 Once dried, they could be burnt, and the ashes used as fertiliser.This practice, known as paring and burning, was used widely in the Fens, and was advocated by Walter Blith in his book "The English Improver Improved", published in 1652.He suggested that it should be used on the lowest levels of fen land which had been 'long drowned', and recorded details of the practical application of the process to an area of in the Bedford Level.