other things, will enable it to cope with longer periods
of water shortage or heavy and excessive rains which would otherwise cause leeching
or runoff.
Refs
http://www.cartage.org.lb/en/themes/sciences/botanicalsciences/PlantHormones/PlantHormones/soil.gifhttp://soils.usda.gov/sqi/concepts/soil_biology/images/soil_f1_high_res.jpg
No comments:
Post a Comment