Having read about Soil Properties, why not get out and assess (some of) your own? The following experiments are easy to do and will really help you understand your soil!
This is a fundamental test everyone should do. You’ll need to buy a pH kit but these are readily available from many garden centres on and offline, cost around $20 or less, and are very easy to use. Make sure you get one intended for soil though! (Some are designed for hydroponic systems, ponds, or pools.)
Determine the proportions of sand, silt, clay and organic matter in your soil by feel! A soil with a high proportion of sand will feel gritty, a soil with a high proportion of silt will feel silky, and a soil with a high proportion of clay will feel sticky and can easily be rolled into a ribbon.
The method outlined below is routinely done ‘in the field’ when there is no access to more accurate equipment. It can take some practice to perfect, so don’t be afraid to do this several times to be sure of your result:
1. Take a handful of soil and remove any stones, sticks, leaves or bark. Don’t worry about any really tiny pieces of organic matter you may see, you just want to remove the ‘ obvious’ pieces that are easy to see and pick out.
2. Knead this sample between your fingers and thumb. You want a moisture content such that the soil just fails to stick to your fingers. If too dry, wet the soil slightly with a small amount of water and keep kneading. (An eye-dropper or squirt bottle is handy.) Keep kneading until you reach both this moisture content and you can no longer detect a change in consistency. Be sure to break down all lumps of soil so as not to confuse these for sand grains
3. Can you see any visible sand? Or did you hear and feel any when working your sample?
4. Squeeze the sample hard to see if a ball or cast forms. Does this shape hold or does it fall apart?
5. Squeeze this shape between your thumb and forefinger with a sliding motion. Does a self-supporting ribbon form, and if so, what is its length?
Here’s how to interpret your results:
a. Doesn’t stick together and can’t be formed into a ball or cast. Single sand grains stick to fingers — sand
b. Forms a cast that just bears handling and which falls apart easily. Forms a very short 6 mm ribbon that breaks easily — loamy sand
c. Forms a fragile cast that is sticky when wet, with many sand grains sticking together. Forms a ribbon 5-15 mm long— clayey sand
d. Forms a cast that just bears handling, and in which individual sand grains can be seen and felt. Forms a ribbon 15-25 mm long — sandy loam
e. As for sandy loams, but individual sand grains can’t be seen, though can be heard and felt. Also forms a ribbon 15-25 mm long — fine sandy loam
f. Holds a cast that feels spongy. No obvious sandiness or silkiness, but may feel greasy if a lot of organic matter is present. Forms a ribbon about 25 mm long — loam
g. Holds a cast but will crumble. Feels very smooth and silky. Forms a ribbon 25 mm long — silty loam
h. Forms a very firm cast in which sand grains can be felt. Forms a ribbon 25-40 mm long — sandy clay loam
i. Forms a very firm cast with a spongy feel and which is pliable when squeezed between thumb and forefinger and smooth to manipulate. Forms a ribbon 40-50 mm long — clay loam
j. Forms a pliable cast in which sand grains can still be seen, felt or heard. Forms a ribbon 50-75 mm long — sandy clay
k. Forms a very pliable cast with slight resistance to shearing between thumb and forefinger. Forms a ribbon 50-75 mm long — light clay
l. Forms a smooth, pliable cast which handles like plasticine. Can be formed into rods that don’t break, but with some resistance to ribbon-forming. Forms a ribbon at least 75 mm long — medium clay
m. Forms a smooth, pliable cast which handles like stiff plasticine. Can be formed into rods that don’t break and without resistance to ribbon-forming. Forms a ribbon at least 75 mm long — heavy clay
This is a very quick and handy test to know that can be performed on the spot and with access to water. Sometimes, though, it can produce misleading results, as soils that feel alike can differ quite a bit from each other in their proportions of sand, silt and clay. If you wish to know the actual proportions of these components you can have a particle size analysis done at a laboratory that determines soil particle sizes with calibrated sieves and a mechanical shaker, or you can do a good-enough one yourself at home with a glass jar and some water!
Determine the proportions of sand, silt, clay and organic matter in your soil visually, and compare with what you felt above!
1. Collect about two cups of soil and remove any large sticks, leaves, stones or bark
2. Place one cup of this “cleaned” soil into a straight-sided 500 mL glass jar with a tight-fitting lid
3. Add water to a level of about 2cm from the top of the jar
4. Place the lid tightly on the jar and shake vigorously for 3-5 mins
5. Place on a table or even higher at eye level if possible — you want to be able to observe and measure the jar later without disturbing the contents, and having the jar at a height beforehand makes this easier and more comfortable. Allow the contents to settle undisturbed for a couple of days or even a couple of weeks. The more clayey your soil the longer it will take these lighter particles to settle. The water layer may still be discoloured after this time owing to any dissolved organic matter present
Assuming your sample has all four components, small rocks (if present) and sand particles are the largest and heaviest, and will settle on the bottom. The next layer will be silt, followed by clay. If your soil is mostly clay you’ll likely only see clumps of clay on the bottom.
Above these solid layers will be the water. Any discolouration is due to rotted organic material that has dissolved in this layer. Any non rotted organic material will be floating on top of this water layer. Here’s my garden soil:
(I stuck a ruler onto the jar above with a loop of sticky tape for this photo, and lined the ruler up to be flush with the very bottom of the sand layer, not the very bottom of the jar which was about 2.5 mm thick glass. The ruler appears to be lower than this owing to camera position and parallax.)
This is where choosing a jar with straight sides becomes important! Ignore the water level and measure the total height of the combined soil fractions, as well as the height of each layer. Divide the height of each layer into the total soil height and multiply by 100 to express as a percentage.
For me, the soil was 39 mm high. Sand particles formed a 27 mm layer. Silt formed a 9 mm layer, and clay formed a 3 mm layer. Thus this soil is 69% sand, 23% silt and 8% clay. (Check that your numbers add up to 100 so as to pick up any calculation errors.)
(If you’re struggling to see the silt layer in the above photo, it isn’t you! It’s definitely visible when viewed at eye level in direct sun.) I had to keep picking up the jar to confirm with my own eyes it really truly was there too!)
Reading these results from the Soil Texture Triangle below tells me I have a sandy loam. To read your results, find the sand % value along the bottom of the triangle and follow the diagonal that slopes up to the left. For silt, find the % value along the right of the triangle and follow the diagonal that slopes down to the left. For clay, find the % value on the left of the triangle and follow the line that goes straight across to the right. As each fraction adds up to 100%, the three lines will converge at a single point, and the section that point is in corresponds to your soil type.
Now that you know a bit more about your soil up close and personal (or, perhaps, mine!), we will examine soil structures in more detail over the next few weeks. Soil structure has a big influence on plant growth, and is well worth understanding.
This week’s soil experiments conclude next week with a wrap-up discussion as to what your soil results mean.
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