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Enter your soil test targets to size compost, lime, and sulfur needs for this bed.
Soil amendment planning has two jobs at once: correcting chemistry such as pH and rebuilding the organic material that influences structure, drainage, and moisture storage. A bed can look productive while still tying up nutrients or drying too quickly, so modest shifts in pH or organic matter often have practical consequences out of proportion to the numbers themselves.
This calculator turns those goals into quantities you can actually move. Give it bed area, working depth, soil texture, current and target pH, and current and target organic matter, and it translates the gap into compost volume, lime or elemental sulfur weight, optional gypsum, packaging counts, and a material budget in either imperial or metric units.
A realistic example shows the value of that translation. A 200 square foot bed worked to 6 inches with loam, current pH 5.8, target pH 6.5, current organic matter 3.2%, and target organic matter 5.5% returns about 0.35 cubic yards of compost and about 7 pounds of agricultural lime at 90% CCE.
The tool is aimed at spaces where logistics matter as much as chemistry: raised beds, kitchen gardens, hoop-house rows, and other small plots where wheelbarrow loads, bag sizes, and total carrying weight affect the work.
The result is still a planning model rather than a laboratory prescription. Texture factors, focus mode, and product assays create a consistent estimate, but they do not replace a current soil test or a check of the product labels you are about to spread.
The best first pass is simple: enter a recent soil test, keep Amendment focus on Balanced (soil test), and leave the advanced product settings at their defaults unless you already know your bag weights, compost density, and assay values.
Keep chemistry separate from logistics. Area, depth, texture, pH, organic matter, focus, lime CCE, sulfur assay, and the gypsum toggle shape the recommendation itself. Bag sizes, wheelbarrow capacity, compost density, and bag costs only change the way that recommendation is packed, carried, and priced. If the pH shift or OM gain badges look wrong, fix those assumptions before you compare bag counts in Application Plan.
The calculator combines a simple geometry model with a texture-weighted amendment model. Bed area and incorporation depth are converted into a working soil volume. From there, the tool tracks two separate improvement targets: a pH gap and an organic matter gap. Compost is driven by the organic matter gap, while lime or sulfur is driven by the pH gap.
Texture matters because the package uses different factors for sandy loam, loam, clay loam, and heavy clay. Lime increases as soils get heavier, sulfur also increases with heavier textures, and gypsum is treated as an optional texture-based add-on. Product quality matters too: lime demand is scaled by calcium carbonate equivalent, and sulfur demand is scaled by elemental sulfur percentage.
Several advanced fields are deliberately logistical rather than agronomic. Bulk density affects the displayed soil mass only. Compost density affects compost weight, while bag sizes and bag costs affect package counts and budget totals. That keeps hauling and shopping choices from silently changing the underlying amendment quantities.
The core equations convert bed dimensions and soil test gaps into material quantities. The pH and organic matter goals remain separate all the way through the calculation.
| Symbol | Meaning in this tool | Unit | Source |
|---|---|---|---|
| A | Bed area converted to square feet | ft² | Bed area |
| d | Target incorporation depth in inches | in | Target depth |
| ΔOM | Target organic matter minus current organic matter, never below zero | percentage points | Current OM and Target OM |
| ΔpH | Target pH minus current pH | pH units | Current pH and Target pH |
| F | Texture-specific amendment factor | lb per 100 ft² basis | Soil texture |
| CCE | Calcium carbonate equivalent of the lime product | % | Lime CCE |
| %S | Elemental sulfur percentage in the product | % | Sulfur assay |
The shipped texture table changes lime, sulfur, and gypsum demand directly. The Amendment focus control then nudges those quantities: Organic matter first reduces lime and sulfur by 15%, while Raise pH priority or Lower pH priority increases the relevant pH material by 10%.
