to ensure it keeps cooking. Then, when it reaches the dark, slightly cooler state of the chip at the end of the row, he spreads it over his green-manure crops, twice every seven years, and leaves the worms to pull it into the earth. This, apart from seed, is the only substance applied to the fields that comes from outside the farm. Altogether, he lays down a depth of just seven millimetres of chip during the rotation: an average of one millimetre per year.
