This section is from the book "Commercial Gardening Vol1", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
Where a rational system of cultivation is not practised, recourse is had to steaming or burning the soil. Many growers of Ferns, for example, place the soil in receptacles of some kind, and have it burned in the furnaces before sowing spores upon it. The idea is that the excessive heat kills all the "bad" or unfriendly bacteria and leaves the good or friendly ones intact. It has been stated that bacteria are killed outright at 195° F., and that they cease to work, and become comatose or unconscious, at 132° F. Consequently, when soil is heated to 200° or 300° F. it follows that the bacteria must be killed right out, and the soil reverts to a more or less sterile condition. Because, in addition to killing the bacteria, if the heat is too intense all organic material will be driven off also, leaving only the mineral substances of the soil. This result can be achieved without burning, simply by crushing pieces of brick or mortar, and sowing the spores upon them, as many growers do.
A CITY OF GLASSHOUSES AT WALTHAM CROSS, NEAR LONDON.
Photos, by Chas. L.. Clarke.
Steaming the soil would have rather a different effect from burning. The bacteria would be killed, but the organic material would remain; but whether it would retain all its nitrates and other foods or not experiment only could prove.
Comparing the methods of growers who "sterilize" their soils with those who do not, the latter produce at least as good crops as the former, if not better, and without incurring further expense. Generally speaking, if soils before use are well exposed to the action of the weather, and are not afterwards overdosed with strong manures, they will continue to yield excellent results.