Density reduces weathering loss and raises the risk of heating, and the two effects move in opposite directions at the same time. The trade is real and it is not symmetrical.
Denser bales cut storage loss and raise the heat risk
window HAY WINDOWwritten 2026-08-12responsible Windrow Field Manual (a named masthead, not a person)
[['Density up', 'Falls: less surface per tonne', 'Rises: the core sheds heat more slowly'], ['Density down', 'Rises: more surface, more weather', 'Falls: the bale cools faster'], ['Density up, moisture down', 'Falls on both counts', 'Falls — this is the only free move']]
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Why the trade is not symmetrical
Weathering loss is roughly proportional to exposed surface, so it falls steadily as density rises. Heat risk is not proportional to anything so simple: it is a threshold effect, and it rises slowly and then very fast as the bale crosses the moisture the core can tolerate. That asymmetry is why the two effects cannot be traded off with a single number.
| Density | Storage loss, outdoor | Safe baling moisture | Net position |
|---|---|---|---|
| Low | High | Wide band | Cheap to make, expensive to store |
| Medium | Moderate | Moderate band | The working compromise |
| High | Low | Narrow band | Expensive to get wrong |
The move that is free
Denser bales at lower moisture improve both measures at once. There is no trade in that direction, and the reason it is not the standard practice is that lower moisture means waiting, and waiting means weather risk. The trade is therefore between density and time, not between density and storage.
The manual holds that the decision should be made on the storage the bales are going into, not on the bale. Bales going into a barn for six months can be made at the top of the band. Bales going into an outdoor stack cannot, and the density that would help the stack is the density that makes the moisture dangerous.
What the manual would measure next
- Core temperature series for the same crop baled at two densities.
- Weathered dry-matter loss for the same two densities, weighed rather than estimated.
- The moisture at which each density starts to climb past 55 °C.
Where the numbers come from
- S1Large Round Bale Storage Costs (Focus on Forage), University of Wisconsin-Madisonsupports the storage-cost framing used when density is being justified
- S2Forage Storage, Michigan State University Extensionsupports the forage storage practice the density choice sits inside
- S3Moisture Content and the Hay Drying Curve, Field Crop News, Ontario Ministry of Agriculture, Food and Agribusinesssupports the drying curve that sets how low the moisture can go
One link, one document. No home pages, no search results, no bare domains.
Put this page down Put this page down when you know which storage the bales are going into. That decides the density.