This week in Saturday Swot Shop I’m looking at the different textures of soil.
There are 3 main types. Sand, Silt and Clay. Each has a different particle size. It’s particle size which determines how the soil will handle moisture and heat.
Sandy soil has the largest particles, giving it a gritty feel. Water drains easily through it, too easily, washing away nutrients with it. Sandy soil warms up quickly when the sun arrives.
The size of silt particles sits between sand and clay. Smooth in texture, it balances holding on to moisture whilst draining away the excess.
Clay soil has the finest particles of the three. It drains poorly, retains water and between the tiny particles there is little room for air, meaning plant roots struggle for oxygen. Sticky when wet; cracked and baked when dried out. Its dense texture makes it slow to warm up.
One, two or a combination of all three will make up most of a soil.
But to create fertile soil, organic matter (humus) also has to be present. Air and water are the other constituent parts.
So where does the magical loam feature ? Magical because it retains moisture whilst allowing water to flow freely, retains nutrients, allows air to circulate and is straightforward to work.
Loam refers to a soil containing a particular combination of sand, silt and clay. The only problem being is I can’t find a definitive equation.
Blends are stated as 40 % sand, 40% silt, 20% clay, or equal parts of each.
A sandy loam would seem to mean that the greatest part of the mix of all three was sand and so on…
So I looked up what I’d get if I bought in some luxurious looking top soil, the sort you hold between cupped hands and gaze upon with earthy reverence. It was described as sandy loam, an organic content of 6% and particle size no larger than 20mm.
Updated – The site in question actually refers to screened to 2omm, which thanks to Broken Chalks’ comments makes me realise I have misunderstood something , somewhere along the line.
These are particle sizes ( diameter) as defined by the Soil Survey body:
- Gravel greater than 2.0 mm
- Coarse Sand between 0.6 and 2.0 mm
- Medium Sand between 0.2 and 0.6 mm
- Fine Sand between 0.06 and 0.2 mm
- Silt between 0.002 and 0.06 mm
- Clay less than 0.002 mm
Apologies for the confusion and thanks for the feedback !
{ 3 comments… read them below or add one }
That last part – a particle size no larger than 20mm – can’t be right.
Hello,
Oh dear – it is quite possible that I’ve misunderstood something. Dirt Dentenion here I come !
I looking at the detail on the Rolawn topsoil site and it said screened to 20mm and in my mind I read it as sieved to 20mm…. but I may have made an erroneous connection.
I will investigate further – here;s the link if you want to do a bit of dirt drooling ! – it’s lovely looking stuff !
Perhaps it is right, then – 20mm is rather large, though; I must be putting in too much effort when I’m raking away trying to get the garden to look even and vaguely ready to put seeds in!