To the uninitiated the soil under our feet is a lifeless, uninteresting dirty media which sticks to their boots and soils their clothes. To us gardeners, there beneath us lies a vast biological factory and nutrient reserve, which must be nurtured, restocked and cultivated. Apart from the obvious soil fauna, i.e. insects and earthworms of which there are ten common species in Britain, depositing an extra 5mm. of topsoil per hectare per year, in the form of wormcasts. There are also vast numbers of bacteria, estimated at 1,000 million in each gram of fertile soil and despite their microscopic size the top 150mm. of topsoil carries about one tonne of bacteria per hectare.
SOIL FORMATION:
Soil is formed by a number of evolutionary changes taking place,
the most important of which is weathering. From the moment rocks
are formed and exposed to the elements they are subjected to erosion
and the movement of rock fragments in the soil. Weathering
can be further split into two main causes:
PHYSICAL WEATHERING: Which is the action of rain, snow, sleet,
wind and flowing water, also alternate freezing and thawing.
CHEMICAL WEATHERING: Rainwater is a weak acid (Carbonic Acid)
which dissolves Limestone. Plant roots also produce weak acids.
Oxygen reacts with many rocks to make them crumble, (a similar
process to rusting). The decomposition of organic matter produces
a weak acid.
All these various factors are instrumental in the fragmentation
of rock which is the first stage of soil formation. Plant roots
then explore the small fissures in the rock and prize them wide
open. The plants die and then bacteria work on the remains, and
after thousands of years a living soil is developed.
SOIL TYPES:
Organic soils which are made up of partly decayed plants are called
PEATS. Soil made up of largely inorganic substances,
i.e. different size rock fragments, with some organic matter present
are called MINERAL SOILS.
SOIL TEXTURE: This is usefully defined as the relative proportions
of the sand, silt and clay particles in the soil.
The Agricultural Development and Advisory Service (ADAS.), classify
soils as follows: Sandy - Loamy Sands - Sandy Loams - Sandy Silt
Loams - Silt Loams -Sandy Clay Loams. Clay Loams -
Silty Clay Loams - Sandy Clay - Clay - Silty Clay. Any of
the above soil groups may be formed on chalk or limestone, so
they are given the prefix Calcareous e.g. Calcareous
Clay Loam.
HUMUS: This is essential to maintaining
soil structure. This vital ingredient is a sticky black liquid
which remains in the soil when plant remains (organic matter)
are decayed or broken down by bacteria. It is responsible for
binding together the mineral particles and making the desirable
crumb structure.
Organic matter Used by Earth worms and Bacteria
Bacteria Sticky layer of Humus coats soil particles
Soil Crumbs Overcropping, Overcultivating, Failure to add
O/M, Waterlogging, Erosion, Compaction Loss of Crumb Structure.
SOIL STRUCTURE: This is the process of the arrangement of particles
in the soil. The structure formation turns mineral particles into
crumbs.
Once a soil has Structure, plant roots can obtain
oxygen from large pores and water from the smaller pores. They
also obtain most of their Mineral Foods from the breakdown of
Humus.
PLANT NUTRITION:
In a natural plant community, when plants die, they decompose
and nutrients are recycled and become available to the plants
again. When, however, a crop is harvested and removed from
the soil, the nutrients are lost, and unless returned in some
other form, the soil becomes poor and infertile. Nutrients are
also leached out of the soil by rain.
Growers can take some steps to help prevent depletion of nutrients
by crop rotation etc. but these measures on their own are not
sufficient to meet the demands of intensive growing methods. The
grower therefore has turned to the application of fertilisers.
In order to grow satisfactorily, plants require SIXTEEN
different mineral elements. The ones needed in the largest amounts
are called the Major or Macro Nutrients.
MAJOR NUTRIENTS:
1) Nitrogen: The presence of N. in the soil is the result of bacterial
action Nitrogen fixation, or the addition of artificial fertilisers.
It is almost entirely absent from the bedrock from which soils
are made.
Nitrogen is of extreme importance - found in proteins, chlorophyll,
enzymes and nucleic acids (genetic material).
2) Phosphorus: Most soils contain large quantities of P. but only
a small proportion is available to plants. P. is released from
soil organic matter by micro-organisms but most of it is quickly
converted to insoluble forms by a process called phosphate fixation,
insoluble aluminium, iron and manganese phosphates are formed
at low pH and insoluble calcium phosphate at high pH. Phosphorus
is important in the production of nucleic acid and large amounts
are found in the meristems (growing points). It plays an important
role in respiration and large amounts are found in roots, fruit
and seed.
