The process mentioned in the first passage is the removal and replacement of topsoil. The topsoil is being removed and replaced because European agricultural processes have resulted in a depletion of soil nutrients. This in turn has led to the heavy fertilizing of soil which can cause problem weeds to grow when the land is uncultivated.
As we know that heavy fertilizing is a part of the problem, it makes sense that any soil brought in to replace the heavily fertilized topsoil would not also contain large amounts of fertilizer.
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