Mineral fertilizer

Simple lime, although an important constituent of plants, is rarely suitable as an application to them in its pure state. Carbonate of lime (represented by chalk, &c.) is a natural ingredient in very many soils.

The sulphate of lime (gypsum, plaster of Paris) is often used for fertilizing purposes. It is less easily decomposed than the carbonate. The precise conditions which make it most advantageous, are not positively determined yet. Phosphate of lime is a very important constituent of plants; and, as it exists also in the bones of animals, a double relation follows: namely, that it should be abundant in soil on which plants are raised for food of men and animals; and, on the other hand, that animal bones contribute it to the soil when they decay upon it.

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. Kelp, or the ashes of sea-weeds, are often employed in the same way; they contain soda in considerable amount. Nitrate of potassa (nitre, or saltpetre) is said to quicken vegetable action when added to the soil, and to give the leaves a deeper green. 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. An excess of salt will render land barren; as was well known to the ancients.

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