Soil Amendment Calculator

Soil Amendment Plan

Total amendment weight

{{ summaryAreaDisplay }} Depth {{ depthDisplay }} Compost {{ compostDisplay }} Loads {{ compostWheelbarrows }} Lime {{ limeDisplay }} Sulfur {{ sulfurDisplay }} Gypsum {{ gypsumDisplay }} Weight {{ totalWeightDisplay }} Cost {{ totalCostDisplay }} OM gain {{ organicMatterDeltaDisplay }} pH shift {{ phChangeDisplay }}

Measurement system:

Bed area:

Target depth:

Soil texture:

Current pH:

Target pH:

Current OM:

Target OM:

Amendment focus:

Bulk density:

g/cm³

Lime CCE:

Sulfur assay:

Include gypsum:

Wheelbarrow capacity:

Compost density:

Compost bag size:

Compost bag cost:

Lime bag size:

Lime bag cost:

Sulfur bag size:

Sulfur bag cost:

Gypsum bag size:

Gypsum bag cost:

Notes seed:

Metric	Value	Copy
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No metrics available.

Step	Amount	Focus	Notes	Copy
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No application steps required.

Chart compares amendment weights. Elemental sulfur is shown even if spread across multiple applications.

Enter your soil test targets to size compost, lime, and sulfur needs for this bed.

Tags: Education , Gardening , Productivity

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Soil amendments are materials added to change soil chemistry and structure so crops can root well and grow steadily. A soil amendment calculator helps turn a lab report into practical amounts you can spread with confidence. The aim is clear guidance that aligns with your bed size and the results you want.

Soil pH and organic matter are the two anchors because pH shapes nutrient availability and organic matter supports water holding and biology. You describe the bed area and working depth, choose a texture that matches your report, then give current and target values for pH and organic matter. Select imperial or metric once and the calculator converts every field and result automatically, packaging compost volume with wheelbarrow loads, bag counts, and amendment weights, plus an optional gypsum suggestion you can price immediately.

For example, a 200 square foot (≈18.6 m²) bed set to 6 inches (≈15 cm) with loam and a pH change from 5.8 to 6.5 returns about 0.35 cubic yards (≈0.27 m³) of finished compost, roughly four loads at 3 cu ft each (≈85 L), and about 7 pounds (≈3.2 kg) of agricultural lime—one standard 40 lb (≈18 kg) bag. If you add bag prices, the plan surfaces a quick material budget before you head to the supplier.

Field conditions vary and soil biology works on its own time, so retest after improvements and avoid chasing day to day swings. Measure area carefully, and lean on the measurement toggle to keep units consistent while you select the closest texture from your lab sheet. Use the Advanced panel to align wheelbarrow capacity, bag sizes, and pricing with what you can actually buy; if a result looks extreme, check for typos or mismatched units before you spread.

Technical Details:

The calculator operates on two observable quantities from a soil report: soil pH and organic matter by weight. It treats your bed as a uniform layer at a chosen depth and estimates how much compost shifts organic matter and how much lime or elemental sulfur shifts pH in the intended direction.

From area and depth it derives soil volume and an estimated soil mass using a bulk density you can set. Organic matter change is modeled as a percentage point gap to close, which maps to compost depth and volume. pH change is modeled as a difference that maps to material pounds per 100 ft², scaled by texture factors and product assays.

Results are interpretable directly: compost is listed in cubic yards or cubic metres alongside wheelbarrow loads and bag counts aligned with the volume you specify; pH agents are in pounds or kilograms with matching bag totals and optional cost rollups; gypsum stays optional because it supplies calcium without changing pH. A focus setting lets you lean toward organic matter or toward pH, slightly scaling the respective materials.

Comparability assumes even incorporation to the target depth and consistent compost quality between applications. Values are sized for home and market beds, not bulk acreage, and are intended for year over year alignment rather than exact short‑term corrections.

\begin{array}{lll} A {(ft}_{2} & = & A {(input}_{)} \times k, k = {1 or 10.7639 \\ V {(ft}_{3} & = & A {(ft}_{2} \times \frac{d}{12} \\ ρ {(lb/ft}_{3} & = & ρ {(g/cm}_{3} \times 62.42796 \\ M (lb) & = & V \times ρ \\ Δ OM & = & max (0, OM (target) - OM (current)) \\ Y (cu yd) & = & \frac{A}{1000} \times \frac{d}{6} \times Δ OM \times 0.75 \\ L (loads) & = & ceil (Y \times 27 / 3) \\ Δ pH & = & pH (target) - pH (current) \\ lime (lb) & = & \frac{A}{100} \times Δ pH \times F (lime, texture) \times \frac{100}{CCE} (\mo>Δ pH > 0) \\ sulfur (lb) & = & \frac{A}{100} \times | Δ pH | \times F (sulfur, texture) \times \frac{90}{%S} (\mo>Δ pH < 0) \\ gypsum (lb) & = & \frac{A}{100} \times F (gypsum, texture) \end{array}

