Silage Fermentation & Quality, pH and Loss Forecast
Predicts fermentability
From dry matter, sugar and buffering, get the Weissbach fermentability coefficient, the chop and additive advice, the predicted stable pH and dry-matter loss from pack density — with a clostridial spoilage flag.
Crop & clamp
Next: act before you ensile: wilt drier to lift the fermentability coefficient and push pack density above 240 kg DM/m³, chop to fine (8–12 mm) + acid/inoculant, and apply the needed acid or inoculant to drive the pH down past 4.5 quickly.
| Fermentability (FC) | Additive | Chop |
|---|---|---|
| Easy to ensile (≥45) | none | normal (15–25 mm) |
| Moderate (35–45) | helpful | shorter (10–18 mm) |
| Difficult to ensile (<35) | needed | fine (8–12 mm) + acid/inoculant |
| Pack density (kg DM/m³) | Base DM loss |
|---|---|
| ≥ 280 | 8% |
| 240–280 | 11% |
| 200–240 | 15% |
| 160–200 | 20% |
| < 160 | 28% |
FC = DM% + 8×(WSC/buffering) per Weissbach; density-loss bands per Holmes & Muck (Wisconsin). Planning estimates — confirm with a forage lab and on-clamp density checks.
Silage fermentation — key facts
- FC formula
- DM% + 8 × (WSC ÷ buffering)
- Easy to ensile
- FC ≥ 45 (no additive)
- Moderate / difficult
- 35–45 helpful / < 35 needed
- Target density
- ≥ 240 kg DM/m³
- Loss at ≥ 280
- ≈ 8% DM
- Loss below 160
- ≈ 28% DM
- Stable pH (good)
- ≈ 3.8–4.2
- Clostridial danger
- pH 4.5–5.5
- Source
- Weissbach; Holmes & Muck (Wisconsin)
- Privacy
- Runs in your browser; nothing uploaded
Crop fermentability reference
Typical water-soluble carbohydrate and buffering capacity for common forages, with how readily each ensiles. Pick a crop in the tool to load these, or enter your own forage-lab values.
| Crop | WSC (% DM) | Buffering (g/kg) | Ensiling note |
|---|---|---|---|
| Maize (whole-crop) | 18 | 25 | High sugar, low buffering — ensiles easily. |
| Perennial ryegrass | 14 | 40 | Good sugar if wilted; moderate buffering. |
| Whole-crop cereal | 12 | 30 | Drier, moderate sugar — usually easy. |
| Lucerne / clover | 7 | 65 | Low sugar, high buffering — hard to ensile. |
| Grass-legume mix | 10 | 52 | Intermediate; additive often pays. |
| Forage sorghum | 15 | 28 | Sugary, ensiles well if not too wet. |
Fermentability bands & pack-density loss
| FC band | Additive | Chop |
|---|---|---|
| Easy to ensile (≥ 45) | none | normal (15–25 mm) |
| Moderate (35–45) | helpful | shorter (10–18 mm) |
| Difficult to ensile (< 35) | needed | fine (8–12 mm) + acid/inoculant |
| Pack density (kg DM/m³) | Base DM loss (180 d) |
|---|---|
| Excellent (≥280) | 8% |
| Good (240–280) | 11% |
| Fair (200–240) | 15% |
| Poor (160–200) | 20% |
| Very poor (<160) | 28% |
FC bands per Weissbach; density-loss base values per Holmes & Muck (Wisconsin) silage density guidelines, for a 180-day store with well-managed feed-out.
Decide before you clamp, not at feed-out
Silage quality is largely decided in the hours around ensiling: how dry the crop is, how much sugar it carries, how hard it resists acidification, and how tightly it is packed. By the time you open the clamp and smell a butyric fermentation, the decisions that mattered have already been made. The Weissbach fermentability coefficient lets you forecast the outcome up front — combining dry matter, sugar and buffering into one number that says whether the crop will ensile easily, needs a shorter chop, or needs an additive to be safe.
This tool turns that forecast into a clamp plan: it shows the pH curve falling from fresh crop toward a stable value, flags it red if it stalls in the clostridial danger band, and predicts the dry-matter loss and recovered tonnage from your pack density. The silo cross-section deepens in colour as you raise density and the air voids shrink, making the single most controllable factor — compaction — visible. Pair it with the Silage Loss and Annual Fodder Requirement tools to budget the winter feed your clamp will actually deliver.
How to use the calculator
- 1Pick the crop. Choose your forage to load typical sugar and buffering, or enter your own forage-lab figures.
- 2Enter dry matter and density. Add the crop dry-matter percent and your target clamp pack density in kg DM/m³.
- 3Set storage and tonnage. Enter the storage days and the fresh tonnes you will ensile.
- 4Read the forecast. See the fermentability coefficient, additive and chop advice, predicted pH and dry-matter loss.
