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INORGANIC MANURES.

Sawdust is therefore a most excellent substance to mixwith the excrement of animals, and other strong animalmanures.

434. The number of inorganic substances employedas manures is very great, and tbeir use is naturally muchdependent on the nature of the soil. In many cases greatbenefit is derived from mixing soils: either mixing aportion of the subsoil with the surface-soil (383), orby adding to the soil, earth brought from a distance,possessing different nature and composition.

435. The earthy matters thus added to the soil canhardly be called manures, although in truth they consi-derably resemble manures in the mode in which they act.By draining, deep ploughing, mixing, and by the use ofmineral manures, either the mechanical texture of thesoil is improved, or substances are added to it in whichit was previously deficient.

436. It is unnecessary to say anything respecting theimportance of draining, and the change which it producesin too retentive soils. The facts which have previouslybeen stated, show, that too much moisture in a soil ishurtful, preventing the free circulation of air throughoutit, and in several ways interfering with the healthygrowth of plants; this is remedied by draining.

437. By draining, and subsoil ploughing, the accessof air is facilitated, and the decomposition of silicates andsimilar stony compounds in the earth is assisted. Inmixing, or by adding mineral manures, we increase thequantity of certain inorganic compounds of the soil.