| Soil texture | Lime factor | Sulfur factor | Gypsum factor |
|---|---|---|---|
| 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 |
Gypsum is handled as an optional structure-oriented material. When the switch is on, the tool adds a gypsum quantity based on texture and area, but the pH shift badge does not change. In this package, gypsum is a separate calcium and structure input, not the agent responsible for pH correction.
| Control group | Effect in this tool |
|---|---|
| Bed area, Target depth, Soil texture, pH targets, OM targets | Change the base compost, lime, sulfur, and gypsum quantities. |
| Lime CCE and Sulfur assay | Adjust the lime or sulfur amount to reflect product strength. |
| Amendment focus | Biases lime or sulfur slightly toward pH or away from it. |
| Bulk density | Changes displayed soil mass only. |
| Compost density, bag sizes, wheelbarrow capacity | Change weight, bag counts, and hauling estimates, not the base recommendation. |
| Bag costs and Notes seed | Change budget totals and the advisory wording only. |
The main bounds come from the package itself: area and depth must be positive, depth is clamped to 2 to 12 inches, current pH to 4.0 to 8.5, target pH to 5.0 to 7.5, current organic matter to 0.5% to 12%, target organic matter to 1.0% to 15%, lime CCE to 60% to 110%, and sulfur assay to 70% to 99%. If area or depth is invalid, the results tabs stay hidden and the red error box explains why.
A solid plan starts with believable soil test inputs and only then moves into packaging and budget details.
A good finished run gives you believable chemistry targets, realistic hauling numbers, and a plan that still makes sense when checked against the labels on the actual products you buy.
The key outputs are compost volume, lime or sulfur weight, and the summary badges for OM gain and pH shift. The rest of the package helps you act on those numbers by translating them into bags, wheelbarrow trips, chart bars, and a staged application sequence.
The false-confidence trap is assuming the model predicts the exact post-application soil test you will see later. It does not. Use the result as a structured estimate, then verify it against a current lab report, the assay printed on the product, and a later soil test.
Use 200 sq ft, 6 inches, loam, current pH 5.8, target pH 6.5, current OM 3.2%, target OM 5.5%, balanced focus, 90% lime CCE, and default compost logistics. The tool returns about 0.35 cu yd of compost, about 4 wheelbarrow loads at 3 cu ft each, about 345 lb of compost at the default compost density, and about 7.0 lb of lime.
In Amendment Metrics the dominant quantity is compost, while Application Plan lists compost first and lime second. That is a classic case where hauling work outweighs chemical weight.
Set 100 sq ft, 6 inches, sandy loam, current pH 7.2, target pH 6.4, current OM 4.5%, target OM 4.5%, and Lower pH priority. Because the organic matter gap is zero, compost stays at zero. Sulfur becomes the main adjustment, landing near 0.8 lb after the 10% focus increase.
That result is useful because it separates the two goals cleanly: Amendment Metrics shows sulfur but no compost, and Amendment Weights reduces to a single meaningful bar. The plan is about pH, not bulk organic inputs.
Enter Bed area as 0 while leaving other fields untouched. The tool clears the result tables, shows the red error message that area must be a positive number, and keeps Amendment Metrics, Application Plan, and Amendment Weights from rendering.
The corrective path is to restore a valid area and rerun the plan. Once the error is cleared, the result tabs return automatically and the summary line recalculates from the same chemistry settings.
No. The package assumes you already have reasonable current and target values for pH and organic matter. It is strongest as a planning layer on top of a soil test, not as a substitute for one.
Because the tool treats gypsum as an optional structure-oriented calcium input. It adds gypsum weight when the switch is on, but the pH shift badge continues to reflect lime or sulfur logic only.
Because compost weight is often much larger than pH-adjustment materials, especially after the selected Compost density converts volume into pounds or kilograms.
No. They change bag counts and budget totals only. Base compost volume and lime, sulfur, or gypsum quantities come from the soil and product inputs, not the package sizes.
No. This package runs locally in the browser and does not include a server-side processing path for your soil inputs.