Charcoal

Wood and bone charcoal used as an early practice of improving heavier soils by mixing it into the soil. It must not be regarded as a fertiliser, but simply as a purifying absorbent, which tends to aerate, purify and sweeten the soil, it improves the drainage, makes the playing surface firm and clean, fines down turf, and eliminates moss . (Source: Beale, E. (1924), Lawns for Sports, p190). The meaning of fines down turf is that of making downland turf be composed of more finer grass species.