Changes

Soil. The soil is a superficial covering of the earth's crust, more or less well adapted to the growth of plants. It is usually only a few inches thick. Below this is a subsoil often differing, especially in humid climates, from the soil proper in color, texture, or chemical composition. A very striking definition has been suggested by Sir John B. Lawes, who considered the soil to be rotten subsoil, and the subsoil rotting rock. The term soil is occasionally used in a more comprehensive way to include both the soil and the subsoil.

Soil. The soil is a superficial covering of the earth's crust, more or less well adapted to the growth of plants. It is usually only a few inches thick. Below this is a subsoil often differing, especially in humid climates, from the soil proper in color, texture, or chemical composition. A very striking definition has been suggested by Sir John B. Lawes, who considered the soil to be rotten subsoil, and the subsoil rotting rock. The term soil is occasionally used in a more comprehensive way to include both the soil and the subsoil.

The soil adapted to the growth of the higher plants consists of fragments of rocks or minerals, organic matter, soil solution, and a soil atmosphere. The mineral fragments vary in size from the finest clay particles to gravel and even boulders. The organic matter is derived from low organisms, from previous vegetation, or from growing plants; as also from stable manure, and occasionally fish or animal matter added to the soil by man. The soil solution consists of water carrying dissolved substances derived from the soil grains and from the organic matter, as well as from fertilizing materials artificially applied, and constitutes a nutrient solution from which the plant derives its mineral constituents. The soil atmosphere differs from the ordinary atmosphere above the soil in being richer in carbon dioxide and nitrogen, and containing more water vapor and less oxygen.

The soil adapted to the growth of the higher plants consists of fragments of rocks or [[mineral]]s, organic matter, soil solution, and a soil atmosphere. The mineral fragments vary in size from the finest [[clay]] particles to gravel and even boulders. The organic matter is derived from low organisms, from previous vegetation, or from growing plants; as also from [[stable manure]], and occasionally fish or animal matter added to the soil by man. The soil solution consists of water carrying dissolved substances derived from the soil grains and from the organic matter, as well as from fertilizing materials artificially applied, and constitutes a [[nutrient]] solution from which the plant derives its mineral constituents. The soil atmosphere differs from the ordinary atmosphere above the soil in being richer in [[carbon dioxide]] and [[nitrogen]], and containing more water vapor and less [[oxygen]].

In origin there are two main classes of soils: sedimentary soils, formed by the disintegration and decomposition of rocks in place; and transported soils, including those of alluvial, glacial, and aeolian origin. The word alluvial is here used to include all water-transported material; the term is, however, frequently used in a more specific sense to indicate the recent flood deposit of rivers.

In origin there are two main classes of soils: sedimentary soils, formed by the disintegration and decomposition of rocks in place; and transported soils, including those of alluvial, glacial, and aeolian origin. The word alluvial is here used to include all water-transported material; the term is, however, frequently used in a more specific sense to indicate the recent flood deposit of rivers.