Extra sheep are being drafted in to the Queen's Norfolk estate to boost the fertility of the soil.

Prince Charles, who oversees the management of Sandringham, is behind the plan.

The estate is currently home to around 3,000 sheep. A Kensington Palace spokesman said: 'There's been an increase in the number of sheep but it's more to do with soil health than commercial reasons.'

The animals' droppings will provide a natural means to make the estate's sandy soil more fertile. It was recorded in the Domesday Book as Sant Dersingham - the sandy part of Dersingham - which was later shortened.

Eleanor Phipps, spokesman for the National Sheep Association, said: 'Once you put sheep bank onto land, they will fertilise it very quickly.

'A lot of big estates do put sheep on land because they can re-fertilise the grass and make it better land to run other animals on.' Sandringham is also home to a 300-strong herd of rare red poll beef cattle, while thousands of acres are used for growing arable crops.

Sheep have been farmed since Roman times and became hugely important for their skins, wool and meat in Medieval times.

More recently, the animals have become part of farmers' crop rotations, with land which has been in production put out to grass to recover its fertility with the help of the sheep.

Sandringham also grows wheat, barley, peas, sugar beet, beans, oats, parsnips and maize, along with apples and soft fruit.

Prince Charles has taken over the running of the estate since the retirement of his father, the Duke of Edinburgh.

The Duke had run Sandringham since the Queen inherited it after the death of her father, King George VI, in 1952.

The Prince is well-known for his belief in organic farming. He is patron of both the Soil Association and the Rare Breeds Survival Trust, which says he plays 'an active role' in supporting its work.

Conservation has been central to the philosophy of the estate for half a century.

More than 5,000 trees and several miles of hedges are planted each year, while sympathetic farming practices encourage wildlife, like the geese which share its rolling pastures with the sheep.