There are very few such silos remaining, they became outdated technology and as they tended to be in the farmyard the space they stood on was valuable.
Historic England describes them:
SILAGE CLAMP AND TOWER
Airtight containers for the storage of freshly cut grass and
its conversion into silage were first developed in the 1880s,
after its initial use elsewhere in Europe. Silage afforded the
opportunity to cut and store grass for bulk fodder without
the risk of poor weather or storage conditions spoiling the
hay or root crop.
• Silage clamp – An airtight container for the storage of
freshly cut grass and its conversion into silage. Silage
clamps were brick or concrete walled structures, in which
the silage would be placed and then covered over.
• Silage tower – A tower for the airtight storage of freshly
cut grass and its conversion into silage. A silage tower
is recognisable as a tall structure. Tower silos were
introduced from the United States in 1901, but were not
in general use until after the Second World War.
• There is at least one example of a silage clamp in mass
concrete of the 1880s, otherwise they are modest
• Intact examples of silage towers of 1940 or earlier,
using concrete or displaying a degree of architectural
elaboration, are rare.
(There is a silage clamp at the nearby buildings constructed of reused concrete railway sleepers which is the replacement for the silo.)
The grass was loaded in to the top of the silo by either an elevator as this colour wartime photo shows or chopped and blown up a tube. It was consolidated to make it anaerobic, usually by being trampled down as the level rose. Molasses or acid was added to create the right conditions for butyric fermentation to pickle the grass.
Click photos to embiggen
The Stonehenge silo looks to be 1940s or even earlier and is a rare example and worthy of interest and preservation