How Many Main Types of Soil Exist? Are There 3, 5, 6, 8, 10 or Even 12 Main Types of Soil. In This Article I Explain The Main Soil Types & Where Soil Comes From.
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What Are The Three Basic Soil Types?
If you break solid particles down by size you will see there’s every size under the sun. From rocks and large stones right down to microscopic grains. But the simple way to look at it is to sieve out all the rocks and stones and see what’s left.
There’s still a huge range of particles. In simple terms, there are large particles, middle-sized particles and really small particles. Pedologists, being quite systematic have made it even simpler. They call these sizes sand, silt and clay. Sand is everything that measures between 2 mm down to 0.05mm in diameter.
Silt measures between 0.05mm and 0.002 mm.
Clay is everything that’s smaller than 0.002mm in diameter.
That means that clay is made up of incredibly small particles. The particles will pack together really closely with little space between the individual particles. When clay gets wet it’s really hard for the water to drain away and when it gets dry it is difficult for water to get back into the small spaces, and so it sets like concrete.
Sand is the opposite. Being larger grains it can’t pack together tightly. So there is loads of space between the particles and water drains right through it.
What Are The Five Types of Soil?
We know the first three are sand, silt and clay.
But there are two others that are common in parts of the country. In parts of the country, the soil and the underlying rock is white. An example of an underlying rock that is white is the White Cliffs of Dover. Within a few miles of my home here in south-east Devon, some of the cliffs are red sandstone and others are white. When these white rocks break down they produce chalk soils.
Vast areas of the county have chalk derived soils. For example, Salisbury plain consists of 300 square miles of chalk plateau. And south of Cambridge we have chalk outcrops forming the Gog Magog Hills and beyond. Chalk is very porous so are dry soils.
The Cambridge area of England is fascinating from a geology and soils point of view. To the north of Cambridgeshire, we have heavy clays that are used in brickmaking. To the northeast, the Fens are peat derived. In places, the peat goes down many metres to a clay base. So they hold water and, when drained, are highly fertile.
To the west, as the landscape changes and we enter Bedfordshire the soil type changes again. The small town of Sandy lives up to its name, for here the soil is extremely sandy.
The soils around Sandy are familiar to me as my market garden was at Potton, just a couple of miles from Sandy Later I managed the Cambridgeshire Agricultural College farms that encompassed land in each of these soil types. We had each type of soil to demonstrate the techniques required by the different soil types. It would take me several hours to travel around the different land holdings that the farm comprised. It was a long trip from Cambridge in the south, up the A1 to Sawtry and then across the brick lands to Wisbech which some people see as one of the main horticultural areas of England.
What Are The Six Types of Soil?
I’ve mentioned five types of soil so far. Sand, Chalk, Peat, Clay and Silt soils. And you might think that I meant they exist in isolation. That soil is one or the other of them. But that isn’t the case. Over time, geological events have has mixed them together. And when they thoroughly mix we get a loam soil.
And to make it slightly more interesting we get sandy loams, silty loams .. well perhaps as many types of loam as you have fingers.
An example of the mixing of soil types is seen near my home. The local pebble bed heaths consist of sand and large round pebbles, hence the name. They formed when millions of years ago a huge river swept stones across the landscape. This was long before the English Chammel formed and the continent that became Europe was huge. As the stones were swept along they clashed together and became rounded pebbles. In time this vast river slowed and the sand in the water was deposited in huge beds. In places they were hundreds of feet deep. Littered into those beds were pebbles. Eventually, the river took another course and we were left with the deposits that in time became heaths and uplands such as Woodbury Common.
Today the Pebble Beds extend to the where the sea now is and the pebbled beds have formed cliffs that, as they erode, deposit sand and pebbles. These are swept on the currents to form pebble beaches and sandy beaches, in places such as Budleigh Salterton and Exmouth. Over the years these beaches move, they grow and contract with each storm. Eventually, if the sea recedes, they will become the basis of the new land and will be its soil. If the sea level increases they will form the sea bed, but could become the land in millions of years.
What Are The Nine Types of Soil?
Some websites talk about there being 9 or even 10 types of soil and, in addition to those listed above, they add some quite ridiculous suggestions as to what constitutes a soil.
For example, one site lists hydroponics as being a soil type, then rationalises it by saying sometimes the best soil is no soil at all. Hydroponics is the process of growing plants without soil, so whilst it is possible it isn’t a soil type. Topsoil is another they add, and they make the mistake of saying topsoil is a “commercially produced material that can be used to supplement or replace difficult soil in gardens”. It can certainly be used for that purpose and it is possible to buy it in bags or bulk. But topsoil is naturally produced. As its name suggests, it is the top layer of soil found almost everywhere. It is normally the best soil in the soil profile because it sits on top and has most of the fertility inherent in that soil profile. On occasion, the topsoil is removed by erosion .. or sometimes builders! Gravel is another type of soil mentioned by the same website as the two above occur in. But by most definitions, gravel isn’t soil. The largest constituent in the soil is normally regarded as the sand. Gravel, stones and rocks may occur on a site or even mixed in the soil, but it isn’t soil!
Also listed on the above website is mulch. Mulch can be added to the soil. It is a useful addition and some mulches will ultimately break down to become a soil constituent. But until it breaks down most soil scientists don’t regard mulch as part of the soil. And this assumes it will break down as some people regard a plastic sheet and old carpets as being a form of mulch! They have their uses in the garden .. but are not part of the soil.