Reversible ploughs or ploughing in lands.

The two main types of plough.

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A reversible plough can be turned over by the tractor's hydraulics at the end of the furrow and the next pass made against the previous strip. The ploughman drives backwards and forwards across the field until all is done. If the field is flat he will turn the soil one way one year and the opposite way the next. If there is a slope he turns the soil uphill every year to counter the natural downhill slippage.

A non reversible plough can only turn the soil one way. If the ploughman were to run back alongside the previous furrow the soil would pile up in the middle. Instead the field is divided into lands. A land is an arbitrary area around which the ploughman drives in an elongated spiral. All the soil is turned the same way and there is only one slight ridge in the middle where the soil was turned together. As each land is finished and the next started there is a shallow trench left between the adjacent lands. Each year a good ploughman checks the position of the previous years lands and positions his new lands to cancel out the effect. Alternatively he will start to plough from the outside one year and from the middle out the next. The result is the same.

What is sillion? A farmer's explanation of Gerard Manley Hopkins' most famous poem.