Soil Health Basics
Find out what your soil is made of with your fingers, a jar, and a cup of water. Whatever you build or grow later, and anything you sell, has to work in somebody's soil.
Module sheet 1 of 5
- You make
- A jar test of your own soil, with every layer measured
- You measure
- How much of it is sand, silt, and clay, and how fast water drains through it
- Bring
- A clear straight-sided jar with a lid, about two cups of soil, water, a drop of dish soap, and a ruler
- Toward a sale
- A seedling or a tool that fails in a buyer's soil won't sell twice. Knowing soil tells you who your product works for.
What soil is made of, and why water cares
Soil is mineral grains, organic matter, air, and water, plus the bacteria, fungi, and worms that break dead plants down. The mix decides how fast water soaks in, how long it stays, and how far a root can reach.
The later modules lean on this. A drip rate that suits a sandy bed floods a clay one, and a seedling tool that works in potting mix can jam in garden soil.
- Texture. Sand, silt, and clay particles, and how their ratio sets drainage and how hard the ground is to dig.
- Organic matter. What compost and mulch add, and why soil with more of it holds water longer.
- Structure. How grains clump into crumbs, and how walking on wet beds crushes them.
- Life in the soil. The bacteria, fungi, and worms that turn dead plant matter into food plants can use.
- Smell and color. Quick checks: dark and earthy is usually healthy, and a sour, rotten smell points to waterlogged soil with no air in it.
- Soil as a tank. How much water a soil holds once it has drained, which sets how often you need to water.
Five tests, one patch of ground
Run them in order on the same soil. Each one ends with something to write down, and by the last one you have a soil profile you can show a mentor or a partner garden.
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Feel test
Wet a pinch of soil and rub it between finger and thumb. Gritty means sand, smooth like flour means silt, sticky means clay. Then squeeze it out between your fingers into a ribbon: the longer it gets before it breaks, the more clay.
Write downGritty, smooth, or sticky, and the ribbon's length in centimetres
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Jar test
Fill a jar a third of the way with soil, add water to near the top and a drop of dish soap, shake for three minutes, and set it down. Sand settles in about a minute, silt over a few hours, and clay can take a day or two.
Write downThe height of each layer, and each one as a share of the total
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Drainage race
Cut three plastic bottles in half, set a coffee filter in each neck, and fill them with sand, garden soil, and clay soil. Pour the same cup of water into each and time it.
Write downSeconds until the first drip and until it stops, and how much water came through
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Compost check
Mix compost into one pot of compacted soil and leave a second pot plain. Water both the same way for a week.
Write downDays until each surface dries out, and whether it crumbles or stays a clod when you squeeze it
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Root path
Sow a bean against the side of a clear cup, push a couple of pebbles into the soil, and mark where the root tips are every day.
Write downRoot length each day, and what the roots did when they reached a pebble
The numbers behind the tests
Each one says where it comes from, so you can check it yourself.
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Sand grains are 0.05 to 2 mm across, silt 0.002 to 0.05 mm, and clay smaller than 0.002 mm.
USDA particle-size classes. A grain sinks through water at a speed that grows with the square of its size (Stokes' law), which is why the jar sorts itself into sand, then silt, then clay.
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A teaspoon of healthy soil can hold more living things than there are people on Earth.
A figure from USDA Natural Resources Conservation Service soil-health material. Counts per gram vary a lot from soil to soil, so read it as a sense of scale.
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The world's soils hold more carbon than all its plants and its air put together.
Roughly 1,500 billion tonnes in the top metre of soil, against about 870 in the atmosphere and 450 to 650 in vegetation (IPCC Sixth Assessment Report).
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Water spreads sideways in clay and drops straight down in sand.
Small pores pull water sideways by capillary action; big pores let gravity win. It is why module 2 spaces emitters closer together in sandy beds.
By the end, you can
- Name your soil's texture by feel and check it with a jar
- Explain why the same watering suits one bed and drowns another
- Tell whether a bed needs compost, mulch, or fewer feet on it
- Pick a starting drip rate in module 2 from what you measured here
Take it into your project
If your project goes in the ground, test the soil it will meet before you build anything: your own bed, a partner garden's, or a customer's. Bring the results to a workshop or a field pilot.
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