The precise conditions which make it most advantageous, are not positively determined yet. Wood ashes contain a large amount of carbonate of potassa, with also the sulphate and silicate of that alkali. Peat ashes vary in different regions, but always are found useful as manure. A hundred pounds to the acre of grass or young corn, have been reported to produce a beneficial effect. In localities far inland, common salt, chloride of sodium, is indispensable to the soil, although a small amount of it will suffice.
Animal manures contain it.