- 5Act before you ensile. If the pH stalls in the clostridial band, wilt drier, chop finer, pack denser or add an additive.
Frequently Asked Questions
What is the Weissbach fermentability coefficient?+
The fermentability coefficient (FC) is a single number that predicts how easily a crop will ferment into good silage. Weissbach defined it as FC = dry-matter % + 8 × (water-soluble carbohydrate ÷ buffering capacity). An FC of 45 or more means the crop ensiles easily; 35–45 is moderate, where an additive helps; below 35 is difficult and an additive is needed. It combines the three things that decide fermentation — dryness, sugar and how much the crop resists acidification.
Why does sugar and buffering capacity matter so much?+
Silage is preserved by lactic-acid bacteria fermenting the crop's sugars into acid, which drops the pH until spoilage organisms can no longer grow. Water-soluble carbohydrate is the fuel for that fermentation; buffering capacity is how strongly the crop resists the pH fall. A sugary, low-buffering crop like maize acidifies fast and easily; a low-sugar, high-buffering crop like lucerne resists, which is why it is hard to ensile without help.
What pack density should I aim for?+
Aim for at least 240 kg of dry matter per cubic metre. Below that, too much air is trapped in the clamp and aerobic losses climb steeply; the calculator's density-loss table shows base dry-matter loss rising from about 8% at 280+ kg DM/m³ to 28% below 160. Higher density squeezes out air, lowers porosity and protects the silage — it is the single most controllable factor in feed-out loss.
How is dry-matter loss predicted?+
The tool reads a base loss from the pack-density band (Holmes/Muck Wisconsin data for a 180-day store), then adds extra loss for storage beyond 180 days and a penalty when the crop is hard to ferment. So a well-packed, easy-to-ferment crop fed out promptly loses little, while a loose clamp of a difficult crop stored a long time loses far more. The recovered silage tonnage falls directly out of that loss.
What is the clostridial danger band and why is it flagged?+
Clostridia are spoilage bacteria that cause butyric fermentation — foul-smelling, protein-degrading silage with effluent. They are inhibited only once pH falls below about 4.5; between roughly 4.5 and 5.5 they thrive. If the predicted stable pH stalls in that 4.5–5.5 band, the tool flags it red, because it means the crop is not acidifying enough to be safe and you need to wilt drier, chop finer or add an acid/inoculant.
Does a wetter crop really ferment worse?+
Wetter crops (lower dry matter) ensile less reliably: there is more water to dilute the sugar, effluent carries nutrients away, and the higher buffering of lush wet forage resists the pH drop. That is why the fermentability coefficient rises with dry matter — wilting to a sensible target before clamping is one of the cheapest ways to improve silage quality and cut effluent.
When do I actually need a silage additive?+
When the fermentability coefficient is below about 45. Between 35 and 45 a homofermentative inoculant or acid additive is helpful and usually pays; below 35 — wet lucerne or clover, for example — it is needed to drive a safe fermentation. Above 45 the crop ferments well on its own and an additive mainly buys insurance or aerobic stability. The tool states which case you are in.
What chop length should I use?+
Easier-fermenting crops can take a normal 15–25 mm chop. Moderate crops do better with a shorter 10–18 mm chop, which releases more sugar and packs tighter. Difficult crops want a fine 8–12 mm chop plus an additive, because tight packing and fast sugar release are needed to acidify a stubborn forage. The calculator recommends the chop that matches your crop's fermentability.
How much silage will I recover from my fresh crop?+
The tool takes your fresh tonnage, converts it to dry matter at your dry-matter percent, applies the predicted dry-matter loss, then converts the surviving dry matter back to silage tonnes. So 100 tonnes of 30% DM crop at an 11% loss recovers roughly 89 tonnes of silage; the same crop in a loose clamp at 28% loss recovers far less. It puts a tonnage on the cost of poor clamp management.
Is the fermentability coefficient the same as silage pH?+
No, but they are linked. The fermentability coefficient predicts before ensiling how easily the crop will ferment; pH is the result you measure afterwards. A high FC tends to give a low, safe stable pH; a low FC risks a high, unsafe pH that stalls in the clostridial band. The tool models both — the FC up front and the expected pH curve — so you can act before clamping rather than discover a problem at feed-out.
How accurate are these figures?+
The fermentability coefficient and density-loss relationships come from peer-reviewed forage-conservation literature (Weissbach; Holmes and Muck), so they are sound planning figures. Actual results depend on filling speed, sealing, weather and feed-out management, and on accurate inputs — ideally a forage-lab water-soluble-carbohydrate and buffering analysis. Treat the output as a well-grounded estimate to guide decisions, not a guarantee.
Does this run in my browser, and is my data private?+
Yes. The whole calculation runs locally in your browser. Nothing you enter is uploaded or stored anywhere — close the tab and it is gone.