Silage Fermentation & Quality, pH and Loss Forecast

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.

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.

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.

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.

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.

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 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.

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.

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.

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.

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.

Yes. The whole calculation runs locally in your browser. Nothing you enter is uploaded or stored anywhere — close the tab and it is gone.