Soil Testing

Part of Fertilizers & Soil Amendments

Testing soil composition, texture, and nutrient status using hands-on methods available without modern laboratories.

Why This Matters

Soil is not just dirt — it’s a complex mixture of minerals, organic matter, water, air, and living organisms, and its composition determines what you can grow and how well. Two fields a hundred meters apart can have completely different soil types: one sandy and drought-prone, the other clay-heavy and waterlogged. Treating both the same wastes effort and amendments.

Modern soil labs analyze samples with spectroscopy, chromatography, and precise chemical tests. Without these, you might assume soil testing is impossible. But farmers tested soil for centuries before laboratories existed, using observation, feel, smell, and simple field tests that reveal the critical properties: texture, drainage, organic matter content, pH, and biological activity.

These low-tech tests won’t give you a number for parts-per-million of zinc, but they will tell you whether your soil is sand or clay, whether it drains too fast or too slow, whether it’s acidic or alkaline, and whether it has enough organic matter to support healthy crops. That information drives 90% of soil management decisions. The remaining 10% — micronutrient levels — you diagnose from plant symptoms after planting.

The Jar Test: Soil Texture Analysis

This is the most informative single test you can perform. It reveals the proportions of sand, silt, and clay in your soil — the three components that define texture and determine drainage, workability, and nutrient-holding capacity.

Procedure

1. Collect a representative soil sample from 15-20 cm depth
2. Remove stones, roots, and debris
3. Fill a straight-sided clear glass jar one-third full of soil
4. Add water to near the top, leaving 2 cm of air space
5. Add one teaspoon of salt (helps clay particles separate and settle)
6. Seal the jar and shake vigorously for 3-5 minutes
7. Set on a level surface and do not disturb

Reading the Results

The particles settle in order of size:

Time	Layer	Material
Within 1 minute	Bottom layer	Sand (coarsest particles)
After 2-4 hours	Middle layer	Silt (medium particles)
After 24-48 hours	Top layer	Clay (finest particles)

After 48 hours, carefully mark the boundaries between layers on the outside of the jar. Measure each layer’s thickness and calculate percentages.

Interpreting Texture

Sand %	Silt %	Clay %	Texture Class	Agricultural Properties
>85	<10	<10	Sand	Drains fast, holds few nutrients, warms quickly
40-65	20-40	10-25	Loam	Ideal — balanced drainage, nutrients, workability
20-40	40-60	15-25	Silt loam	Good fertility, can compact and crust
<30	<30	>40	Clay	Holds water and nutrients, hard to work, slow to warm

The Ideal

Loam — roughly equal parts sand, silt, and clay — is the ideal agricultural soil. If your jar shows heavy clay or sand dominance, amendments (organic matter for clay, organic matter plus clay additions for sand) can improve texture over years.

The Feel Test: Quick Texture Assessment

When you need a quick answer in the field without waiting 48 hours:

1. Take a walnut-sized lump of moist soil
2. Roll it between your palms, trying to form a ribbon

Result	Soil Type
Falls apart immediately, feels gritty	Sandy
Forms a short ribbon (2-3 cm) before breaking	Loam
Forms a medium ribbon (3-5 cm), slightly sticky	Clay loam
Forms a long, smooth ribbon (>5 cm), very sticky	Clay
Feels silky and smooth, makes a short ribbon	Silty

Additional touch tests:

• Grittiness when rubbed between thumb and finger: Sand content
• Smoothness/silkiness: Silt content
• Stickiness when wet: Clay content
• Staining on hands: Organic matter content (darker stains = more organic matter)

Drainage Test (Percolation)

Drainage is as important as texture for crop selection and management.

Procedure

1. Dig a hole 30 cm deep and 30 cm wide
2. Fill the hole completely with water
3. Let it drain completely (this saturates the surrounding soil)
4. Fill the hole with water again
5. Measure how long it takes to drain this second time

Interpretation

Drain Time	Rating	Implications
Under 10 minutes	Excessive	Nutrients leach quickly; needs organic matter
10-30 minutes	Good	Ideal for most crops
30-60 minutes	Moderate	Acceptable; avoid flood-sensitive crops
1-4 hours	Slow	Risk of root rot; needs drainage improvement
Over 4 hours	Very poor	Raised beds or drainage ditches needed

Organic Matter Assessment

Organic matter is the life of the soil — it feeds microorganisms, holds nutrients, retains water, and builds soil structure. Assessing its level guides composting decisions.

Color Test

Organic matter darkens soil. Compare your soil to a reference:

Color (when moist)	Estimated Organic Matter	Assessment
Pale gray/tan/white	<1%	Very low — needs heavy composting
Light brown	1-2%	Low — regular compost additions needed
Medium brown	2-4%	Moderate — maintenance composting
Dark brown	4-6%	Good — soil is biologically active
Very dark/nearly black	>6%	Excellent — maintain current practices

The Burn Test

A more precise organic matter estimate:

1. Dry a soil sample thoroughly in the sun or near a fire
2. Weigh the sample (or fill a small container to a mark)
3. Place in a very hot fire (or a kiln if available) for 30 minutes — hot enough to glow red
4. Let cool completely
5. Weigh again (or note the level in the container)

The weight lost is primarily organic matter that burned away. A 5% weight loss means approximately 5% organic matter.

Biological Activity Tests

The Earthworm Count

Earthworm abundance is one of the best single indicators of soil health.

