Note 2880 — BOOK XVII. THE NATURAL HISTORY OF THE CULTIVATED TREES.
John Bostock translation
Marl does not begin to fertilize till several years after it has been laid down; hence, it is generally recommended to marl the land a little at a time, and often. If the ground is fully marled, it requires to be marled afresh in about eight or ten years, and not fifty, as Pliny says.