Symbols and units used in formulas
Symbol	Meaning	Unit/Datatype	Source
A	Bed surface area	ft² or m²	Input
d	Incorporation depth	inches	Input
V	Soil volume to amend	ft³	Derived
ρ	Dry bulk density	g/cm³ → lb/ft³	Input → Derived
M	Estimated soil mass	lb	Derived
OM	Organic matter by weight	%	Input
ΔOM	Target minus current OM	percentage points	Derived
Y	Finished compost volume	cubic yards	Derived
L	Wheelbarrow loads	3 ft³ per load	Derived
ΔpH	Target minus current pH	pH units	Derived
CCE	Calcium carbonate equivalent	%	Input
%S	Elemental sulfur assay	%	Input
F(lime, texture)	Lime factor by texture	lb / 100 ft² / pH	Constant
F(sulfur, texture)	Sulfur factor by texture	lb / 100 ft² / pH	Constant
F(gypsum, texture)	Gypsum factor by texture	lb / 100 ft²	Constant

Texture factors used in calculations
Soil texture	F(lime)	F(sulfur)	F(gypsum)
Sandy loam	3.5	0.9	2.0
Loam	4.5	1.2	2.8
Clay loam	6.0	1.5	3.6
Heavy clay	7.5	1.8	4.5

Texture factors, depth and assay handling reflect the shipped logic and UI controls.

Worked example. Inputs: 200 ft², 6 in, Loam, pH 5.8 → 6.5, OM 3.2% → 5.5%, bulk density 1.1 g/cm³, CCE 90%, sulfur 90%. Compost Y ≈ 0.35 cu yd (4 loads, 4 bags @ 1 cu ft). Lime ≈ 7.0 lb (≈1 bag). Sulfur 0 lb. Interpretation: pH rises toward the target while organic matter increases modestly over one incorporation; enter bag pricing to see the matching material budget.

Variables & parameters

Key parameters and their roles
Parameter	Meaning	Unit/Datatype	Typical Range	Sensitivity	Notes
Area	Bed surface size	ft² or m²	10–20000 ft²	Linear	Meters converted at 10.7639.
Depth	Incorporation layer	inches	2–12	Linear	Usually top 6 inches.
Bulk density	Dry soil density	g/cm³	0.7–1.6	Linear	Maps to lb/ft³ via 62.42796.
CCE	Lime neutralizing power	%	60–110	Inverse	Lower CCE requires more lime.
%S	Elemental sulfur assay	%	70–99	Inverse	Lower assay requires more material.
Focus	Priority setting	enum	Balanced / OM / pH up / pH down	Scaler	±10–15% scaling to match intent.

Validation & bounds

Inputs, ranges, steps, and messages
Field	Type	Min	Max	Step/Pattern	Error Text	Placeholder
Bed area	number	10	20000	1	Area must be a positive number.	200
Area unit	select	—	—	sq ft \| sq m	—	—
Target depth	number	2	12	0.5	—	6
Soil texture	select	—	—	4 options	—	—
Current pH	number	4.0	8.5	0.1	—	5.8
Target pH	number	5.0	7.5	0.1	—	6.5
Current OM	number	0.5	12	0.1	—	3.2
Target OM	number	1	15	0.1	—	5.5
Bulk density	number	0.7	1.6	0.05	—	1.1
Lime CCE	number	60	110	1	—	90
Sulfur assay	number	70	99	1	—	90
Include gypsum	boolean	—	—	switch	—	—
Notes seed	text	—	32 chars	string	—	e.g. soil-lab-2025

Units, precision & rounding

Decimal separator is a dot. No thousands separators are interpreted.
Displays round to 0–2 decimals as shown in the metrics table, using standard nearest rounding.
Wheelbarrow loads default to 3 ft³ (≈85 L) per load and adjust with the capacity field. Compost weight in charts uses an internal density approximation.

Algorithmic notes

Clamp all numeric inputs to defined ranges before computation.
Compute soil volume and mass from area, depth, and density.
Convert OM gap to compost volume; compute loads.
Map pH gap to lime or sulfur using texture factors and product assays.
Apply focus scaling: organic matter first reduces pH agents by 15%; pH priority increases the relevant agent by 10%.
Optionally add gypsum by texture; it does not alter pH.
Split elemental sulfur into two passes when the per‑100 ft² rate exceeds five passes equivalent in the plan notes.

I/O formats & encoding

Input and output families
Input	Accepted Families	Output	Encoding/Precision	Rounding
Numbers	Integer or decimal with dot	Metrics table	Text, 0–2 decimals	Nearest at set precision
Selections	Texture, units, focus	Application plan	Text steps	—
Toggle	Include gypsum	Chart	Bar series	1 decimal
Seed	Alphanumeric text	JSON export	Pretty printed	Exact values

Randomness, seeds & reproducibility

Companion advice notes are chosen with a deterministic generator seeded by your parameters and optional note seed. The selection is repeatable for the same seed and inputs and never affects the material calculations.

Networking & storage behavior

All calculations run in the browser. No data is transmitted to a server during use.
A charting script is loaded from a public content network to render the bar chart.
Copy, download, and document export actions create client‑side files or clipboard text only.

