Silage is a form of conserved grass (or other crop) that is made by farmers during the summer months when the grass supply is plentiful and not required for grazing. Silage is fed to cattle and sheep during winter months and is made by preserving the grass under naturally produced acidic conditions which effectively pickle the crop. Silage is quite moist and usually preferred by livestock to hay as it is more palatable and of higher food value. It often forms the bulk of the livestock diet for six months of the year through the winter months.

Grass silage is usually produced by stock farmers two or three times a year, however it is the first cut of grass in late May that is the most important. Growth at this time of year is vigorous and the grass is rich in energy as it produces leaf rather than going to seed. Grass crops for silage are fertilised to increase production and can look very much like a conventional arable crop. The image illustrates grass ready for silage making and is typical of the many hundreds of thousands of hectares that are conserved each year.

The first process in the production of silage is mowing. Here a mower is cutting a grass crop that is about 60cm tall. The mower width will vary according to local field sizes but all mowers cut the grass into lines known as a swath which can easly be picked up by a forage harvester (a machine that picks up the cut grass).

The image illustrates grass swath being cut from the outside of the field inwards. It is important for the operator that mows the grass to ensure that the mower is raised by the hydraulic lift arms of the tractor as soon as it reaches the end of the standing crop of grass. This prevents the mower from disturbing rows that have been previously cut.

The forage harvester illustrated is offset from the tractor and this allows it to pick up grass that has not been driven on by the tractor. Forage harvesters have a series of rotating tines that lift the grass from the ground before feeding it into a chopper. The chopper cuts the grass to a predetermined length before blowing the cut material into a trailer for tansport to the storage area.

There are two main arrangements for collecting the grass from the forager harvester. Either a trailer can be towed by the forage harvester itself or a tractor and trailer will drive alongside to collect grass on the move. This image illustrates a trailer being towed and filled. This system is favoured by smaller farms that do not have a large workforce to draw on.

A seperate tractor and trailer are being used to collect the chopped grass. This method is the choice of contractors because the grass is constantly being picked up and no time is lost in dropping off and rehitching to another trailer. Many farmers use contractors to make silage because it is often a cheaper option. Owning large items of machinery can be uneconomic if they are only used for a few days a year.

In the farm yard the grass is deposited in a heap (the clamp) and pushed up by a handler into a large pile. The siting of the clamp is important because it must be easily accessible during winter months when the stock need feeding. In addition silage clamps cannot be situated close to water courses as the effluent that emerges from a clamp could suffocate fish.

The process of building the clamp involves the removal of as much air from the grass as possible and to do this the loader or a tractor will repeatedly drive over the clamp. The compression of the grass will eventually reach the point where the clamp becomes fairly firm to walk on sheeting the clamp can begin.

Most silage clamps are covered with black plastic sheets. Special attention has to be made to ensure that air cannot get into the clamp, either from the top or around the edges. If air does get into the clamp the grass will not ensile properly and the resultant silage will be of poor nutritional quality and of low palatability. At the conclusion of sheeting hundreds of tyres will be used to hold the sheet firm and to maintain the airtight finish until the time of use in the winter.

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