3) Potassium: It is usually present in sufficient amounts in clay
soils where it is firmly bound, it is readily leached from light
sandy soils. It has no structural role in plants, but is important
in the metabolic processes. It activates enzymes including those
that make proteins. It is important in flowering and fruiting.
4) Magnesium: Mg. is less abundant than calcium and deficiency
may occur on sandy or acid soils. It is required in large amounts
by most plants and the use of magnesium limestone is widespread.
It is a constituent of chlorophyll, and is involved in the activation
of some enzymes and in the movement of phosphorus.
5) Calcium: Present in most soils, and plants seldom suffer from
deficiency. It is important in the formation of plant cell walls,
especially in the meristematic regions where rapid cell division
takes place.
6) Sulphur: Present as the sulphates in many soils and also as
insoluble sulphides of iron which are unavailable to plants. Sulphur
is present in proteins and enzymes.
TRACE ELEMENTS: (Minor or Micro
nutrients)
Boron, Zinc, Copper, Iron, Sodium, Maganese, Aluminium, Molybdenum.
These are present in plants in very small amounts but are just
as essential for healthy growth as the major nutrients. THEY CAN
BE TOXIC if present in too high a concentration. Most mineral
soils have adequate reserves of trace elements.
THE IMPORTANCE OF CORRECT SOIL pH, TESTING and its effect
on NUTRIENT AVAILABILITY:
Nitrogen, Phosphorus, Potassium, Calcium and Magnesium become
more available as pH increases (more alkaline) though Phosphorus
is less available above pH 7. Iron, Manganese, Boron Copper &
Zinc become more available as pH falls (more acid), though Manganese,
Boron, Copper & Zinc become less available below pH5.
Calcium and Magnesium are nutrients which not only become more
available at higher pHs, but are the main components of LIME which
is used to adjust soil pH to a level just below neutral (pH 7)
pH 6.5 is found to be most favourable for the availability of
all plant nutrients and is the pH to which most soils and soil
based composts are adjusted, Nitrifying bacteria work best above
pH 6 therefore Nitrogen is more available.
As the reader can now appreciate the importance of correct pH
is vital to healthy plant growth, and the importance of having
your soil pH accurately measured and obtaining expert advice on
its correction is first priority at the start of the growing
season.
NUTRIENT ANALYSIS:
Growers can as well as having the pH of their soil tested, have
a major nutrient analysis.
We at ROSEDALE TESTING SERVICES, will be happy to carry out this
work. All the gardener has to do is to send a soil sample to us,
(instructions for sample collection etc. is contained in our free
fact sheet, S.A.E. please) telling us which plants are to be grown,
and leave the rest to us.
You will receive, (within 7 working days from receipt of sample)
a detailed test report, containing details of nutrient levels,
actual soil pH, how to adjust if necessary, how to correct any
nutrient deficiencies, with what fertiliser, and in what amounts
using either organic or chemical fertilisers. Also included is
an assessment of soil composition, soil type, and workability
and how to improve if necessary, we will even tell you how much
organic matter it contains at a small extra charge if you require
it.
We test hundreds of samples from all over the U.K. every year
from professional growers to major exhibitors to weekend gardeners,
so you can be assured of a professional service at a reasonable
price with expert advice.
ANALYSIS:
OPTION 1: Standard Analysis. pH - Tests for N, P, K. An assessment
of Soil Composition etc.
OPTION 2: Exhibition Analysis. pH - Tests for N, P, K. An assessment
of Soil Composition etc. PLUS Test for Magnesium and Soil Conductivity,
(Soil Conductivity is measured electricaly and gives a measure
of the salt concentrations in the soil. If salt concentrations
are too high, symptoms of water stress become apparent. Salt concentrations
can occur from over zealous application of fertilisers or in protected
culture, greenhouse or poly-tunnel, which are not exposed to rainfall
etc.)
Also available: ORGANIC MATTER DETERMINATION, results expressed
as a percentage.
If you require any additional information contact me;
To obtain our soil testing fact sheets, S.A.E. please to the
above address.
Click here for the report on my soil, I am situated in west central Scotland.
Here is the report on John Wallace's soil. John lives about 30 miles
east from my location.