---------------------------------------------------------------------- | | Salts of | Salts of | Silica. | | Potash and | Lime and | | | Soda. | Magnesia. | |----------------------------------|------------|-----------|--------- |Silica { Oat straw with seeds | 34.00 | 4.00 | 62.00 |Plants. { Wheat straw | 22.50 | 7.20 | 61.50 | { Barley straw with seeds| 19.00 | 25.70 | 55.30 | { Rye straw | 18.65 | 16.52 | 63.89 | { Good hay | 6.00 | 34.00 | 60.00 |Lime { Tobacco | 24.34 | 67.44 | 8.30 |Plants { Pea straw | 27.82 | 63.74 | 7.81 | { Potato plant | 4.20 | 59.40 | 36.40 | { Meadow Clover | 39.20 | 56.00 | 4.90 |Potash { Maize straw | 72.45 | 6.50 | 18.00 |Plants. { Turnips | 81.60 | 18.40 | -- | { Beet root | 88.00 | 12.00 | -- | { Potatoes | 85.81 | 14.19 | -- | { Jerusalem Artichoke | 84.30 | 15.70 | -- ---------------------------------------------------------------------- The special application of these facts must be reserved till we come to treat of the rotation of crops. It is manifest that, as the crops removed from the soil all contain a greater or less amount of inorganic matters, they must be continually undergoing diminution, and at length be completely exhausted unless their quantity is maintained from some external source. In many cases the supply of these substances is so large that ages may elapse before this becomes apparent, but where the quantity is small, a system of reckless cropping may reduce a soil to a state of absolute sterility. A remarkable illustration of this fact is found in the virgin soils of America, from which the early settlers reaped almost unheard-of crops, but, by injudicious cultivation, they were soon exhausted and abandoned, new tracts being brought in and cultivated only to be in their turn abandoned. The knowledge of the composition of the ash of plants assists us in ascertaining how this exhaustion may be avoided, and indicates the mode in which such soils may be preserved in a fertile state. FOOTNOTES: [Footnote A: Apparently a species of Sinapis.] [Footnote B: Oxide of Manganese, 0.42.] [Footnote C: Oxide of Manganese, 0.92.] [Footnote D: Alumina, 1.02.] [Footnote E: Alumina, 0.63.] [Footnote F: Iodide of Potassium, 0.44; Sulphuret of Sodium, 3.66.] [Footnote G: Iodide of Potassium, 0.23.] [Footnote H: Iodide of Potassium, 1.68.] CHAPTER V. THE SOIL--ITS CHEMICAL AND PHYSICAL CHARACTERS.