The Garden 4:307 (October 11, 1873)

CHARCOAL AS A FERTILISER

I WANT some treatise on the virtue, chemical properties, and proper application of charcoal as applied to land. My soil is light sandy loam, and I can procure 100 loads of charcoal dust at little or no expense, except drawing one and a half miles.—THOMAS ROGERS.

Answer by Professor S. W. Johnson in New York Tribune:—There is good proof that charcoal has an excellent effect on light land deficient in attractiveness for moisture, especially in dry seasons. This is due to its great porosity and absorbent power for vapour of water. As is well known, charcoal takes up a large amount of water when kept in a cool damp celler—becomes, in fact, so wet that it is difficult to set it on fire. On a soil already hygroscopic from presence of clay or humus, or in wet seasons, it has, of course, no good effect from this quality. On a heavy clay, which is unfavourable to vegetation because of its compactness and slow penetrability by water, charcoal powder, like any non-adhesive dust, separates the clay particles, prevents their cohesion where it intervenes, and thus tends to make the soil more open, more friable, and more early, promotes drainage, and sets in train a long series of changes for the better. Charcoal strewn on the surface of light-coloured soil, so as to blacken it, enables the soil to become warmed under the sun's rays more rapidly and more highly than would be the case otherwise. This fact may partly account for the good effect reported of it in cold climates. Charcoal has been reputed to act as a fertiliser because of its absorbent power for ammonia. It does, in fact, condense in its pores fifty to one hundred times its bulk of ammonia gas when its pores are perfectly free from air moisture and all other gases, and when the ammonia gee is also unmixed with other gases. But these conditions never exist in nature, and the fact is that charcoal exposed to the air never contains or absorbs any important amount of ammonia, and does not fertilise by acting as a means of collecting and storing this gas. Charcoal is a powerful oxidising agent, and this quality may not unlikely come into play usefully when it is mixed with the soil. Dr. Stenhouse was the first to show that the offensive gases which escape from putrefying animal matters are deodorised and destroyed when made to pass a layer of charcoal dust, and that the result is brought about by the oxygen gas condensed in the pores of the charcoal. A dead rat, nicely buried in a cigar box so as to be surrounded at all points by an inch of charcoal powder, decays to bone and fur without manifesting any odour of putrefaction, so that it might stand on a parlour table and not reveal its contents to the most sensitive nostrils. The gaseous products of decay under such conditions are carbonic acid, ammonia, and water, or the same that would result were the ordinary effluvium of putrefying flesh burned in a furnace. The soil often, if not always, contains nitrogen in combination with some form of humus, which is inert, or at least not immediately available as fool to crops. Charcoal, we should anticipate, would hasten or set up oxidation of these matters, and might liberate a portion of this inactive nitrogen, in the form of ammonia or of nitrates, and thus enhance the fertility of the soil. This is, however, but a speculation, a bit of theory, and while probable enough to warrant investigation, must not be accepted as a fact until it has been proved to be such. As a direct fertiliser, i.e., by virtue of anything it can yield of its own substance to crops, charcoal cannot be regarded as of much value. It contains, of course, if it has not been washed by water, the ash elements of the wood from which it has been made, and when applied in large quantity the potash, lime, &c., which it carries upon the land may easily produce a striking effect upon poor soil. This kind of effect cannot last more than a single season, and on a soil in fairly good condition would commonly make no show. From these considerations we conclude that, while charcoal (unless, as may often happen, it is mixed with a good deal of wood-ashes) is not of much value as a fertilizer directly, it is a valuable amendment to soils which are dry from their coarse, sandy texture, or are wet from consisting of too tenacious clay.