THE SOIL, ITS NATURE AND COMPOSITION 61 



THE SOIL, ITS NATURE AND COMPOSITION 



Soil is the term applied to the upper crust of the earth's surface 

 which has been ground and powdered into a more or less fine state by 

 the action of man and the weather. It consists of particles of various 

 kinds of rock mixed with decayed or decaying animal and vegetable 

 matters. Beneath the soil in which the roots of plants grow is what 

 is termed the subsoil. This may be a bed of clay, sand, limestone, 

 gravel &c., and is generally not in a condition to supply the roots of 

 plants with the food they require until it has been tilled and mixed with 

 the surface soil. 



Soil absorbs and radiates heat and moisture and is gradually being 

 broken up into smaller fragments by the action of heat, cold, moisture, 

 and the gases of the air. Frost plays an important part in breaking 

 down particles of rock and converting them into soil. The frozen water 

 (ice) pushes the particles asunder and with the increase of temperature 

 they fall apart. The absorption of heat by day and its radiation by 

 night also reduce the soil to a finer condition. And the roots of plants 

 themselves have the power of breaking up particles of rock, and even 

 of dissolving by their action mineral substances not readily soluble in 

 water. In fact a change is always going on in the soil, and the 

 gardener simply hastens the process by his operations. It is as well, 

 however, that he should always bear in mind that it is the upper layer 

 of the earth's surface, and not that two, three, or more feet below it, that 

 is likely to contain available food for the plants he grows. And although 

 the under la.yers constituting the sub-soil may be broken up when 

 occasion requires or opportunity permits, they should never be brought 

 to the surface as a medium for the roots of plants to grow in. 



Kinds of Soil. — Soils for gardening purposes are usually spoken of as 

 sandy, clayey, loamy, peaty, chalky, and gravelly. A mixture of these 

 is on the whole better than any one of them by itself ; although for 

 certain plants it may be better if one or other sometimes predominates. 



Sandy and Gravelly Soils are of little value by themselves, but may 

 be improved by the addition of clay, vegetable matter or humus and lime 

 or chalk. By this means a loose gravelly soil is rendered more 

 adhesive, and the roots are enabled to perform their functions without 

 being torn about by the wind. 



Clayey Soils are too sticky and retentive of water to be of any use 

 to plants. They require to be broken up and mixed with sand, ashes, 

 lime, humus, &c., until they are rendered sufficiently porous and at the 

 same time capable of retaining moisture in the particles. 