Assumptions & limitations

Heads‑up Compost quality varies; the model assumes finished, stable compost.
Heads‑up pH change is estimated; true buffering depends on carbonates and clay content.
Texture choice is a coarse category; choose the closest match from your report.
Mixing is assumed uniform to the set depth; spot incorporation reduces effect.
CCE and sulfur assay are taken at face value; verify product labels.
Wheelbarrow capacity defaults to 3 ft³ (≈85 L) for planning convenience but can be tuned to match your equipment.
Gypsum improves structure without changing pH; sodium issues are not modeled.
Focus scaling is modest and does not override large pH gaps.
Very small beds can be hard to measure; round cautiously.
Retesting is recommended after 12–18 months to avoid overshooting.

Edge cases & error sources

Zero or negative area is rejected.
Values outside allowed ranges are clamped before math.
Comma decimal separators are not accepted; use a dot.
Extremely high OM targets may be impractical in one season.
Very shallow depths produce small, hard‑to‑spread quantities.
Blocking clipboard permissions prevents copying metrics or JSON.
Blocked third‑party scripts disable the chart view.
Manual rounding may differ slightly from displayed values.
Entering mismatched units leads to apparent over or under application.
Old lab results can mislead planning if the bed has changed.
Seed changes affect advice text only, not the plan itself.
Browser extensions that alter pages can disrupt formatting.

Privacy & compliance

Processing is client‑only and intended for general gardening guidance. No personal data or identifiers are required or stored. Outputs support planning and are not professional agronomy advice.

Interface elements, actions, and ranges reflect the packaged markup and logic, including CSV/JSON handling and document export controls.

Step‑by‑Step Guide:

Size amendments from your soil test and bed layout to produce a concise application plan.

Select the Measurement system (Imperial or Metric) to set all units.
Enter Bed area; the unit next to the field updates with your selection.
Set Target depth for incorporation.
Choose Soil texture closest to your report.
Fill in Current pH and Target pH.
Fill in Current OM and Target OM.
Pick a Focus that matches your goal.
Open advanced options to tune density, CCE, sulfur assay, wheelbarrow capacity, packaging, pricing, or include gypsum.
Optionally add a Notes seed for repeatable tips.
Review metrics, the plan, and the chart; copy or download what you need.

Example: 200 ft² (≈18.6 m²), 6 in (≈15 cm), Loam, pH 5.8 → 6.5, OM 3.2% → 5.5% ⇒ ~0.35 cu yd (≈0.27 m³) compost (4 loads, 4 bags) and ~7.0 lb (≈3.2 kg) lime (~1 bag) with cost totals when prices are supplied.

You now have amounts you can spread and a short note for follow‑up.

FAQ:

Is my data stored?

No. Calculations run in the browser and exports are created locally. Nothing is sent to a server.

Client‑only processing.

How accurate are the amounts?

They are planning estimates based on texture factors and product assays. Soil buffering, compost variability, and mixing quality can shift real‑world outcomes.

Retest in 12–18 months.

Which units can I enter?

Pick Imperial or Metric at the top and the form updates: area uses sq ft or m², depth flips between inches and centimetres, and wheelbarrow and bag fields follow suit. Percentages use a dot for decimals.

No thousands separators.

Can I use it without internet?

Yes, after the page loads. The chart requires a script that may not be available offline; the calculations still work.

Chart availability may vary.

What does “borderline” change mean?

When the pH or OM gap is very small, amounts round to near zero. In that case maintain current practices and retest before adjusting.

Avoid overshooting.

How do I repeat the same advice note?

Enter a notes seed and keep other inputs the same. The generator uses the seed and your parameters to repeat the same companion tip.

Seed affects notes only.

Why is gypsum “not recommended”?

Gypsum is optional and appears when you switch it on. It adds calcium without changing pH and can help heavy textures or sodium issues.

Toggle in advanced options.

Can I export the plan?

Yes. You can copy metrics or JSON and create a document for record keeping. Exports are generated on the device.

No uploads.

Troubleshooting:

No results shown: ensure area is positive and complete all fields.
Weird units: confirm the area unit matches your entry.
Chart missing: allow the chart script and reload the page.
Copy fails: grant clipboard permission or use the download option.
DOCX not created: allow file downloads and try again.
Values look extreme: recheck pH and OM targets and texture selection.
Gypsum absent: turn on the gypsum option in advanced settings.
Decimals ignored: use a dot instead of a comma.

Blocking issue: Area set to zero or negative prevents any calculation. Enter a positive number.

Glossary:

Soil pH: Acidity or alkalinity level that affects nutrient availability.
Organic matter (OM): Decomposed plant and animal residues measured as percent by weight.
Bulk density: Dry soil mass per volume used to estimate bed mass.
Calcium carbonate equivalent (CCE): Neutralizing strength of lime products compared with pure CaCO₃.
Assay (%S): Elemental sulfur percentage on the product label.
Texture factor: Per‑100 ft² material rate linked to the chosen texture.
Wheelbarrow load: Planning unit equal to 3 ft³ of compost.
Gypsum: Calcium sulfate amendment that does not change pH.