1. Dig a 30 x 30 x 30 cm block of moist soil
2. Sort through it carefully, counting all earthworms
3. Interpret results:

Count	Assessment
0-3	Poor soil biology — add organic matter, check pH
4-7	Fair — continue building organic matter
8-12	Good — soil biology is healthy
13+	Excellent — thriving soil ecosystem

The Smell Test

Healthy soil has a distinctive pleasant, earthy smell — caused by geosmin, a compound produced by beneficial soil bacteria (actinomycetes). This smell indicates active, healthy soil biology.

Smell	Assessment
Pleasant earthy scent	Healthy, biologically active soil
No particular smell	Low biological activity — needs organic matter
Sour/vinegar-like	Waterlogged, anaerobic conditions — improve drainage
Rotten egg smell	Severely anaerobic — drainage emergency
Ammonia smell	Recent heavy manure application, or compacted manure layer

The Cotton Strip Test

A simple way to measure decomposition rate (biological activity):

1. Bury a strip of untreated cotton fabric (an old cotton shirt works) 15 cm deep
2. Mark the location
3. Dig it up after 6-8 weeks
4. Assess how much the fabric has decomposed

Condition	Biological Activity
Intact, barely changed	Very low — soil biology is weak
Partially frayed, some holes	Moderate — building but not yet thriving
Heavily degraded, falls apart	Good — active decomposer community
Nearly gone, just threads remain	Excellent — very high biological activity

Compaction Test

Compacted soil restricts root growth, reduces water infiltration, and limits air exchange. Testing for compaction is simple.

Wire Probe Method

1. Take a stiff wire or thin metal rod (3-4 mm diameter)
2. Push it into moist soil (not dry or waterlogged — both give misleading results)
3. Note the depth at which resistance suddenly increases

Easy Penetration Depth	Assessment
>30 cm	No compaction problem
15-30 cm	Moderate compaction — consider deep tillage
<15 cm	Severe compaction — hardpan likely present

Repeat at multiple locations. If you consistently hit resistance at 15-20 cm, you likely have a plow pan (compacted layer created by repeated tillage at the same depth). Breaking this layer requires deep cultivation with a subsoiler or digging fork.

Nutrient Indicator Tests

The Acid-Base Test

See pH Testing for detailed methods. As a quick summary: add vinegar to soil (fizzing = alkaline) and baking soda to soil (fizzing = acidic).

Nitrogen Quick Test (The Grain Soak Method)

A traditional farmer’s test for nitrogen availability:

1. Soak a handful of wheat or barley grains in water for 12 hours
2. Place the soaked grains on a moist soil sample, 1 cm deep
3. Cover with a damp cloth
4. Check germination and growth after 5-7 days

Seedling Appearance	Estimated Nitrogen
Tall, deep green seedlings	Good nitrogen
Medium height, light green	Moderate nitrogen
Short, yellowish seedlings	Low nitrogen — needs amendment

This works because seedling growth in the first week depends heavily on soil nitrogen availability.

Phosphorus Indicator (The Bean Test)

Bean seedlings show phosphorus deficiency rapidly:

1. Plant 5-10 bean seeds in a small pot of your soil
2. Plant 5-10 beans in a pot of soil mixed with bone meal
3. Compare growth after 3 weeks

If both pots grow equally, phosphorus is adequate. If the bone meal pot dramatically outperforms, your soil needs phosphorus.

Creating a Soil Profile

Digging a Test Pit

A soil profile pit reveals layers (horizons) that influence root growth and drainage.

1. Dig a hole 60-90 cm deep with one vertical wall
2. Smooth the vertical face with a flat tool
3. Observe and record the layers:

Horizon	Typical Depth	What to Look For
O (organic)	0-5 cm	Decomposing leaf litter, plant debris
A (topsoil)	5-30 cm	Dark, crumbly, root-rich — the productive layer
B (subsoil)	30-60 cm	Lighter color, denser, fewer roots
C (parent material)	60+ cm	Rock fragments, unweathered material

Key observations:

• Topsoil depth — Deeper is better. Less than 15 cm of topsoil limits crop performance.
• Color changes — Abrupt color transitions may indicate compaction layers or drainage problems.
• Mottling — Orange and gray spots indicate seasonal waterlogging (water table fluctuation).
• Root penetration — Note the deepest roots you find. If roots stop abruptly at a layer boundary, that layer is a barrier.

Putting It All Together

The Complete Field Assessment

When evaluating a new growing area, perform these tests in order:

1. Feel test — Immediate texture assessment (30 seconds)
2. Smell test — Biological activity indicator (10 seconds)
3. Wire probe — Compaction check (2 minutes per spot)
4. Drainage test — Percolation assessment (30-60 minutes)
5. Jar test — Detailed texture analysis (set up in 5 minutes, read next day)
6. pH test — Vinegar/baking soda or cabbage indicator (10 minutes)
7. Earthworm count — Biological activity quantification (15 minutes)
8. Soil profile — Subsurface investigation (30 minutes of digging)
9. Color assessment — Organic matter estimate (immediate after digging)

Record all results for each growing area. This baseline tells you:

• What to grow where (sandy areas for root crops, clay areas for brassicas)
• What amendments are needed (lime for acid soil, compost for low organic matter, drainage for clay)
• What problems to expect (compaction, waterlogging, nutrient deficiency)

Seasonal Retesting

Test at least annually:

• pH (to track liming effectiveness)
• Earthworm count (soil health trend)
• Organic matter color (improvement over time)

Test every 3-5 years:

• Full jar test (texture changes very slowly)
• Soil profile (horizons develop over decades)

The goal is not a single perfect test but a pattern of observation over years. Each test builds your understanding of your land. After three or four seasons of testing and observing crop performance, you’ll know your soil better than any laboratory report could tell you.