The Garden Guide

Book: Gardening Science - Soils, Manure and the Environment
Chapter: Chapter 1: Earths and Soils

Inorganic plant foods

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1165. The inorganic substances which are found in plants consist chiefly of earthy and alkaline compounds, with a small proportion of iron or manganese: these are left in the form of ashes when the plants are burnt. The ashes of a plant, however, cannot be considered as exactly representing the inorganic substances which it contained; because, in burning, various organic acids are destroyed, with which the alkaline bases were previously combined: hence the ashes of plants are always more or less strongly alkaline. The substances thus left when a plant is burnt are, potash, soda, and lime caustic or carbonated, being derived from the destruction of various compounds with organic acids; salts of the same substances and magnesia, with sulphuric and phosphoric acids, chlorine, &c.,-silica, and the oxides of iron and maganese. In the same way that salts of organic acids are destroyed by burning, so are those of nitric acid, such as nitrate of potash and soda, which are not unfrequently present in plants: the nitric acid is decomposed, but the potash or soda with which it was combined is found in the ashes.