The fact that land which frequently bears a crop of clover becomes rapidly unfit to bear further crops of this plant is a very old observation in all countries where clover is grown. In England, Arthur Young (1804) called attention to it and to the fact that farmers were accustomed to call this unfitness “clover sickness”. The cause of this soil condition has been a matter of careful study since early in the nineteenth century, and some of the most interesting observations on the subject were made by Lawes & Gilbert (1860) in the years preceding 1860. They showed that the lack of capacity to grow clover did not seem to be connected with any deficiency in the principal specific plant foods in the soil, and the only contrary evidence was the fact that when a rich garden soil was substituted for the ordinary field soil, it was possible to grow clover for a much longer period without failure (Gilbert, 1871). The final conclusion of Lawes & Gilbert as to the so-called clover sickness was that the only means of ensuring a good crop of red clover is to allow some years to elapse before repeating the crop on the same land.