Tramlines are parallel lines in crops that allow farmers to drive through their fields to fertilise and spray accurately without causing damage to surrounding plants. The lines of a tramline are usually about 30 cm wide and 2 metres apart while the distance between tramlines can vary from 12 metres to 30 metres.

Tramlines became widespread in their use in the agricultural revolution of the 1950s and 60s. Tramlines are of vital importance in the modern farming environment because they prevent overlapping applications of fertiliser and pesticide and because they allow spot or selective treatments to be carried out accurately. Nowadays tramlines can be seen throughout most of the western world and are often inaccurately present in films about the past, watch Gladiator carefully next time!

Tramlines originate at the time of drilling the crop and are incorporated by the drill which has the ability to switch off the seed delivery to some of the coulters (the red tubes that place the seed in the soil) thereby leaving strips through the field with no crop. Because tramlines are incorporated by the drill, they are always relative to the growing crop and therefore an accurate guide through it.

In some instances tramlines will need to be followed before the crop has emerged. In these circumstances the drill lowers a set of discs into the soil immediately behind the drill. These leave a mark which can be followed. The set of discs (marked by the arrow) are lifted out of the soil when a tramline is no longer being incorporated.

In this image tramlines have been followed by a tractor even though there is no crop present. Farmers sometimes have to drive through their fields before a crop emerges to apply fertiliser or a herbicide. Herbicides used like this are known as pre-emergence and work by controlling very small weeds as they emerge through the soil. Pre-emergence herbicides are not effective against established weeds and have to be applied to the bare soil very soon after drilling.

This tramline is seen in a crop of wheat in May. Note the bare soil in the centre of each line and the way the crop is beginning to arch over to make use of the light in an area without competition. Tramlines do potentially create a loss of yield, however this can be minimsed where the distances between the tramlines are as great as possible. In the UK tramlines are normally centred at between 18 and 24 metres.

In the summer months most farmers will change their tractor wheels to narrower "row crop" wheels. These are better suited for travelling through the crop as they do not damage the plants nearest the tramline itself. However, these wheels are no use in the winter months as they are unable to support a tractor in wet conditions. Row crop wheels tend to increase the compaction of the ground in a tramline because they exert more pressure on the soil. Compaction can lead to poor drainage and waterlogging which disadvantages the nearby crop. To get round this farmers may "subsoil" the tramline.

The benefits of a tramline: the end of the sprayer boom is able to accurately follow the crop and therefore prevent application of the spray onto the grass margin that runs alongside. Without a tramline the operator would inevitably weave in and out as he attempted to stear a straight line through a field. This would result in some areas being oversprayed and some undersprayed, both wasteful and inefficient.

Tramlines are not just used by man in the management of crops. Many kinds of birds use them to land in the crop before walking in search of food or to a nest and foxes and deer will regularly follow them as they travel across the countryside. .

Tramlines persist until harvest and are periodically used by combine drivers as they seek to straighten a wayward cut!

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