Soil - components
Physical | Chemical | Biological
Sandy Soil: High proportion of sand and little clay. Also known as light soils, drain quickly after rain or watering, are easy to cultivate and work. warm up more quickly in spring than clay soils. But on the downside, they dry out quickly and are low in plant nutrients, which are quickly washed out by rain. Often very acidic.
Clay Soil: Also known as heavy soils, have over 25% clay, these are potentially fertile as they hold nutrients bound to the clay minerals in the soil and they also hold a high proportion of water due to the capillary attraction of the tiny spaces between the numerous clay particles. Easily compacted when trodden on while wet and they bake hard in summer, often cracking noticeably.
Silt Soil: Features medium-sized particles, fairly well drained and hold more moisture than sandy soils, but are easily compacted and is quite fertile, though it compacts easily.
Loam Soil: A balanced mix of sand, silt, and clay; it is fertile, drains well and easily worked. Widely considered the best soil for gardening. They can be clay-loam or sandy-loam depending on their predominant composition and cultivation characteristics
Peat Soil: High in organic matter and very dark, it is spongy, holds plenty of moisture, and is naturally acidic. They are seldom found in gardens.
Chalky Soil: Also called lime-rich soils containing calcium carbonate it sits over limestone or chalk bedrock and is very alkaline, drains freely.
The best way to tell what type of soil you have is by touching it and rolling it in your hands.
Sandy soil has a gritty element – you can feel sand grains within it, and it falls through your fingers. It cannot be rolled to make a sausage shape. If it is not a coarse sand and perhaps a sandy loam it may stick together better
Clay soil has a smearing quality, and is sticky when wet. It is easily rolled into a long thin sausage and can be smoothed to a shiny finish by rubbing with a finger. If is it not a heavy clay it won’t get quite as shiny and be as easy to make a sausage
Pure silt soils are rare, especially in gardens. They have a slightly soapy, slippery texture, and do not clump easily
If soil froths when placed in a jar of vinegar, then it contains free calcium carbonate (chalk) or limestone and is lime rich.
Another important aspect of soil type, is the pH (acidity or alkalinity). This will also affect the type of plants you can grow and how you manage your soil. (Royal Horticultural Society)
Humus is an integral part of almost all good growing soil. So, just what is humus? Soils are influenced, modified, and supplemented by living organisms. Plants and animals aid in the development of a soil through the addition of organic matter. Fungi and bacteria decompose this organic matter into a semi-soluble chemical substance known as humus. Larger soil organisms, like earthworms, beetles, and termites, vertically redistribute this humus within the mineral matter found beneath the surface of a soil.
Humus is the biochemical substance that makes the upper layers of soil become dark. It is colored dark brown to black. Humus is difficult to see in isolation because it binds with larger mineral and organic particles. Humus provides soil with a number of very important benefits:
It enhances a soil’s ability to hold and store moisture.
It reduces the eluviation of soluble nutrients from the soil profile.
It is the primary source of carbon and nitrogen required by plants for their nutrition.
It improves soil structure which is necessary for plant growth. (phoslab.com)
1. Put 1 cm of soil into a test tube
2. Add 1 cm of barium sulphate to the test tube (this attaches to fine particles and makes them sink leaving a clear layer above it)
3. Add enough distilled water to bring the level half way to the top of the test tube
4. Add two pipettes full of indicator solution
5. Seal the test tube with a rubber bung and shake well (make sure that the contents are mixed thoroughly)
6. Allow the test tube to stand until the soil has settled out leaving a coloured solution
7. Hold the tube next to the colour chart and decide which pH colour it most closely matches.
8. Dispose of the soil in the bin.
Alternatively hand held digital pH probe can quick and simple to use both in the filed or in the lab.
container of water (keep this constant between experiments – 4 litres is enough)
30 cm ruler
metal / plastic tube (to be the ‘infitration tube’)
stopwatch
block of wood
mallet
at least 2 people – one to pour in water, the other to operate the stopwatch and take readings
Bang the infiltration tube into the ground until it forms a seal (using the wood and mallet to bang it in evenly and avoid affecting the results by stamping on the area of land being tested).
One person fills the infiltration tube to a standardised level (e.g. 15cm). The other starts the stopwatch, and then record the water level every 30 seconds. To maintain water pressure, person 1 should top up the infiltration tube if their water level falls below a certain point (e.g. 10cm). Person 2 should make a note of when this is done, so that it can be taken it into account when they are calculating their infiltration rate.
Find the mass of a heat resistant crucible.
Half fill the crucible with soil from the soil sample and then weigh it again.
Place the crucible in an oven at a temperature just above the boiling point of water (ideally around 105°C) until it is dry.
You can tell when it is completely dry by weighing the crucible and soil, returning it to the oven for 10 minutes and weighing again and so on, until there is no change in weight after 10 minutes. Don’t be tempted to turn the oven up to make the drying take place more quickly. You will only begin to burn off the humus in the soil and won’t then be able to find out either the weight or humus content accurately. Now record the weight of the crucible and dry soil. Find the difference between the dried soil and the fresh soil, and use this to calculate the % moisture content of the fresh soil.
The most effective way to burn off the humus is to use a furnace that is capable of reaching a temperature of 550°C. If this is not available, a Bunsen burner can be used instead.
If using a furnace, place the crucible and dry soil into a furnace at 550°C for 15-30 minutes, until all the humus has been burnt off.
Or if using a Bunsen burner. Using a tripod and gauze sheet, heat the soil sample in a crucible above a full-flame Bunsen burner for 30 minutes to 2 hours, until all the humus has been burnt off.
Record the weight of the crucible and soil and calculate the percentage of humus in the soil. The mass of dry soil, rather than the mass of wet soil, is used to calculate the percentage humus content. Using dry soil mass allows you to compare soil samples taken on different days.